3111 lines
86 KiB
C
3111 lines
86 KiB
C
/*
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* Memory merging support.
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*
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* This code enables dynamic sharing of identical pages found in different
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* memory areas, even if they are not shared by fork()
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*
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* Copyright (C) 2008-2009 Red Hat, Inc.
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* Authors:
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* Izik Eidus
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* Andrea Arcangeli
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* Chris Wright
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* Hugh Dickins
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*
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* This work is licensed under the terms of the GNU GPL, version 2.
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*/
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#include <linux/errno.h>
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#include <linux/mm.h>
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#include <linux/fs.h>
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#include <linux/mman.h>
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#include <linux/sched.h>
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#include <linux/sched/mm.h>
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#include <linux/sched/coredump.h>
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#include <linux/rwsem.h>
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#include <linux/pagemap.h>
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#include <linux/rmap.h>
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#include <linux/spinlock.h>
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#include <linux/jhash.h>
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#include <linux/delay.h>
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#include <linux/kthread.h>
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#include <linux/wait.h>
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#include <linux/slab.h>
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#include <linux/rbtree.h>
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#include <linux/memory.h>
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#include <linux/mmu_notifier.h>
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#include <linux/swap.h>
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#include <linux/ksm.h>
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#include <linux/hashtable.h>
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#include <linux/freezer.h>
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#include <linux/oom.h>
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#include <linux/numa.h>
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#include <asm/tlbflush.h>
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#include "internal.h"
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#ifdef CONFIG_NUMA
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#define NUMA(x) (x)
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#define DO_NUMA(x) do { (x); } while (0)
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#else
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#define NUMA(x) (0)
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#define DO_NUMA(x) do { } while (0)
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#endif
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/*
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* A few notes about the KSM scanning process,
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* to make it easier to understand the data structures below:
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*
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* In order to reduce excessive scanning, KSM sorts the memory pages by their
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* contents into a data structure that holds pointers to the pages' locations.
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*
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* Since the contents of the pages may change at any moment, KSM cannot just
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* insert the pages into a normal sorted tree and expect it to find anything.
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* Therefore KSM uses two data structures - the stable and the unstable tree.
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*
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* The stable tree holds pointers to all the merged pages (ksm pages), sorted
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* by their contents. Because each such page is write-protected, searching on
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* this tree is fully assured to be working (except when pages are unmapped),
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* and therefore this tree is called the stable tree.
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*
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* In addition to the stable tree, KSM uses a second data structure called the
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* unstable tree: this tree holds pointers to pages which have been found to
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* be "unchanged for a period of time". The unstable tree sorts these pages
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* by their contents, but since they are not write-protected, KSM cannot rely
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* upon the unstable tree to work correctly - the unstable tree is liable to
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* be corrupted as its contents are modified, and so it is called unstable.
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*
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* KSM solves this problem by several techniques:
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*
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* 1) The unstable tree is flushed every time KSM completes scanning all
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* memory areas, and then the tree is rebuilt again from the beginning.
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* 2) KSM will only insert into the unstable tree, pages whose hash value
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* has not changed since the previous scan of all memory areas.
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* 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
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* colors of the nodes and not on their contents, assuring that even when
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* the tree gets "corrupted" it won't get out of balance, so scanning time
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* remains the same (also, searching and inserting nodes in an rbtree uses
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* the same algorithm, so we have no overhead when we flush and rebuild).
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* 4) KSM never flushes the stable tree, which means that even if it were to
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* take 10 attempts to find a page in the unstable tree, once it is found,
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* it is secured in the stable tree. (When we scan a new page, we first
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* compare it against the stable tree, and then against the unstable tree.)
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*
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* If the merge_across_nodes tunable is unset, then KSM maintains multiple
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* stable trees and multiple unstable trees: one of each for each NUMA node.
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*/
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/**
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* struct mm_slot - ksm information per mm that is being scanned
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* @link: link to the mm_slots hash list
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* @mm_list: link into the mm_slots list, rooted in ksm_mm_head
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* @rmap_list: head for this mm_slot's singly-linked list of rmap_items
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* @mm: the mm that this information is valid for
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*/
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struct mm_slot {
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struct hlist_node link;
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struct list_head mm_list;
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struct rmap_item *rmap_list;
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struct mm_struct *mm;
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};
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/**
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* struct ksm_scan - cursor for scanning
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* @mm_slot: the current mm_slot we are scanning
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* @address: the next address inside that to be scanned
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* @rmap_list: link to the next rmap to be scanned in the rmap_list
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* @seqnr: count of completed full scans (needed when removing unstable node)
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*
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* There is only the one ksm_scan instance of this cursor structure.
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*/
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struct ksm_scan {
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struct mm_slot *mm_slot;
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unsigned long address;
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struct rmap_item **rmap_list;
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unsigned long seqnr;
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};
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/**
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* struct stable_node - node of the stable rbtree
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* @node: rb node of this ksm page in the stable tree
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* @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
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* @hlist_dup: linked into the stable_node->hlist with a stable_node chain
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* @list: linked into migrate_nodes, pending placement in the proper node tree
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* @hlist: hlist head of rmap_items using this ksm page
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* @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
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* @chain_prune_time: time of the last full garbage collection
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* @rmap_hlist_len: number of rmap_item entries in hlist or STABLE_NODE_CHAIN
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* @nid: NUMA node id of stable tree in which linked (may not match kpfn)
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*/
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struct stable_node {
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union {
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struct rb_node node; /* when node of stable tree */
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struct { /* when listed for migration */
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struct list_head *head;
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struct {
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struct hlist_node hlist_dup;
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struct list_head list;
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};
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};
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};
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struct hlist_head hlist;
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union {
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unsigned long kpfn;
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unsigned long chain_prune_time;
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};
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/*
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* STABLE_NODE_CHAIN can be any negative number in
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* rmap_hlist_len negative range, but better not -1 to be able
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* to reliably detect underflows.
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*/
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#define STABLE_NODE_CHAIN -1024
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int rmap_hlist_len;
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#ifdef CONFIG_NUMA
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int nid;
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#endif
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};
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/**
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* struct rmap_item - reverse mapping item for virtual addresses
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* @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
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* @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
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* @nid: NUMA node id of unstable tree in which linked (may not match page)
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* @mm: the memory structure this rmap_item is pointing into
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* @address: the virtual address this rmap_item tracks (+ flags in low bits)
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* @oldchecksum: previous checksum of the page at that virtual address
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* @node: rb node of this rmap_item in the unstable tree
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* @head: pointer to stable_node heading this list in the stable tree
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* @hlist: link into hlist of rmap_items hanging off that stable_node
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*/
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struct rmap_item {
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struct rmap_item *rmap_list;
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union {
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struct anon_vma *anon_vma; /* when stable */
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#ifdef CONFIG_NUMA
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int nid; /* when node of unstable tree */
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#endif
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};
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struct mm_struct *mm;
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unsigned long address; /* + low bits used for flags below */
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unsigned int oldchecksum; /* when unstable */
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union {
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struct rb_node node; /* when node of unstable tree */
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struct { /* when listed from stable tree */
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struct stable_node *head;
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struct hlist_node hlist;
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};
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};
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};
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#define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
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#define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
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#define STABLE_FLAG 0x200 /* is listed from the stable tree */
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/* The stable and unstable tree heads */
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static struct rb_root one_stable_tree[1] = { RB_ROOT };
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static struct rb_root one_unstable_tree[1] = { RB_ROOT };
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static struct rb_root *root_stable_tree = one_stable_tree;
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static struct rb_root *root_unstable_tree = one_unstable_tree;
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/* Recently migrated nodes of stable tree, pending proper placement */
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static LIST_HEAD(migrate_nodes);
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#define STABLE_NODE_DUP_HEAD ((struct list_head *)&migrate_nodes.prev)
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#define MM_SLOTS_HASH_BITS 10
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static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
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static struct mm_slot ksm_mm_head = {
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.mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
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};
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static struct ksm_scan ksm_scan = {
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.mm_slot = &ksm_mm_head,
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};
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static struct kmem_cache *rmap_item_cache;
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static struct kmem_cache *stable_node_cache;
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static struct kmem_cache *mm_slot_cache;
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/* The number of nodes in the stable tree */
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static unsigned long ksm_pages_shared;
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/* The number of page slots additionally sharing those nodes */
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static unsigned long ksm_pages_sharing;
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/* The number of nodes in the unstable tree */
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static unsigned long ksm_pages_unshared;
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/* The number of rmap_items in use: to calculate pages_volatile */
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static unsigned long ksm_rmap_items;
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/* The number of stable_node chains */
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static unsigned long ksm_stable_node_chains;
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/* The number of stable_node dups linked to the stable_node chains */
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static unsigned long ksm_stable_node_dups;
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/* Delay in pruning stale stable_node_dups in the stable_node_chains */
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static int ksm_stable_node_chains_prune_millisecs = 2000;
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/* Maximum number of page slots sharing a stable node */
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static int ksm_max_page_sharing = 256;
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/* Number of pages ksmd should scan in one batch */
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static unsigned int ksm_thread_pages_to_scan = 100;
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/* Milliseconds ksmd should sleep between batches */
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static unsigned int ksm_thread_sleep_millisecs = 20;
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/* Checksum of an empty (zeroed) page */
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static unsigned int zero_checksum __read_mostly;
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/* Whether to merge empty (zeroed) pages with actual zero pages */
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static bool ksm_use_zero_pages __read_mostly;
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#ifdef CONFIG_NUMA
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/* Zeroed when merging across nodes is not allowed */
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static unsigned int ksm_merge_across_nodes = 1;
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static int ksm_nr_node_ids = 1;
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#else
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#define ksm_merge_across_nodes 1U
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#define ksm_nr_node_ids 1
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#endif
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#define KSM_RUN_STOP 0
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#define KSM_RUN_MERGE 1
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#define KSM_RUN_UNMERGE 2
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#define KSM_RUN_OFFLINE 4
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static unsigned long ksm_run = KSM_RUN_STOP;
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static void wait_while_offlining(void);
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static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
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static DEFINE_MUTEX(ksm_thread_mutex);
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static DEFINE_SPINLOCK(ksm_mmlist_lock);
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#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
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sizeof(struct __struct), __alignof__(struct __struct),\
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(__flags), NULL)
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static int __init ksm_slab_init(void)
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{
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rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
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if (!rmap_item_cache)
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goto out;
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stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
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if (!stable_node_cache)
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goto out_free1;
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mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
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if (!mm_slot_cache)
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goto out_free2;
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return 0;
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out_free2:
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kmem_cache_destroy(stable_node_cache);
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out_free1:
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kmem_cache_destroy(rmap_item_cache);
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out:
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return -ENOMEM;
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}
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static void __init ksm_slab_free(void)
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{
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kmem_cache_destroy(mm_slot_cache);
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kmem_cache_destroy(stable_node_cache);
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kmem_cache_destroy(rmap_item_cache);
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mm_slot_cache = NULL;
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}
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static __always_inline bool is_stable_node_chain(struct stable_node *chain)
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{
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return chain->rmap_hlist_len == STABLE_NODE_CHAIN;
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}
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static __always_inline bool is_stable_node_dup(struct stable_node *dup)
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{
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return dup->head == STABLE_NODE_DUP_HEAD;
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}
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static inline void stable_node_chain_add_dup(struct stable_node *dup,
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struct stable_node *chain)
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{
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VM_BUG_ON(is_stable_node_dup(dup));
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dup->head = STABLE_NODE_DUP_HEAD;
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VM_BUG_ON(!is_stable_node_chain(chain));
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hlist_add_head(&dup->hlist_dup, &chain->hlist);
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ksm_stable_node_dups++;
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}
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static inline void __stable_node_dup_del(struct stable_node *dup)
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{
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VM_BUG_ON(!is_stable_node_dup(dup));
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hlist_del(&dup->hlist_dup);
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ksm_stable_node_dups--;
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}
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static inline void stable_node_dup_del(struct stable_node *dup)
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{
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VM_BUG_ON(is_stable_node_chain(dup));
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if (is_stable_node_dup(dup))
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__stable_node_dup_del(dup);
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else
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rb_erase(&dup->node, root_stable_tree + NUMA(dup->nid));
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#ifdef CONFIG_DEBUG_VM
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dup->head = NULL;
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#endif
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}
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static inline struct rmap_item *alloc_rmap_item(void)
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{
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struct rmap_item *rmap_item;
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rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL |
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__GFP_NORETRY | __GFP_NOWARN);
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if (rmap_item)
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ksm_rmap_items++;
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return rmap_item;
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}
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static inline void free_rmap_item(struct rmap_item *rmap_item)
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{
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ksm_rmap_items--;
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rmap_item->mm = NULL; /* debug safety */
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kmem_cache_free(rmap_item_cache, rmap_item);
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}
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static inline struct stable_node *alloc_stable_node(void)
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{
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/*
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* The allocation can take too long with GFP_KERNEL when memory is under
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* pressure, which may lead to hung task warnings. Adding __GFP_HIGH
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* grants access to memory reserves, helping to avoid this problem.
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*/
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return kmem_cache_alloc(stable_node_cache, GFP_KERNEL | __GFP_HIGH);
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}
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static inline void free_stable_node(struct stable_node *stable_node)
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{
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VM_BUG_ON(stable_node->rmap_hlist_len &&
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!is_stable_node_chain(stable_node));
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kmem_cache_free(stable_node_cache, stable_node);
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}
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static inline struct mm_slot *alloc_mm_slot(void)
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{
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if (!mm_slot_cache) /* initialization failed */
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return NULL;
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return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
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}
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static inline void free_mm_slot(struct mm_slot *mm_slot)
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{
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kmem_cache_free(mm_slot_cache, mm_slot);
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}
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static struct mm_slot *get_mm_slot(struct mm_struct *mm)
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{
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struct mm_slot *slot;
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hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm)
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if (slot->mm == mm)
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return slot;
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return NULL;
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}
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static void insert_to_mm_slots_hash(struct mm_struct *mm,
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struct mm_slot *mm_slot)
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{
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mm_slot->mm = mm;
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hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm);
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}
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/*
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* ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
|
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* page tables after it has passed through ksm_exit() - which, if necessary,
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* takes mmap_sem briefly to serialize against them. ksm_exit() does not set
|
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* a special flag: they can just back out as soon as mm_users goes to zero.
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* ksm_test_exit() is used throughout to make this test for exit: in some
|
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* places for correctness, in some places just to avoid unnecessary work.
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*/
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static inline bool ksm_test_exit(struct mm_struct *mm)
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{
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return atomic_read(&mm->mm_users) == 0;
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}
|
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|
|
/*
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|
* We use break_ksm to break COW on a ksm page: it's a stripped down
|
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*
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* if (get_user_pages(addr, 1, 1, 1, &page, NULL) == 1)
|
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* put_page(page);
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*
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* but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
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* in case the application has unmapped and remapped mm,addr meanwhile.
|
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* Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
|
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* mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
|
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*
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* FAULT_FLAG/FOLL_REMOTE are because we do this outside the context
|
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* of the process that owns 'vma'. We also do not want to enforce
|
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* protection keys here anyway.
|
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*/
|
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static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
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|
{
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struct page *page;
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int ret = 0;
|
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|
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do {
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cond_resched();
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page = follow_page(vma, addr,
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FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE);
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if (IS_ERR_OR_NULL(page))
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break;
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if (PageKsm(page))
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ret = handle_mm_fault(vma, addr,
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FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE);
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else
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ret = VM_FAULT_WRITE;
|
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put_page(page);
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} while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM)));
|
|
/*
|
|
* We must loop because handle_mm_fault() may back out if there's
|
|
* any difficulty e.g. if pte accessed bit gets updated concurrently.
|
|
*
|
|
* VM_FAULT_WRITE is what we have been hoping for: it indicates that
|
|
* COW has been broken, even if the vma does not permit VM_WRITE;
|
|
* but note that a concurrent fault might break PageKsm for us.
|
|
*
|
|
* VM_FAULT_SIGBUS could occur if we race with truncation of the
|
|
* backing file, which also invalidates anonymous pages: that's
|
|
* okay, that truncation will have unmapped the PageKsm for us.
|
|
*
|
|
* VM_FAULT_OOM: at the time of writing (late July 2009), setting
|
|
* aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
|
|
* current task has TIF_MEMDIE set, and will be OOM killed on return
|
|
* to user; and ksmd, having no mm, would never be chosen for that.
|
|
*
|
|
* But if the mm is in a limited mem_cgroup, then the fault may fail
|
|
* with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
|
|
* even ksmd can fail in this way - though it's usually breaking ksm
|
|
* just to undo a merge it made a moment before, so unlikely to oom.
|
|
*
|
|
* That's a pity: we might therefore have more kernel pages allocated
|
|
* than we're counting as nodes in the stable tree; but ksm_do_scan
|
|
* will retry to break_cow on each pass, so should recover the page
|
|
* in due course. The important thing is to not let VM_MERGEABLE
|
|
* be cleared while any such pages might remain in the area.
|
|
*/
|
|
return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
|
|
}
|
|
|
|
static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
|
|
unsigned long addr)
|
|
{
|
|
struct vm_area_struct *vma;
|
|
if (ksm_test_exit(mm))
|
|
return NULL;
|
|
vma = find_vma(mm, addr);
|
|
if (!vma || vma->vm_start > addr)
|
|
return NULL;
|
|
if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
|
|
return NULL;
|
|
return vma;
|
|
}
|
|
|
|
static void break_cow(struct rmap_item *rmap_item)
|
|
{
|
|
struct mm_struct *mm = rmap_item->mm;
|
|
unsigned long addr = rmap_item->address;
|
|
struct vm_area_struct *vma;
|
|
|
|
/*
|
|
* It is not an accident that whenever we want to break COW
|
|
* to undo, we also need to drop a reference to the anon_vma.
|
|
*/
|
|
put_anon_vma(rmap_item->anon_vma);
|
|
|
|
down_read(&mm->mmap_sem);
|
|
vma = find_mergeable_vma(mm, addr);
|
|
if (vma)
|
|
break_ksm(vma, addr);
|
|
up_read(&mm->mmap_sem);
|
|
}
|
|
|
|
static struct page *get_mergeable_page(struct rmap_item *rmap_item)
|
|
{
|
|
struct mm_struct *mm = rmap_item->mm;
|
|
unsigned long addr = rmap_item->address;
|
|
struct vm_area_struct *vma;
|
|
struct page *page;
|
|
|
|
down_read(&mm->mmap_sem);
|
|
vma = find_mergeable_vma(mm, addr);
|
|
if (!vma)
|
|
goto out;
|
|
|
|
page = follow_page(vma, addr, FOLL_GET);
|
|
if (IS_ERR_OR_NULL(page))
|
|
goto out;
|
|
if (PageAnon(page)) {
|
|
flush_anon_page(vma, page, addr);
|
|
flush_dcache_page(page);
|
|
} else {
|
|
put_page(page);
|
|
out:
|
|
page = NULL;
|
|
}
|
|
up_read(&mm->mmap_sem);
|
|
return page;
|
|
}
|
|
|
|
/*
|
|
* This helper is used for getting right index into array of tree roots.
|
|
* When merge_across_nodes knob is set to 1, there are only two rb-trees for
|
|
* stable and unstable pages from all nodes with roots in index 0. Otherwise,
|
|
* every node has its own stable and unstable tree.
|
|
*/
|
|
static inline int get_kpfn_nid(unsigned long kpfn)
|
|
{
|
|
return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn));
|
|
}
|
|
|
|
static struct stable_node *alloc_stable_node_chain(struct stable_node *dup,
|
|
struct rb_root *root)
|
|
{
|
|
struct stable_node *chain = alloc_stable_node();
|
|
VM_BUG_ON(is_stable_node_chain(dup));
|
|
if (likely(chain)) {
|
|
INIT_HLIST_HEAD(&chain->hlist);
|
|
chain->chain_prune_time = jiffies;
|
|
chain->rmap_hlist_len = STABLE_NODE_CHAIN;
|
|
#if defined (CONFIG_DEBUG_VM) && defined(CONFIG_NUMA)
|
|
chain->nid = -1; /* debug */
|
|
#endif
|
|
ksm_stable_node_chains++;
|
|
|
|
/*
|
|
* Put the stable node chain in the first dimension of
|
|
* the stable tree and at the same time remove the old
|
|
* stable node.
|
|
*/
|
|
rb_replace_node(&dup->node, &chain->node, root);
|
|
|
|
/*
|
|
* Move the old stable node to the second dimension
|
|
* queued in the hlist_dup. The invariant is that all
|
|
* dup stable_nodes in the chain->hlist point to pages
|
|
* that are wrprotected and have the exact same
|
|
* content.
|
|
*/
|
|
stable_node_chain_add_dup(dup, chain);
|
|
}
|
|
return chain;
|
|
}
|
|
|
|
static inline void free_stable_node_chain(struct stable_node *chain,
|
|
struct rb_root *root)
|
|
{
|
|
rb_erase(&chain->node, root);
|
|
free_stable_node(chain);
|
|
ksm_stable_node_chains--;
|
|
}
|
|
|
|
static void remove_node_from_stable_tree(struct stable_node *stable_node)
|
|
{
|
|
struct rmap_item *rmap_item;
|
|
|
|
/* check it's not STABLE_NODE_CHAIN or negative */
|
|
BUG_ON(stable_node->rmap_hlist_len < 0);
|
|
|
|
hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
|
|
if (rmap_item->hlist.next)
|
|
ksm_pages_sharing--;
|
|
else
|
|
ksm_pages_shared--;
|
|
VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
|
|
stable_node->rmap_hlist_len--;
|
|
put_anon_vma(rmap_item->anon_vma);
|
|
rmap_item->address &= PAGE_MASK;
|
|
cond_resched();
|
|
}
|
|
|
|
/*
|
|
* We need the second aligned pointer of the migrate_nodes
|
|
* list_head to stay clear from the rb_parent_color union
|
|
* (aligned and different than any node) and also different
|
|
* from &migrate_nodes. This will verify that future list.h changes
|
|
* don't break STABLE_NODE_DUP_HEAD.
|
|
*/
|
|
#if GCC_VERSION >= 40903 /* only recent gcc can handle it */
|
|
BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes);
|
|
BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1);
|
|
#endif
|
|
|
|
if (stable_node->head == &migrate_nodes)
|
|
list_del(&stable_node->list);
|
|
else
|
|
stable_node_dup_del(stable_node);
|
|
free_stable_node(stable_node);
|
|
}
|
|
|
|
/*
|
|
* get_ksm_page: checks if the page indicated by the stable node
|
|
* is still its ksm page, despite having held no reference to it.
|
|
* In which case we can trust the content of the page, and it
|
|
* returns the gotten page; but if the page has now been zapped,
|
|
* remove the stale node from the stable tree and return NULL.
|
|
* But beware, the stable node's page might be being migrated.
|
|
*
|
|
* You would expect the stable_node to hold a reference to the ksm page.
|
|
* But if it increments the page's count, swapping out has to wait for
|
|
* ksmd to come around again before it can free the page, which may take
|
|
* seconds or even minutes: much too unresponsive. So instead we use a
|
|
* "keyhole reference": access to the ksm page from the stable node peeps
|
|
* out through its keyhole to see if that page still holds the right key,
|
|
* pointing back to this stable node. This relies on freeing a PageAnon
|
|
* page to reset its page->mapping to NULL, and relies on no other use of
|
|
* a page to put something that might look like our key in page->mapping.
|
|
* is on its way to being freed; but it is an anomaly to bear in mind.
|
|
*/
|
|
static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it)
|
|
{
|
|
struct page *page;
|
|
void *expected_mapping;
|
|
unsigned long kpfn;
|
|
|
|
expected_mapping = (void *)((unsigned long)stable_node |
|
|
PAGE_MAPPING_KSM);
|
|
again:
|
|
kpfn = READ_ONCE(stable_node->kpfn);
|
|
page = pfn_to_page(kpfn);
|
|
|
|
/*
|
|
* page is computed from kpfn, so on most architectures reading
|
|
* page->mapping is naturally ordered after reading node->kpfn,
|
|
* but on Alpha we need to be more careful.
|
|
*/
|
|
smp_read_barrier_depends();
|
|
if (READ_ONCE(page->mapping) != expected_mapping)
|
|
goto stale;
|
|
|
|
/*
|
|
* We cannot do anything with the page while its refcount is 0.
|
|
* Usually 0 means free, or tail of a higher-order page: in which
|
|
* case this node is no longer referenced, and should be freed;
|
|
* however, it might mean that the page is under page_freeze_refs().
|
|
* The __remove_mapping() case is easy, again the node is now stale;
|
|
* but if page is swapcache in migrate_page_move_mapping(), it might
|
|
* still be our page, in which case it's essential to keep the node.
|
|
*/
|
|
while (!get_page_unless_zero(page)) {
|
|
/*
|
|
* Another check for page->mapping != expected_mapping would
|
|
* work here too. We have chosen the !PageSwapCache test to
|
|
* optimize the common case, when the page is or is about to
|
|
* be freed: PageSwapCache is cleared (under spin_lock_irq)
|
|
* in the freeze_refs section of __remove_mapping(); but Anon
|
|
* page->mapping reset to NULL later, in free_pages_prepare().
|
|
*/
|
|
if (!PageSwapCache(page))
|
|
goto stale;
|
|
cpu_relax();
|
|
}
|
|
|
|
if (READ_ONCE(page->mapping) != expected_mapping) {
|
|
put_page(page);
|
|
goto stale;
|
|
}
|
|
|
|
if (lock_it) {
|
|
lock_page(page);
|
|
if (READ_ONCE(page->mapping) != expected_mapping) {
|
|
unlock_page(page);
|
|
put_page(page);
|
|
goto stale;
|
|
}
|
|
}
|
|
return page;
|
|
|
|
stale:
|
|
/*
|
|
* We come here from above when page->mapping or !PageSwapCache
|
|
* suggests that the node is stale; but it might be under migration.
|
|
* We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(),
|
|
* before checking whether node->kpfn has been changed.
|
|
*/
|
|
smp_rmb();
|
|
if (READ_ONCE(stable_node->kpfn) != kpfn)
|
|
goto again;
|
|
remove_node_from_stable_tree(stable_node);
|
|
return NULL;
|
|
}
|
|
|
|
/*
|
|
* Removing rmap_item from stable or unstable tree.
|
|
* This function will clean the information from the stable/unstable tree.
|
|
*/
|
|
static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
|
|
{
|
|
if (rmap_item->address & STABLE_FLAG) {
|
|
struct stable_node *stable_node;
|
|
struct page *page;
|
|
|
|
stable_node = rmap_item->head;
|
|
page = get_ksm_page(stable_node, true);
|
|
if (!page)
|
|
goto out;
|
|
|
|
hlist_del(&rmap_item->hlist);
|
|
unlock_page(page);
|
|
put_page(page);
|
|
|
|
if (!hlist_empty(&stable_node->hlist))
|
|
ksm_pages_sharing--;
|
|
else
|
|
ksm_pages_shared--;
|
|
VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
|
|
stable_node->rmap_hlist_len--;
|
|
|
|
put_anon_vma(rmap_item->anon_vma);
|
|
rmap_item->address &= PAGE_MASK;
|
|
|
|
} else if (rmap_item->address & UNSTABLE_FLAG) {
|
|
unsigned char age;
|
|
/*
|
|
* Usually ksmd can and must skip the rb_erase, because
|
|
* root_unstable_tree was already reset to RB_ROOT.
|
|
* But be careful when an mm is exiting: do the rb_erase
|
|
* if this rmap_item was inserted by this scan, rather
|
|
* than left over from before.
|
|
*/
|
|
age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
|
|
BUG_ON(age > 1);
|
|
if (!age)
|
|
rb_erase(&rmap_item->node,
|
|
root_unstable_tree + NUMA(rmap_item->nid));
|
|
ksm_pages_unshared--;
|
|
rmap_item->address &= PAGE_MASK;
|
|
}
|
|
out:
|
|
cond_resched(); /* we're called from many long loops */
|
|
}
|
|
|
|
static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
|
|
struct rmap_item **rmap_list)
|
|
{
|
|
while (*rmap_list) {
|
|
struct rmap_item *rmap_item = *rmap_list;
|
|
*rmap_list = rmap_item->rmap_list;
|
|
remove_rmap_item_from_tree(rmap_item);
|
|
free_rmap_item(rmap_item);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Though it's very tempting to unmerge rmap_items from stable tree rather
|
|
* than check every pte of a given vma, the locking doesn't quite work for
|
|
* that - an rmap_item is assigned to the stable tree after inserting ksm
|
|
* page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
|
|
* rmap_items from parent to child at fork time (so as not to waste time
|
|
* if exit comes before the next scan reaches it).
|
|
*
|
|
* Similarly, although we'd like to remove rmap_items (so updating counts
|
|
* and freeing memory) when unmerging an area, it's easier to leave that
|
|
* to the next pass of ksmd - consider, for example, how ksmd might be
|
|
* in cmp_and_merge_page on one of the rmap_items we would be removing.
|
|
*/
|
|
static int unmerge_ksm_pages(struct vm_area_struct *vma,
|
|
unsigned long start, unsigned long end)
|
|
{
|
|
unsigned long addr;
|
|
int err = 0;
|
|
|
|
for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
|
|
if (ksm_test_exit(vma->vm_mm))
|
|
break;
|
|
if (signal_pending(current))
|
|
err = -ERESTARTSYS;
|
|
else
|
|
err = break_ksm(vma, addr);
|
|
}
|
|
return err;
|
|
}
|
|
|
|
#ifdef CONFIG_SYSFS
|
|
/*
|
|
* Only called through the sysfs control interface:
|
|
*/
|
|
static int remove_stable_node(struct stable_node *stable_node)
|
|
{
|
|
struct page *page;
|
|
int err;
|
|
|
|
page = get_ksm_page(stable_node, true);
|
|
if (!page) {
|
|
/*
|
|
* get_ksm_page did remove_node_from_stable_tree itself.
|
|
*/
|
|
return 0;
|
|
}
|
|
|
|
if (WARN_ON_ONCE(page_mapped(page))) {
|
|
/*
|
|
* This should not happen: but if it does, just refuse to let
|
|
* merge_across_nodes be switched - there is no need to panic.
|
|
*/
|
|
err = -EBUSY;
|
|
} else {
|
|
/*
|
|
* The stable node did not yet appear stale to get_ksm_page(),
|
|
* since that allows for an unmapped ksm page to be recognized
|
|
* right up until it is freed; but the node is safe to remove.
|
|
* This page might be in a pagevec waiting to be freed,
|
|
* or it might be PageSwapCache (perhaps under writeback),
|
|
* or it might have been removed from swapcache a moment ago.
|
|
*/
|
|
set_page_stable_node(page, NULL);
|
|
remove_node_from_stable_tree(stable_node);
|
|
err = 0;
|
|
}
|
|
|
|
unlock_page(page);
|
|
put_page(page);
|
|
return err;
|
|
}
|
|
|
|
static int remove_stable_node_chain(struct stable_node *stable_node,
|
|
struct rb_root *root)
|
|
{
|
|
struct stable_node *dup;
|
|
struct hlist_node *hlist_safe;
|
|
|
|
if (!is_stable_node_chain(stable_node)) {
|
|
VM_BUG_ON(is_stable_node_dup(stable_node));
|
|
if (remove_stable_node(stable_node))
|
|
return true;
|
|
else
|
|
return false;
|
|
}
|
|
|
|
hlist_for_each_entry_safe(dup, hlist_safe,
|
|
&stable_node->hlist, hlist_dup) {
|
|
VM_BUG_ON(!is_stable_node_dup(dup));
|
|
if (remove_stable_node(dup))
|
|
return true;
|
|
}
|
|
BUG_ON(!hlist_empty(&stable_node->hlist));
|
|
free_stable_node_chain(stable_node, root);
|
|
return false;
|
|
}
|
|
|
|
static int remove_all_stable_nodes(void)
|
|
{
|
|
struct stable_node *stable_node, *next;
|
|
int nid;
|
|
int err = 0;
|
|
|
|
for (nid = 0; nid < ksm_nr_node_ids; nid++) {
|
|
while (root_stable_tree[nid].rb_node) {
|
|
stable_node = rb_entry(root_stable_tree[nid].rb_node,
|
|
struct stable_node, node);
|
|
if (remove_stable_node_chain(stable_node,
|
|
root_stable_tree + nid)) {
|
|
err = -EBUSY;
|
|
break; /* proceed to next nid */
|
|
}
|
|
cond_resched();
|
|
}
|
|
}
|
|
list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
|
|
if (remove_stable_node(stable_node))
|
|
err = -EBUSY;
|
|
cond_resched();
|
|
}
|
|
return err;
|
|
}
|
|
|
|
static int unmerge_and_remove_all_rmap_items(void)
|
|
{
|
|
struct mm_slot *mm_slot;
|
|
struct mm_struct *mm;
|
|
struct vm_area_struct *vma;
|
|
int err = 0;
|
|
|
|
spin_lock(&ksm_mmlist_lock);
|
|
ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
|
|
struct mm_slot, mm_list);
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
|
|
for (mm_slot = ksm_scan.mm_slot;
|
|
mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
|
|
mm = mm_slot->mm;
|
|
down_read(&mm->mmap_sem);
|
|
for (vma = mm->mmap; vma; vma = vma->vm_next) {
|
|
if (ksm_test_exit(mm))
|
|
break;
|
|
if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
|
|
continue;
|
|
err = unmerge_ksm_pages(vma,
|
|
vma->vm_start, vma->vm_end);
|
|
if (err)
|
|
goto error;
|
|
}
|
|
|
|
remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
|
|
up_read(&mm->mmap_sem);
|
|
|
|
spin_lock(&ksm_mmlist_lock);
|
|
ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
|
|
struct mm_slot, mm_list);
|
|
if (ksm_test_exit(mm)) {
|
|
hash_del(&mm_slot->link);
|
|
list_del(&mm_slot->mm_list);
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
|
|
free_mm_slot(mm_slot);
|
|
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
|
|
mmdrop(mm);
|
|
} else
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
}
|
|
|
|
/* Clean up stable nodes, but don't worry if some are still busy */
|
|
remove_all_stable_nodes();
|
|
ksm_scan.seqnr = 0;
|
|
return 0;
|
|
|
|
error:
|
|
up_read(&mm->mmap_sem);
|
|
spin_lock(&ksm_mmlist_lock);
|
|
ksm_scan.mm_slot = &ksm_mm_head;
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
return err;
|
|
}
|
|
#endif /* CONFIG_SYSFS */
|
|
|
|
static u32 calc_checksum(struct page *page)
|
|
{
|
|
u32 checksum;
|
|
void *addr = kmap_atomic(page);
|
|
checksum = jhash2(addr, PAGE_SIZE / 4, 17);
|
|
kunmap_atomic(addr);
|
|
return checksum;
|
|
}
|
|
|
|
static int memcmp_pages(struct page *page1, struct page *page2)
|
|
{
|
|
char *addr1, *addr2;
|
|
int ret;
|
|
|
|
addr1 = kmap_atomic(page1);
|
|
addr2 = kmap_atomic(page2);
|
|
ret = memcmp(addr1, addr2, PAGE_SIZE);
|
|
kunmap_atomic(addr2);
|
|
kunmap_atomic(addr1);
|
|
return ret;
|
|
}
|
|
|
|
static inline int pages_identical(struct page *page1, struct page *page2)
|
|
{
|
|
return !memcmp_pages(page1, page2);
|
|
}
|
|
|
|
static int write_protect_page(struct vm_area_struct *vma, struct page *page,
|
|
pte_t *orig_pte)
|
|
{
|
|
struct mm_struct *mm = vma->vm_mm;
|
|
struct page_vma_mapped_walk pvmw = {
|
|
.page = page,
|
|
.vma = vma,
|
|
};
|
|
int swapped;
|
|
int err = -EFAULT;
|
|
unsigned long mmun_start; /* For mmu_notifiers */
|
|
unsigned long mmun_end; /* For mmu_notifiers */
|
|
|
|
pvmw.address = page_address_in_vma(page, vma);
|
|
if (pvmw.address == -EFAULT)
|
|
goto out;
|
|
|
|
BUG_ON(PageTransCompound(page));
|
|
|
|
mmun_start = pvmw.address;
|
|
mmun_end = pvmw.address + PAGE_SIZE;
|
|
mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
|
|
|
|
if (!page_vma_mapped_walk(&pvmw))
|
|
goto out_mn;
|
|
if (WARN_ONCE(!pvmw.pte, "Unexpected PMD mapping?"))
|
|
goto out_unlock;
|
|
|
|
if (pte_write(*pvmw.pte) || pte_dirty(*pvmw.pte) ||
|
|
(pte_protnone(*pvmw.pte) && pte_savedwrite(*pvmw.pte)) ||
|
|
mm_tlb_flush_pending(mm)) {
|
|
pte_t entry;
|
|
|
|
swapped = PageSwapCache(page);
|
|
flush_cache_page(vma, pvmw.address, page_to_pfn(page));
|
|
/*
|
|
* Ok this is tricky, when get_user_pages_fast() run it doesn't
|
|
* take any lock, therefore the check that we are going to make
|
|
* with the pagecount against the mapcount is racey and
|
|
* O_DIRECT can happen right after the check.
|
|
* So we clear the pte and flush the tlb before the check
|
|
* this assure us that no O_DIRECT can happen after the check
|
|
* or in the middle of the check.
|
|
*
|
|
* No need to notify as we are downgrading page table to read
|
|
* only not changing it to point to a new page.
|
|
*
|
|
* See Documentation/vm/mmu_notifier.txt
|
|
*/
|
|
entry = ptep_clear_flush(vma, pvmw.address, pvmw.pte);
|
|
/*
|
|
* Check that no O_DIRECT or similar I/O is in progress on the
|
|
* page
|
|
*/
|
|
if (page_mapcount(page) + 1 + swapped != page_count(page)) {
|
|
set_pte_at(mm, pvmw.address, pvmw.pte, entry);
|
|
goto out_unlock;
|
|
}
|
|
if (pte_dirty(entry))
|
|
set_page_dirty(page);
|
|
|
|
if (pte_protnone(entry))
|
|
entry = pte_mkclean(pte_clear_savedwrite(entry));
|
|
else
|
|
entry = pte_mkclean(pte_wrprotect(entry));
|
|
set_pte_at_notify(mm, pvmw.address, pvmw.pte, entry);
|
|
}
|
|
*orig_pte = *pvmw.pte;
|
|
err = 0;
|
|
|
|
out_unlock:
|
|
page_vma_mapped_walk_done(&pvmw);
|
|
out_mn:
|
|
mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
|
|
out:
|
|
return err;
|
|
}
|
|
|
|
/**
|
|
* replace_page - replace page in vma by new ksm page
|
|
* @vma: vma that holds the pte pointing to page
|
|
* @page: the page we are replacing by kpage
|
|
* @kpage: the ksm page we replace page by
|
|
* @orig_pte: the original value of the pte
|
|
*
|
|
* Returns 0 on success, -EFAULT on failure.
|
|
*/
|
|
static int replace_page(struct vm_area_struct *vma, struct page *page,
|
|
struct page *kpage, pte_t orig_pte)
|
|
{
|
|
struct mm_struct *mm = vma->vm_mm;
|
|
pmd_t *pmd;
|
|
pte_t *ptep;
|
|
pte_t newpte;
|
|
spinlock_t *ptl;
|
|
unsigned long addr;
|
|
int err = -EFAULT;
|
|
unsigned long mmun_start; /* For mmu_notifiers */
|
|
unsigned long mmun_end; /* For mmu_notifiers */
|
|
|
|
addr = page_address_in_vma(page, vma);
|
|
if (addr == -EFAULT)
|
|
goto out;
|
|
|
|
pmd = mm_find_pmd(mm, addr);
|
|
if (!pmd)
|
|
goto out;
|
|
|
|
mmun_start = addr;
|
|
mmun_end = addr + PAGE_SIZE;
|
|
mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
|
|
|
|
ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
|
|
if (!pte_same(*ptep, orig_pte)) {
|
|
pte_unmap_unlock(ptep, ptl);
|
|
goto out_mn;
|
|
}
|
|
|
|
/*
|
|
* No need to check ksm_use_zero_pages here: we can only have a
|
|
* zero_page here if ksm_use_zero_pages was enabled alreaady.
|
|
*/
|
|
if (!is_zero_pfn(page_to_pfn(kpage))) {
|
|
get_page(kpage);
|
|
page_add_anon_rmap(kpage, vma, addr, false);
|
|
newpte = mk_pte(kpage, vma->vm_page_prot);
|
|
} else {
|
|
newpte = pte_mkspecial(pfn_pte(page_to_pfn(kpage),
|
|
vma->vm_page_prot));
|
|
}
|
|
|
|
flush_cache_page(vma, addr, pte_pfn(*ptep));
|
|
/*
|
|
* No need to notify as we are replacing a read only page with another
|
|
* read only page with the same content.
|
|
*
|
|
* See Documentation/vm/mmu_notifier.txt
|
|
*/
|
|
ptep_clear_flush(vma, addr, ptep);
|
|
set_pte_at_notify(mm, addr, ptep, newpte);
|
|
|
|
page_remove_rmap(page, false);
|
|
if (!page_mapped(page))
|
|
try_to_free_swap(page);
|
|
put_page(page);
|
|
|
|
pte_unmap_unlock(ptep, ptl);
|
|
err = 0;
|
|
out_mn:
|
|
mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
|
|
out:
|
|
return err;
|
|
}
|
|
|
|
/*
|
|
* try_to_merge_one_page - take two pages and merge them into one
|
|
* @vma: the vma that holds the pte pointing to page
|
|
* @page: the PageAnon page that we want to replace with kpage
|
|
* @kpage: the PageKsm page that we want to map instead of page,
|
|
* or NULL the first time when we want to use page as kpage.
|
|
*
|
|
* This function returns 0 if the pages were merged, -EFAULT otherwise.
|
|
*/
|
|
static int try_to_merge_one_page(struct vm_area_struct *vma,
|
|
struct page *page, struct page *kpage)
|
|
{
|
|
pte_t orig_pte = __pte(0);
|
|
int err = -EFAULT;
|
|
|
|
if (page == kpage) /* ksm page forked */
|
|
return 0;
|
|
|
|
if (!PageAnon(page))
|
|
goto out;
|
|
|
|
/*
|
|
* We need the page lock to read a stable PageSwapCache in
|
|
* write_protect_page(). We use trylock_page() instead of
|
|
* lock_page() because we don't want to wait here - we
|
|
* prefer to continue scanning and merging different pages,
|
|
* then come back to this page when it is unlocked.
|
|
*/
|
|
if (!trylock_page(page))
|
|
goto out;
|
|
|
|
if (PageTransCompound(page)) {
|
|
if (split_huge_page(page))
|
|
goto out_unlock;
|
|
}
|
|
|
|
/*
|
|
* If this anonymous page is mapped only here, its pte may need
|
|
* to be write-protected. If it's mapped elsewhere, all of its
|
|
* ptes are necessarily already write-protected. But in either
|
|
* case, we need to lock and check page_count is not raised.
|
|
*/
|
|
if (write_protect_page(vma, page, &orig_pte) == 0) {
|
|
if (!kpage) {
|
|
/*
|
|
* While we hold page lock, upgrade page from
|
|
* PageAnon+anon_vma to PageKsm+NULL stable_node:
|
|
* stable_tree_insert() will update stable_node.
|
|
*/
|
|
set_page_stable_node(page, NULL);
|
|
mark_page_accessed(page);
|
|
/*
|
|
* Page reclaim just frees a clean page with no dirty
|
|
* ptes: make sure that the ksm page would be swapped.
|
|
*/
|
|
if (!PageDirty(page))
|
|
SetPageDirty(page);
|
|
err = 0;
|
|
} else if (pages_identical(page, kpage))
|
|
err = replace_page(vma, page, kpage, orig_pte);
|
|
}
|
|
|
|
if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
|
|
munlock_vma_page(page);
|
|
if (!PageMlocked(kpage)) {
|
|
unlock_page(page);
|
|
lock_page(kpage);
|
|
mlock_vma_page(kpage);
|
|
page = kpage; /* for final unlock */
|
|
}
|
|
}
|
|
|
|
out_unlock:
|
|
unlock_page(page);
|
|
out:
|
|
return err;
|
|
}
|
|
|
|
/*
|
|
* try_to_merge_with_ksm_page - like try_to_merge_two_pages,
|
|
* but no new kernel page is allocated: kpage must already be a ksm page.
|
|
*
|
|
* This function returns 0 if the pages were merged, -EFAULT otherwise.
|
|
*/
|
|
static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
|
|
struct page *page, struct page *kpage)
|
|
{
|
|
struct mm_struct *mm = rmap_item->mm;
|
|
struct vm_area_struct *vma;
|
|
int err = -EFAULT;
|
|
|
|
down_read(&mm->mmap_sem);
|
|
vma = find_mergeable_vma(mm, rmap_item->address);
|
|
if (!vma)
|
|
goto out;
|
|
|
|
err = try_to_merge_one_page(vma, page, kpage);
|
|
if (err)
|
|
goto out;
|
|
|
|
/* Unstable nid is in union with stable anon_vma: remove first */
|
|
remove_rmap_item_from_tree(rmap_item);
|
|
|
|
/* Must get reference to anon_vma while still holding mmap_sem */
|
|
rmap_item->anon_vma = vma->anon_vma;
|
|
get_anon_vma(vma->anon_vma);
|
|
out:
|
|
up_read(&mm->mmap_sem);
|
|
return err;
|
|
}
|
|
|
|
/*
|
|
* try_to_merge_two_pages - take two identical pages and prepare them
|
|
* to be merged into one page.
|
|
*
|
|
* This function returns the kpage if we successfully merged two identical
|
|
* pages into one ksm page, NULL otherwise.
|
|
*
|
|
* Note that this function upgrades page to ksm page: if one of the pages
|
|
* is already a ksm page, try_to_merge_with_ksm_page should be used.
|
|
*/
|
|
static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
|
|
struct page *page,
|
|
struct rmap_item *tree_rmap_item,
|
|
struct page *tree_page)
|
|
{
|
|
int err;
|
|
|
|
err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
|
|
if (!err) {
|
|
err = try_to_merge_with_ksm_page(tree_rmap_item,
|
|
tree_page, page);
|
|
/*
|
|
* If that fails, we have a ksm page with only one pte
|
|
* pointing to it: so break it.
|
|
*/
|
|
if (err)
|
|
break_cow(rmap_item);
|
|
}
|
|
return err ? NULL : page;
|
|
}
|
|
|
|
static __always_inline
|
|
bool __is_page_sharing_candidate(struct stable_node *stable_node, int offset)
|
|
{
|
|
VM_BUG_ON(stable_node->rmap_hlist_len < 0);
|
|
/*
|
|
* Check that at least one mapping still exists, otherwise
|
|
* there's no much point to merge and share with this
|
|
* stable_node, as the underlying tree_page of the other
|
|
* sharer is going to be freed soon.
|
|
*/
|
|
return stable_node->rmap_hlist_len &&
|
|
stable_node->rmap_hlist_len + offset < ksm_max_page_sharing;
|
|
}
|
|
|
|
static __always_inline
|
|
bool is_page_sharing_candidate(struct stable_node *stable_node)
|
|
{
|
|
return __is_page_sharing_candidate(stable_node, 0);
|
|
}
|
|
|
|
struct page *stable_node_dup(struct stable_node **_stable_node_dup,
|
|
struct stable_node **_stable_node,
|
|
struct rb_root *root,
|
|
bool prune_stale_stable_nodes)
|
|
{
|
|
struct stable_node *dup, *found = NULL, *stable_node = *_stable_node;
|
|
struct hlist_node *hlist_safe;
|
|
struct page *_tree_page, *tree_page = NULL;
|
|
int nr = 0;
|
|
int found_rmap_hlist_len;
|
|
|
|
if (!prune_stale_stable_nodes ||
|
|
time_before(jiffies, stable_node->chain_prune_time +
|
|
msecs_to_jiffies(
|
|
ksm_stable_node_chains_prune_millisecs)))
|
|
prune_stale_stable_nodes = false;
|
|
else
|
|
stable_node->chain_prune_time = jiffies;
|
|
|
|
hlist_for_each_entry_safe(dup, hlist_safe,
|
|
&stable_node->hlist, hlist_dup) {
|
|
cond_resched();
|
|
/*
|
|
* We must walk all stable_node_dup to prune the stale
|
|
* stable nodes during lookup.
|
|
*
|
|
* get_ksm_page can drop the nodes from the
|
|
* stable_node->hlist if they point to freed pages
|
|
* (that's why we do a _safe walk). The "dup"
|
|
* stable_node parameter itself will be freed from
|
|
* under us if it returns NULL.
|
|
*/
|
|
_tree_page = get_ksm_page(dup, false);
|
|
if (!_tree_page)
|
|
continue;
|
|
nr += 1;
|
|
if (is_page_sharing_candidate(dup)) {
|
|
if (!found ||
|
|
dup->rmap_hlist_len > found_rmap_hlist_len) {
|
|
if (found)
|
|
put_page(tree_page);
|
|
found = dup;
|
|
found_rmap_hlist_len = found->rmap_hlist_len;
|
|
tree_page = _tree_page;
|
|
|
|
/* skip put_page for found dup */
|
|
if (!prune_stale_stable_nodes)
|
|
break;
|
|
continue;
|
|
}
|
|
}
|
|
put_page(_tree_page);
|
|
}
|
|
|
|
if (found) {
|
|
/*
|
|
* nr is counting all dups in the chain only if
|
|
* prune_stale_stable_nodes is true, otherwise we may
|
|
* break the loop at nr == 1 even if there are
|
|
* multiple entries.
|
|
*/
|
|
if (prune_stale_stable_nodes && nr == 1) {
|
|
/*
|
|
* If there's not just one entry it would
|
|
* corrupt memory, better BUG_ON. In KSM
|
|
* context with no lock held it's not even
|
|
* fatal.
|
|
*/
|
|
BUG_ON(stable_node->hlist.first->next);
|
|
|
|
/*
|
|
* There's just one entry and it is below the
|
|
* deduplication limit so drop the chain.
|
|
*/
|
|
rb_replace_node(&stable_node->node, &found->node,
|
|
root);
|
|
free_stable_node(stable_node);
|
|
ksm_stable_node_chains--;
|
|
ksm_stable_node_dups--;
|
|
/*
|
|
* NOTE: the caller depends on the stable_node
|
|
* to be equal to stable_node_dup if the chain
|
|
* was collapsed.
|
|
*/
|
|
*_stable_node = found;
|
|
/*
|
|
* Just for robustneess as stable_node is
|
|
* otherwise left as a stable pointer, the
|
|
* compiler shall optimize it away at build
|
|
* time.
|
|
*/
|
|
stable_node = NULL;
|
|
} else if (stable_node->hlist.first != &found->hlist_dup &&
|
|
__is_page_sharing_candidate(found, 1)) {
|
|
/*
|
|
* If the found stable_node dup can accept one
|
|
* more future merge (in addition to the one
|
|
* that is underway) and is not at the head of
|
|
* the chain, put it there so next search will
|
|
* be quicker in the !prune_stale_stable_nodes
|
|
* case.
|
|
*
|
|
* NOTE: it would be inaccurate to use nr > 1
|
|
* instead of checking the hlist.first pointer
|
|
* directly, because in the
|
|
* prune_stale_stable_nodes case "nr" isn't
|
|
* the position of the found dup in the chain,
|
|
* but the total number of dups in the chain.
|
|
*/
|
|
hlist_del(&found->hlist_dup);
|
|
hlist_add_head(&found->hlist_dup,
|
|
&stable_node->hlist);
|
|
}
|
|
}
|
|
|
|
*_stable_node_dup = found;
|
|
return tree_page;
|
|
}
|
|
|
|
static struct stable_node *stable_node_dup_any(struct stable_node *stable_node,
|
|
struct rb_root *root)
|
|
{
|
|
if (!is_stable_node_chain(stable_node))
|
|
return stable_node;
|
|
if (hlist_empty(&stable_node->hlist)) {
|
|
free_stable_node_chain(stable_node, root);
|
|
return NULL;
|
|
}
|
|
return hlist_entry(stable_node->hlist.first,
|
|
typeof(*stable_node), hlist_dup);
|
|
}
|
|
|
|
/*
|
|
* Like for get_ksm_page, this function can free the *_stable_node and
|
|
* *_stable_node_dup if the returned tree_page is NULL.
|
|
*
|
|
* It can also free and overwrite *_stable_node with the found
|
|
* stable_node_dup if the chain is collapsed (in which case
|
|
* *_stable_node will be equal to *_stable_node_dup like if the chain
|
|
* never existed). It's up to the caller to verify tree_page is not
|
|
* NULL before dereferencing *_stable_node or *_stable_node_dup.
|
|
*
|
|
* *_stable_node_dup is really a second output parameter of this
|
|
* function and will be overwritten in all cases, the caller doesn't
|
|
* need to initialize it.
|
|
*/
|
|
static struct page *__stable_node_chain(struct stable_node **_stable_node_dup,
|
|
struct stable_node **_stable_node,
|
|
struct rb_root *root,
|
|
bool prune_stale_stable_nodes)
|
|
{
|
|
struct stable_node *stable_node = *_stable_node;
|
|
if (!is_stable_node_chain(stable_node)) {
|
|
if (is_page_sharing_candidate(stable_node)) {
|
|
*_stable_node_dup = stable_node;
|
|
return get_ksm_page(stable_node, false);
|
|
}
|
|
/*
|
|
* _stable_node_dup set to NULL means the stable_node
|
|
* reached the ksm_max_page_sharing limit.
|
|
*/
|
|
*_stable_node_dup = NULL;
|
|
return NULL;
|
|
}
|
|
return stable_node_dup(_stable_node_dup, _stable_node, root,
|
|
prune_stale_stable_nodes);
|
|
}
|
|
|
|
static __always_inline struct page *chain_prune(struct stable_node **s_n_d,
|
|
struct stable_node **s_n,
|
|
struct rb_root *root)
|
|
{
|
|
return __stable_node_chain(s_n_d, s_n, root, true);
|
|
}
|
|
|
|
static __always_inline struct page *chain(struct stable_node **s_n_d,
|
|
struct stable_node *s_n,
|
|
struct rb_root *root)
|
|
{
|
|
struct stable_node *old_stable_node = s_n;
|
|
struct page *tree_page;
|
|
|
|
tree_page = __stable_node_chain(s_n_d, &s_n, root, false);
|
|
/* not pruning dups so s_n cannot have changed */
|
|
VM_BUG_ON(s_n != old_stable_node);
|
|
return tree_page;
|
|
}
|
|
|
|
/*
|
|
* stable_tree_search - search for page inside the stable tree
|
|
*
|
|
* This function checks if there is a page inside the stable tree
|
|
* with identical content to the page that we are scanning right now.
|
|
*
|
|
* This function returns the stable tree node of identical content if found,
|
|
* NULL otherwise.
|
|
*/
|
|
static struct page *stable_tree_search(struct page *page)
|
|
{
|
|
int nid;
|
|
struct rb_root *root;
|
|
struct rb_node **new;
|
|
struct rb_node *parent;
|
|
struct stable_node *stable_node, *stable_node_dup, *stable_node_any;
|
|
struct stable_node *page_node;
|
|
|
|
page_node = page_stable_node(page);
|
|
if (page_node && page_node->head != &migrate_nodes) {
|
|
/* ksm page forked */
|
|
get_page(page);
|
|
return page;
|
|
}
|
|
|
|
nid = get_kpfn_nid(page_to_pfn(page));
|
|
root = root_stable_tree + nid;
|
|
again:
|
|
new = &root->rb_node;
|
|
parent = NULL;
|
|
|
|
while (*new) {
|
|
struct page *tree_page;
|
|
int ret;
|
|
|
|
cond_resched();
|
|
stable_node = rb_entry(*new, struct stable_node, node);
|
|
stable_node_any = NULL;
|
|
tree_page = chain_prune(&stable_node_dup, &stable_node, root);
|
|
/*
|
|
* NOTE: stable_node may have been freed by
|
|
* chain_prune() if the returned stable_node_dup is
|
|
* not NULL. stable_node_dup may have been inserted in
|
|
* the rbtree instead as a regular stable_node (in
|
|
* order to collapse the stable_node chain if a single
|
|
* stable_node dup was found in it). In such case the
|
|
* stable_node is overwritten by the calleee to point
|
|
* to the stable_node_dup that was collapsed in the
|
|
* stable rbtree and stable_node will be equal to
|
|
* stable_node_dup like if the chain never existed.
|
|
*/
|
|
if (!stable_node_dup) {
|
|
/*
|
|
* Either all stable_node dups were full in
|
|
* this stable_node chain, or this chain was
|
|
* empty and should be rb_erased.
|
|
*/
|
|
stable_node_any = stable_node_dup_any(stable_node,
|
|
root);
|
|
if (!stable_node_any) {
|
|
/* rb_erase just run */
|
|
goto again;
|
|
}
|
|
/*
|
|
* Take any of the stable_node dups page of
|
|
* this stable_node chain to let the tree walk
|
|
* continue. All KSM pages belonging to the
|
|
* stable_node dups in a stable_node chain
|
|
* have the same content and they're
|
|
* wrprotected at all times. Any will work
|
|
* fine to continue the walk.
|
|
*/
|
|
tree_page = get_ksm_page(stable_node_any, false);
|
|
}
|
|
VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
|
|
if (!tree_page) {
|
|
/*
|
|
* If we walked over a stale stable_node,
|
|
* get_ksm_page() will call rb_erase() and it
|
|
* may rebalance the tree from under us. So
|
|
* restart the search from scratch. Returning
|
|
* NULL would be safe too, but we'd generate
|
|
* false negative insertions just because some
|
|
* stable_node was stale.
|
|
*/
|
|
goto again;
|
|
}
|
|
|
|
ret = memcmp_pages(page, tree_page);
|
|
put_page(tree_page);
|
|
|
|
parent = *new;
|
|
if (ret < 0)
|
|
new = &parent->rb_left;
|
|
else if (ret > 0)
|
|
new = &parent->rb_right;
|
|
else {
|
|
if (page_node) {
|
|
VM_BUG_ON(page_node->head != &migrate_nodes);
|
|
/*
|
|
* Test if the migrated page should be merged
|
|
* into a stable node dup. If the mapcount is
|
|
* 1 we can migrate it with another KSM page
|
|
* without adding it to the chain.
|
|
*/
|
|
if (page_mapcount(page) > 1)
|
|
goto chain_append;
|
|
}
|
|
|
|
if (!stable_node_dup) {
|
|
/*
|
|
* If the stable_node is a chain and
|
|
* we got a payload match in memcmp
|
|
* but we cannot merge the scanned
|
|
* page in any of the existing
|
|
* stable_node dups because they're
|
|
* all full, we need to wait the
|
|
* scanned page to find itself a match
|
|
* in the unstable tree to create a
|
|
* brand new KSM page to add later to
|
|
* the dups of this stable_node.
|
|
*/
|
|
return NULL;
|
|
}
|
|
|
|
/*
|
|
* Lock and unlock the stable_node's page (which
|
|
* might already have been migrated) so that page
|
|
* migration is sure to notice its raised count.
|
|
* It would be more elegant to return stable_node
|
|
* than kpage, but that involves more changes.
|
|
*/
|
|
tree_page = get_ksm_page(stable_node_dup, true);
|
|
if (unlikely(!tree_page))
|
|
/*
|
|
* The tree may have been rebalanced,
|
|
* so re-evaluate parent and new.
|
|
*/
|
|
goto again;
|
|
unlock_page(tree_page);
|
|
|
|
if (get_kpfn_nid(stable_node_dup->kpfn) !=
|
|
NUMA(stable_node_dup->nid)) {
|
|
put_page(tree_page);
|
|
goto replace;
|
|
}
|
|
return tree_page;
|
|
}
|
|
}
|
|
|
|
if (!page_node)
|
|
return NULL;
|
|
|
|
list_del(&page_node->list);
|
|
DO_NUMA(page_node->nid = nid);
|
|
rb_link_node(&page_node->node, parent, new);
|
|
rb_insert_color(&page_node->node, root);
|
|
out:
|
|
if (is_page_sharing_candidate(page_node)) {
|
|
get_page(page);
|
|
return page;
|
|
} else
|
|
return NULL;
|
|
|
|
replace:
|
|
/*
|
|
* If stable_node was a chain and chain_prune collapsed it,
|
|
* stable_node has been updated to be the new regular
|
|
* stable_node. A collapse of the chain is indistinguishable
|
|
* from the case there was no chain in the stable
|
|
* rbtree. Otherwise stable_node is the chain and
|
|
* stable_node_dup is the dup to replace.
|
|
*/
|
|
if (stable_node_dup == stable_node) {
|
|
VM_BUG_ON(is_stable_node_chain(stable_node_dup));
|
|
VM_BUG_ON(is_stable_node_dup(stable_node_dup));
|
|
/* there is no chain */
|
|
if (page_node) {
|
|
VM_BUG_ON(page_node->head != &migrate_nodes);
|
|
list_del(&page_node->list);
|
|
DO_NUMA(page_node->nid = nid);
|
|
rb_replace_node(&stable_node_dup->node,
|
|
&page_node->node,
|
|
root);
|
|
if (is_page_sharing_candidate(page_node))
|
|
get_page(page);
|
|
else
|
|
page = NULL;
|
|
} else {
|
|
rb_erase(&stable_node_dup->node, root);
|
|
page = NULL;
|
|
}
|
|
} else {
|
|
VM_BUG_ON(!is_stable_node_chain(stable_node));
|
|
__stable_node_dup_del(stable_node_dup);
|
|
if (page_node) {
|
|
VM_BUG_ON(page_node->head != &migrate_nodes);
|
|
list_del(&page_node->list);
|
|
DO_NUMA(page_node->nid = nid);
|
|
stable_node_chain_add_dup(page_node, stable_node);
|
|
if (is_page_sharing_candidate(page_node))
|
|
get_page(page);
|
|
else
|
|
page = NULL;
|
|
} else {
|
|
page = NULL;
|
|
}
|
|
}
|
|
stable_node_dup->head = &migrate_nodes;
|
|
list_add(&stable_node_dup->list, stable_node_dup->head);
|
|
return page;
|
|
|
|
chain_append:
|
|
/* stable_node_dup could be null if it reached the limit */
|
|
if (!stable_node_dup)
|
|
stable_node_dup = stable_node_any;
|
|
/*
|
|
* If stable_node was a chain and chain_prune collapsed it,
|
|
* stable_node has been updated to be the new regular
|
|
* stable_node. A collapse of the chain is indistinguishable
|
|
* from the case there was no chain in the stable
|
|
* rbtree. Otherwise stable_node is the chain and
|
|
* stable_node_dup is the dup to replace.
|
|
*/
|
|
if (stable_node_dup == stable_node) {
|
|
VM_BUG_ON(is_stable_node_chain(stable_node_dup));
|
|
VM_BUG_ON(is_stable_node_dup(stable_node_dup));
|
|
/* chain is missing so create it */
|
|
stable_node = alloc_stable_node_chain(stable_node_dup,
|
|
root);
|
|
if (!stable_node)
|
|
return NULL;
|
|
}
|
|
/*
|
|
* Add this stable_node dup that was
|
|
* migrated to the stable_node chain
|
|
* of the current nid for this page
|
|
* content.
|
|
*/
|
|
VM_BUG_ON(!is_stable_node_chain(stable_node));
|
|
VM_BUG_ON(!is_stable_node_dup(stable_node_dup));
|
|
VM_BUG_ON(page_node->head != &migrate_nodes);
|
|
list_del(&page_node->list);
|
|
DO_NUMA(page_node->nid = nid);
|
|
stable_node_chain_add_dup(page_node, stable_node);
|
|
goto out;
|
|
}
|
|
|
|
/*
|
|
* stable_tree_insert - insert stable tree node pointing to new ksm page
|
|
* into the stable tree.
|
|
*
|
|
* This function returns the stable tree node just allocated on success,
|
|
* NULL otherwise.
|
|
*/
|
|
static struct stable_node *stable_tree_insert(struct page *kpage)
|
|
{
|
|
int nid;
|
|
unsigned long kpfn;
|
|
struct rb_root *root;
|
|
struct rb_node **new;
|
|
struct rb_node *parent;
|
|
struct stable_node *stable_node, *stable_node_dup, *stable_node_any;
|
|
bool need_chain = false;
|
|
|
|
kpfn = page_to_pfn(kpage);
|
|
nid = get_kpfn_nid(kpfn);
|
|
root = root_stable_tree + nid;
|
|
again:
|
|
parent = NULL;
|
|
new = &root->rb_node;
|
|
|
|
while (*new) {
|
|
struct page *tree_page;
|
|
int ret;
|
|
|
|
cond_resched();
|
|
stable_node = rb_entry(*new, struct stable_node, node);
|
|
stable_node_any = NULL;
|
|
tree_page = chain(&stable_node_dup, stable_node, root);
|
|
if (!stable_node_dup) {
|
|
/*
|
|
* Either all stable_node dups were full in
|
|
* this stable_node chain, or this chain was
|
|
* empty and should be rb_erased.
|
|
*/
|
|
stable_node_any = stable_node_dup_any(stable_node,
|
|
root);
|
|
if (!stable_node_any) {
|
|
/* rb_erase just run */
|
|
goto again;
|
|
}
|
|
/*
|
|
* Take any of the stable_node dups page of
|
|
* this stable_node chain to let the tree walk
|
|
* continue. All KSM pages belonging to the
|
|
* stable_node dups in a stable_node chain
|
|
* have the same content and they're
|
|
* wrprotected at all times. Any will work
|
|
* fine to continue the walk.
|
|
*/
|
|
tree_page = get_ksm_page(stable_node_any, false);
|
|
}
|
|
VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
|
|
if (!tree_page) {
|
|
/*
|
|
* If we walked over a stale stable_node,
|
|
* get_ksm_page() will call rb_erase() and it
|
|
* may rebalance the tree from under us. So
|
|
* restart the search from scratch. Returning
|
|
* NULL would be safe too, but we'd generate
|
|
* false negative insertions just because some
|
|
* stable_node was stale.
|
|
*/
|
|
goto again;
|
|
}
|
|
|
|
ret = memcmp_pages(kpage, tree_page);
|
|
put_page(tree_page);
|
|
|
|
parent = *new;
|
|
if (ret < 0)
|
|
new = &parent->rb_left;
|
|
else if (ret > 0)
|
|
new = &parent->rb_right;
|
|
else {
|
|
need_chain = true;
|
|
break;
|
|
}
|
|
}
|
|
|
|
stable_node_dup = alloc_stable_node();
|
|
if (!stable_node_dup)
|
|
return NULL;
|
|
|
|
INIT_HLIST_HEAD(&stable_node_dup->hlist);
|
|
stable_node_dup->kpfn = kpfn;
|
|
set_page_stable_node(kpage, stable_node_dup);
|
|
stable_node_dup->rmap_hlist_len = 0;
|
|
DO_NUMA(stable_node_dup->nid = nid);
|
|
if (!need_chain) {
|
|
rb_link_node(&stable_node_dup->node, parent, new);
|
|
rb_insert_color(&stable_node_dup->node, root);
|
|
} else {
|
|
if (!is_stable_node_chain(stable_node)) {
|
|
struct stable_node *orig = stable_node;
|
|
/* chain is missing so create it */
|
|
stable_node = alloc_stable_node_chain(orig, root);
|
|
if (!stable_node) {
|
|
free_stable_node(stable_node_dup);
|
|
return NULL;
|
|
}
|
|
}
|
|
stable_node_chain_add_dup(stable_node_dup, stable_node);
|
|
}
|
|
|
|
return stable_node_dup;
|
|
}
|
|
|
|
/*
|
|
* unstable_tree_search_insert - search for identical page,
|
|
* else insert rmap_item into the unstable tree.
|
|
*
|
|
* This function searches for a page in the unstable tree identical to the
|
|
* page currently being scanned; and if no identical page is found in the
|
|
* tree, we insert rmap_item as a new object into the unstable tree.
|
|
*
|
|
* This function returns pointer to rmap_item found to be identical
|
|
* to the currently scanned page, NULL otherwise.
|
|
*
|
|
* This function does both searching and inserting, because they share
|
|
* the same walking algorithm in an rbtree.
|
|
*/
|
|
static
|
|
struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
|
|
struct page *page,
|
|
struct page **tree_pagep)
|
|
{
|
|
struct rb_node **new;
|
|
struct rb_root *root;
|
|
struct rb_node *parent = NULL;
|
|
int nid;
|
|
|
|
nid = get_kpfn_nid(page_to_pfn(page));
|
|
root = root_unstable_tree + nid;
|
|
new = &root->rb_node;
|
|
|
|
while (*new) {
|
|
struct rmap_item *tree_rmap_item;
|
|
struct page *tree_page;
|
|
int ret;
|
|
|
|
cond_resched();
|
|
tree_rmap_item = rb_entry(*new, struct rmap_item, node);
|
|
tree_page = get_mergeable_page(tree_rmap_item);
|
|
if (!tree_page)
|
|
return NULL;
|
|
|
|
/*
|
|
* Don't substitute a ksm page for a forked page.
|
|
*/
|
|
if (page == tree_page) {
|
|
put_page(tree_page);
|
|
return NULL;
|
|
}
|
|
|
|
ret = memcmp_pages(page, tree_page);
|
|
|
|
parent = *new;
|
|
if (ret < 0) {
|
|
put_page(tree_page);
|
|
new = &parent->rb_left;
|
|
} else if (ret > 0) {
|
|
put_page(tree_page);
|
|
new = &parent->rb_right;
|
|
} else if (!ksm_merge_across_nodes &&
|
|
page_to_nid(tree_page) != nid) {
|
|
/*
|
|
* If tree_page has been migrated to another NUMA node,
|
|
* it will be flushed out and put in the right unstable
|
|
* tree next time: only merge with it when across_nodes.
|
|
*/
|
|
put_page(tree_page);
|
|
return NULL;
|
|
} else {
|
|
*tree_pagep = tree_page;
|
|
return tree_rmap_item;
|
|
}
|
|
}
|
|
|
|
rmap_item->address |= UNSTABLE_FLAG;
|
|
rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
|
|
DO_NUMA(rmap_item->nid = nid);
|
|
rb_link_node(&rmap_item->node, parent, new);
|
|
rb_insert_color(&rmap_item->node, root);
|
|
|
|
ksm_pages_unshared++;
|
|
return NULL;
|
|
}
|
|
|
|
/*
|
|
* stable_tree_append - add another rmap_item to the linked list of
|
|
* rmap_items hanging off a given node of the stable tree, all sharing
|
|
* the same ksm page.
|
|
*/
|
|
static void stable_tree_append(struct rmap_item *rmap_item,
|
|
struct stable_node *stable_node,
|
|
bool max_page_sharing_bypass)
|
|
{
|
|
/*
|
|
* rmap won't find this mapping if we don't insert the
|
|
* rmap_item in the right stable_node
|
|
* duplicate. page_migration could break later if rmap breaks,
|
|
* so we can as well crash here. We really need to check for
|
|
* rmap_hlist_len == STABLE_NODE_CHAIN, but we can as well check
|
|
* for other negative values as an undeflow if detected here
|
|
* for the first time (and not when decreasing rmap_hlist_len)
|
|
* would be sign of memory corruption in the stable_node.
|
|
*/
|
|
BUG_ON(stable_node->rmap_hlist_len < 0);
|
|
|
|
stable_node->rmap_hlist_len++;
|
|
if (!max_page_sharing_bypass)
|
|
/* possibly non fatal but unexpected overflow, only warn */
|
|
WARN_ON_ONCE(stable_node->rmap_hlist_len >
|
|
ksm_max_page_sharing);
|
|
|
|
rmap_item->head = stable_node;
|
|
rmap_item->address |= STABLE_FLAG;
|
|
hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
|
|
|
|
if (rmap_item->hlist.next)
|
|
ksm_pages_sharing++;
|
|
else
|
|
ksm_pages_shared++;
|
|
}
|
|
|
|
/*
|
|
* cmp_and_merge_page - first see if page can be merged into the stable tree;
|
|
* if not, compare checksum to previous and if it's the same, see if page can
|
|
* be inserted into the unstable tree, or merged with a page already there and
|
|
* both transferred to the stable tree.
|
|
*
|
|
* @page: the page that we are searching identical page to.
|
|
* @rmap_item: the reverse mapping into the virtual address of this page
|
|
*/
|
|
static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
|
|
{
|
|
struct mm_struct *mm = rmap_item->mm;
|
|
struct rmap_item *tree_rmap_item;
|
|
struct page *tree_page = NULL;
|
|
struct stable_node *stable_node;
|
|
struct page *kpage;
|
|
unsigned int checksum;
|
|
int err;
|
|
bool max_page_sharing_bypass = false;
|
|
|
|
stable_node = page_stable_node(page);
|
|
if (stable_node) {
|
|
if (stable_node->head != &migrate_nodes &&
|
|
get_kpfn_nid(READ_ONCE(stable_node->kpfn)) !=
|
|
NUMA(stable_node->nid)) {
|
|
stable_node_dup_del(stable_node);
|
|
stable_node->head = &migrate_nodes;
|
|
list_add(&stable_node->list, stable_node->head);
|
|
}
|
|
if (stable_node->head != &migrate_nodes &&
|
|
rmap_item->head == stable_node)
|
|
return;
|
|
/*
|
|
* If it's a KSM fork, allow it to go over the sharing limit
|
|
* without warnings.
|
|
*/
|
|
if (!is_page_sharing_candidate(stable_node))
|
|
max_page_sharing_bypass = true;
|
|
}
|
|
|
|
/* We first start with searching the page inside the stable tree */
|
|
kpage = stable_tree_search(page);
|
|
if (kpage == page && rmap_item->head == stable_node) {
|
|
put_page(kpage);
|
|
return;
|
|
}
|
|
|
|
remove_rmap_item_from_tree(rmap_item);
|
|
|
|
if (kpage) {
|
|
err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
|
|
if (!err) {
|
|
/*
|
|
* The page was successfully merged:
|
|
* add its rmap_item to the stable tree.
|
|
*/
|
|
lock_page(kpage);
|
|
stable_tree_append(rmap_item, page_stable_node(kpage),
|
|
max_page_sharing_bypass);
|
|
unlock_page(kpage);
|
|
}
|
|
put_page(kpage);
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* If the hash value of the page has changed from the last time
|
|
* we calculated it, this page is changing frequently: therefore we
|
|
* don't want to insert it in the unstable tree, and we don't want
|
|
* to waste our time searching for something identical to it there.
|
|
*/
|
|
checksum = calc_checksum(page);
|
|
if (rmap_item->oldchecksum != checksum) {
|
|
rmap_item->oldchecksum = checksum;
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* Same checksum as an empty page. We attempt to merge it with the
|
|
* appropriate zero page if the user enabled this via sysfs.
|
|
*/
|
|
if (ksm_use_zero_pages && (checksum == zero_checksum)) {
|
|
struct vm_area_struct *vma;
|
|
|
|
down_read(&mm->mmap_sem);
|
|
vma = find_mergeable_vma(mm, rmap_item->address);
|
|
err = try_to_merge_one_page(vma, page,
|
|
ZERO_PAGE(rmap_item->address));
|
|
up_read(&mm->mmap_sem);
|
|
/*
|
|
* In case of failure, the page was not really empty, so we
|
|
* need to continue. Otherwise we're done.
|
|
*/
|
|
if (!err)
|
|
return;
|
|
}
|
|
tree_rmap_item =
|
|
unstable_tree_search_insert(rmap_item, page, &tree_page);
|
|
if (tree_rmap_item) {
|
|
kpage = try_to_merge_two_pages(rmap_item, page,
|
|
tree_rmap_item, tree_page);
|
|
put_page(tree_page);
|
|
if (kpage) {
|
|
/*
|
|
* The pages were successfully merged: insert new
|
|
* node in the stable tree and add both rmap_items.
|
|
*/
|
|
lock_page(kpage);
|
|
stable_node = stable_tree_insert(kpage);
|
|
if (stable_node) {
|
|
stable_tree_append(tree_rmap_item, stable_node,
|
|
false);
|
|
stable_tree_append(rmap_item, stable_node,
|
|
false);
|
|
}
|
|
unlock_page(kpage);
|
|
|
|
/*
|
|
* If we fail to insert the page into the stable tree,
|
|
* we will have 2 virtual addresses that are pointing
|
|
* to a ksm page left outside the stable tree,
|
|
* in which case we need to break_cow on both.
|
|
*/
|
|
if (!stable_node) {
|
|
break_cow(tree_rmap_item);
|
|
break_cow(rmap_item);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
|
|
struct rmap_item **rmap_list,
|
|
unsigned long addr)
|
|
{
|
|
struct rmap_item *rmap_item;
|
|
|
|
while (*rmap_list) {
|
|
rmap_item = *rmap_list;
|
|
if ((rmap_item->address & PAGE_MASK) == addr)
|
|
return rmap_item;
|
|
if (rmap_item->address > addr)
|
|
break;
|
|
*rmap_list = rmap_item->rmap_list;
|
|
remove_rmap_item_from_tree(rmap_item);
|
|
free_rmap_item(rmap_item);
|
|
}
|
|
|
|
rmap_item = alloc_rmap_item();
|
|
if (rmap_item) {
|
|
/* It has already been zeroed */
|
|
rmap_item->mm = mm_slot->mm;
|
|
rmap_item->address = addr;
|
|
rmap_item->rmap_list = *rmap_list;
|
|
*rmap_list = rmap_item;
|
|
}
|
|
return rmap_item;
|
|
}
|
|
|
|
static struct rmap_item *scan_get_next_rmap_item(struct page **page)
|
|
{
|
|
struct mm_struct *mm;
|
|
struct mm_slot *slot;
|
|
struct vm_area_struct *vma;
|
|
struct rmap_item *rmap_item;
|
|
int nid;
|
|
|
|
if (list_empty(&ksm_mm_head.mm_list))
|
|
return NULL;
|
|
|
|
slot = ksm_scan.mm_slot;
|
|
if (slot == &ksm_mm_head) {
|
|
/*
|
|
* A number of pages can hang around indefinitely on per-cpu
|
|
* pagevecs, raised page count preventing write_protect_page
|
|
* from merging them. Though it doesn't really matter much,
|
|
* it is puzzling to see some stuck in pages_volatile until
|
|
* other activity jostles them out, and they also prevented
|
|
* LTP's KSM test from succeeding deterministically; so drain
|
|
* them here (here rather than on entry to ksm_do_scan(),
|
|
* so we don't IPI too often when pages_to_scan is set low).
|
|
*/
|
|
lru_add_drain_all();
|
|
|
|
/*
|
|
* Whereas stale stable_nodes on the stable_tree itself
|
|
* get pruned in the regular course of stable_tree_search(),
|
|
* those moved out to the migrate_nodes list can accumulate:
|
|
* so prune them once before each full scan.
|
|
*/
|
|
if (!ksm_merge_across_nodes) {
|
|
struct stable_node *stable_node, *next;
|
|
struct page *page;
|
|
|
|
list_for_each_entry_safe(stable_node, next,
|
|
&migrate_nodes, list) {
|
|
page = get_ksm_page(stable_node, false);
|
|
if (page)
|
|
put_page(page);
|
|
cond_resched();
|
|
}
|
|
}
|
|
|
|
for (nid = 0; nid < ksm_nr_node_ids; nid++)
|
|
root_unstable_tree[nid] = RB_ROOT;
|
|
|
|
spin_lock(&ksm_mmlist_lock);
|
|
slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
|
|
ksm_scan.mm_slot = slot;
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
/*
|
|
* Although we tested list_empty() above, a racing __ksm_exit
|
|
* of the last mm on the list may have removed it since then.
|
|
*/
|
|
if (slot == &ksm_mm_head)
|
|
return NULL;
|
|
next_mm:
|
|
ksm_scan.address = 0;
|
|
ksm_scan.rmap_list = &slot->rmap_list;
|
|
}
|
|
|
|
mm = slot->mm;
|
|
down_read(&mm->mmap_sem);
|
|
if (ksm_test_exit(mm))
|
|
vma = NULL;
|
|
else
|
|
vma = find_vma(mm, ksm_scan.address);
|
|
|
|
for (; vma; vma = vma->vm_next) {
|
|
if (!(vma->vm_flags & VM_MERGEABLE))
|
|
continue;
|
|
if (ksm_scan.address < vma->vm_start)
|
|
ksm_scan.address = vma->vm_start;
|
|
if (!vma->anon_vma)
|
|
ksm_scan.address = vma->vm_end;
|
|
|
|
while (ksm_scan.address < vma->vm_end) {
|
|
if (ksm_test_exit(mm))
|
|
break;
|
|
*page = follow_page(vma, ksm_scan.address, FOLL_GET);
|
|
if (IS_ERR_OR_NULL(*page)) {
|
|
ksm_scan.address += PAGE_SIZE;
|
|
cond_resched();
|
|
continue;
|
|
}
|
|
if (PageAnon(*page)) {
|
|
flush_anon_page(vma, *page, ksm_scan.address);
|
|
flush_dcache_page(*page);
|
|
rmap_item = get_next_rmap_item(slot,
|
|
ksm_scan.rmap_list, ksm_scan.address);
|
|
if (rmap_item) {
|
|
ksm_scan.rmap_list =
|
|
&rmap_item->rmap_list;
|
|
ksm_scan.address += PAGE_SIZE;
|
|
} else
|
|
put_page(*page);
|
|
up_read(&mm->mmap_sem);
|
|
return rmap_item;
|
|
}
|
|
put_page(*page);
|
|
ksm_scan.address += PAGE_SIZE;
|
|
cond_resched();
|
|
}
|
|
}
|
|
|
|
if (ksm_test_exit(mm)) {
|
|
ksm_scan.address = 0;
|
|
ksm_scan.rmap_list = &slot->rmap_list;
|
|
}
|
|
/*
|
|
* Nuke all the rmap_items that are above this current rmap:
|
|
* because there were no VM_MERGEABLE vmas with such addresses.
|
|
*/
|
|
remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
|
|
|
|
spin_lock(&ksm_mmlist_lock);
|
|
ksm_scan.mm_slot = list_entry(slot->mm_list.next,
|
|
struct mm_slot, mm_list);
|
|
if (ksm_scan.address == 0) {
|
|
/*
|
|
* We've completed a full scan of all vmas, holding mmap_sem
|
|
* throughout, and found no VM_MERGEABLE: so do the same as
|
|
* __ksm_exit does to remove this mm from all our lists now.
|
|
* This applies either when cleaning up after __ksm_exit
|
|
* (but beware: we can reach here even before __ksm_exit),
|
|
* or when all VM_MERGEABLE areas have been unmapped (and
|
|
* mmap_sem then protects against race with MADV_MERGEABLE).
|
|
*/
|
|
hash_del(&slot->link);
|
|
list_del(&slot->mm_list);
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
|
|
free_mm_slot(slot);
|
|
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
|
|
up_read(&mm->mmap_sem);
|
|
mmdrop(mm);
|
|
} else {
|
|
up_read(&mm->mmap_sem);
|
|
/*
|
|
* up_read(&mm->mmap_sem) first because after
|
|
* spin_unlock(&ksm_mmlist_lock) run, the "mm" may
|
|
* already have been freed under us by __ksm_exit()
|
|
* because the "mm_slot" is still hashed and
|
|
* ksm_scan.mm_slot doesn't point to it anymore.
|
|
*/
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
}
|
|
|
|
/* Repeat until we've completed scanning the whole list */
|
|
slot = ksm_scan.mm_slot;
|
|
if (slot != &ksm_mm_head)
|
|
goto next_mm;
|
|
|
|
ksm_scan.seqnr++;
|
|
return NULL;
|
|
}
|
|
|
|
/**
|
|
* ksm_do_scan - the ksm scanner main worker function.
|
|
* @scan_npages - number of pages we want to scan before we return.
|
|
*/
|
|
static void ksm_do_scan(unsigned int scan_npages)
|
|
{
|
|
struct rmap_item *rmap_item;
|
|
struct page *uninitialized_var(page);
|
|
|
|
while (scan_npages-- && likely(!freezing(current))) {
|
|
cond_resched();
|
|
rmap_item = scan_get_next_rmap_item(&page);
|
|
if (!rmap_item)
|
|
return;
|
|
cmp_and_merge_page(page, rmap_item);
|
|
put_page(page);
|
|
}
|
|
}
|
|
|
|
static int ksmd_should_run(void)
|
|
{
|
|
return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
|
|
}
|
|
|
|
static int ksm_scan_thread(void *nothing)
|
|
{
|
|
set_freezable();
|
|
set_user_nice(current, 5);
|
|
|
|
while (!kthread_should_stop()) {
|
|
mutex_lock(&ksm_thread_mutex);
|
|
wait_while_offlining();
|
|
if (ksmd_should_run())
|
|
ksm_do_scan(ksm_thread_pages_to_scan);
|
|
mutex_unlock(&ksm_thread_mutex);
|
|
|
|
try_to_freeze();
|
|
|
|
if (ksmd_should_run()) {
|
|
schedule_timeout_interruptible(
|
|
msecs_to_jiffies(ksm_thread_sleep_millisecs));
|
|
} else {
|
|
wait_event_freezable(ksm_thread_wait,
|
|
ksmd_should_run() || kthread_should_stop());
|
|
}
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
|
|
unsigned long end, int advice, unsigned long *vm_flags)
|
|
{
|
|
struct mm_struct *mm = vma->vm_mm;
|
|
int err;
|
|
|
|
switch (advice) {
|
|
case MADV_MERGEABLE:
|
|
/*
|
|
* Be somewhat over-protective for now!
|
|
*/
|
|
if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
|
|
VM_PFNMAP | VM_IO | VM_DONTEXPAND |
|
|
VM_HUGETLB | VM_MIXEDMAP))
|
|
return 0; /* just ignore the advice */
|
|
|
|
#ifdef VM_SAO
|
|
if (*vm_flags & VM_SAO)
|
|
return 0;
|
|
#endif
|
|
|
|
if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
|
|
err = __ksm_enter(mm);
|
|
if (err)
|
|
return err;
|
|
}
|
|
|
|
*vm_flags |= VM_MERGEABLE;
|
|
break;
|
|
|
|
case MADV_UNMERGEABLE:
|
|
if (!(*vm_flags & VM_MERGEABLE))
|
|
return 0; /* just ignore the advice */
|
|
|
|
if (vma->anon_vma) {
|
|
err = unmerge_ksm_pages(vma, start, end);
|
|
if (err)
|
|
return err;
|
|
}
|
|
|
|
*vm_flags &= ~VM_MERGEABLE;
|
|
break;
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
int __ksm_enter(struct mm_struct *mm)
|
|
{
|
|
struct mm_slot *mm_slot;
|
|
int needs_wakeup;
|
|
|
|
mm_slot = alloc_mm_slot();
|
|
if (!mm_slot)
|
|
return -ENOMEM;
|
|
|
|
/* Check ksm_run too? Would need tighter locking */
|
|
needs_wakeup = list_empty(&ksm_mm_head.mm_list);
|
|
|
|
spin_lock(&ksm_mmlist_lock);
|
|
insert_to_mm_slots_hash(mm, mm_slot);
|
|
/*
|
|
* When KSM_RUN_MERGE (or KSM_RUN_STOP),
|
|
* insert just behind the scanning cursor, to let the area settle
|
|
* down a little; when fork is followed by immediate exec, we don't
|
|
* want ksmd to waste time setting up and tearing down an rmap_list.
|
|
*
|
|
* But when KSM_RUN_UNMERGE, it's important to insert ahead of its
|
|
* scanning cursor, otherwise KSM pages in newly forked mms will be
|
|
* missed: then we might as well insert at the end of the list.
|
|
*/
|
|
if (ksm_run & KSM_RUN_UNMERGE)
|
|
list_add_tail(&mm_slot->mm_list, &ksm_mm_head.mm_list);
|
|
else
|
|
list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
|
|
set_bit(MMF_VM_MERGEABLE, &mm->flags);
|
|
mmgrab(mm);
|
|
|
|
if (needs_wakeup)
|
|
wake_up_interruptible(&ksm_thread_wait);
|
|
|
|
return 0;
|
|
}
|
|
|
|
void __ksm_exit(struct mm_struct *mm)
|
|
{
|
|
struct mm_slot *mm_slot;
|
|
int easy_to_free = 0;
|
|
|
|
/*
|
|
* This process is exiting: if it's straightforward (as is the
|
|
* case when ksmd was never running), free mm_slot immediately.
|
|
* But if it's at the cursor or has rmap_items linked to it, use
|
|
* mmap_sem to synchronize with any break_cows before pagetables
|
|
* are freed, and leave the mm_slot on the list for ksmd to free.
|
|
* Beware: ksm may already have noticed it exiting and freed the slot.
|
|
*/
|
|
|
|
spin_lock(&ksm_mmlist_lock);
|
|
mm_slot = get_mm_slot(mm);
|
|
if (mm_slot && ksm_scan.mm_slot != mm_slot) {
|
|
if (!mm_slot->rmap_list) {
|
|
hash_del(&mm_slot->link);
|
|
list_del(&mm_slot->mm_list);
|
|
easy_to_free = 1;
|
|
} else {
|
|
list_move(&mm_slot->mm_list,
|
|
&ksm_scan.mm_slot->mm_list);
|
|
}
|
|
}
|
|
spin_unlock(&ksm_mmlist_lock);
|
|
|
|
if (easy_to_free) {
|
|
free_mm_slot(mm_slot);
|
|
clear_bit(MMF_VM_MERGEABLE, &mm->flags);
|
|
mmdrop(mm);
|
|
} else if (mm_slot) {
|
|
down_write(&mm->mmap_sem);
|
|
up_write(&mm->mmap_sem);
|
|
}
|
|
}
|
|
|
|
struct page *ksm_might_need_to_copy(struct page *page,
|
|
struct vm_area_struct *vma, unsigned long address)
|
|
{
|
|
struct anon_vma *anon_vma = page_anon_vma(page);
|
|
struct page *new_page;
|
|
|
|
if (PageKsm(page)) {
|
|
if (page_stable_node(page) &&
|
|
!(ksm_run & KSM_RUN_UNMERGE))
|
|
return page; /* no need to copy it */
|
|
} else if (!anon_vma) {
|
|
return page; /* no need to copy it */
|
|
} else if (anon_vma->root == vma->anon_vma->root &&
|
|
page->index == linear_page_index(vma, address)) {
|
|
return page; /* still no need to copy it */
|
|
}
|
|
if (!PageUptodate(page))
|
|
return page; /* let do_swap_page report the error */
|
|
|
|
new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
|
|
if (new_page) {
|
|
copy_user_highpage(new_page, page, address, vma);
|
|
|
|
SetPageDirty(new_page);
|
|
__SetPageUptodate(new_page);
|
|
__SetPageLocked(new_page);
|
|
}
|
|
|
|
return new_page;
|
|
}
|
|
|
|
void rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc)
|
|
{
|
|
struct stable_node *stable_node;
|
|
struct rmap_item *rmap_item;
|
|
int search_new_forks = 0;
|
|
|
|
VM_BUG_ON_PAGE(!PageKsm(page), page);
|
|
|
|
/*
|
|
* Rely on the page lock to protect against concurrent modifications
|
|
* to that page's node of the stable tree.
|
|
*/
|
|
VM_BUG_ON_PAGE(!PageLocked(page), page);
|
|
|
|
stable_node = page_stable_node(page);
|
|
if (!stable_node)
|
|
return;
|
|
again:
|
|
hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
|
|
struct anon_vma *anon_vma = rmap_item->anon_vma;
|
|
struct anon_vma_chain *vmac;
|
|
struct vm_area_struct *vma;
|
|
|
|
cond_resched();
|
|
anon_vma_lock_read(anon_vma);
|
|
anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
|
|
0, ULONG_MAX) {
|
|
cond_resched();
|
|
vma = vmac->vma;
|
|
if (rmap_item->address < vma->vm_start ||
|
|
rmap_item->address >= vma->vm_end)
|
|
continue;
|
|
/*
|
|
* Initially we examine only the vma which covers this
|
|
* rmap_item; but later, if there is still work to do,
|
|
* we examine covering vmas in other mms: in case they
|
|
* were forked from the original since ksmd passed.
|
|
*/
|
|
if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
|
|
continue;
|
|
|
|
if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
|
|
continue;
|
|
|
|
if (!rwc->rmap_one(page, vma,
|
|
rmap_item->address, rwc->arg)) {
|
|
anon_vma_unlock_read(anon_vma);
|
|
return;
|
|
}
|
|
if (rwc->done && rwc->done(page)) {
|
|
anon_vma_unlock_read(anon_vma);
|
|
return;
|
|
}
|
|
}
|
|
anon_vma_unlock_read(anon_vma);
|
|
}
|
|
if (!search_new_forks++)
|
|
goto again;
|
|
}
|
|
|
|
#ifdef CONFIG_MIGRATION
|
|
void ksm_migrate_page(struct page *newpage, struct page *oldpage)
|
|
{
|
|
struct stable_node *stable_node;
|
|
|
|
VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage);
|
|
VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
|
|
VM_BUG_ON_PAGE(newpage->mapping != oldpage->mapping, newpage);
|
|
|
|
stable_node = page_stable_node(newpage);
|
|
if (stable_node) {
|
|
VM_BUG_ON_PAGE(stable_node->kpfn != page_to_pfn(oldpage), oldpage);
|
|
stable_node->kpfn = page_to_pfn(newpage);
|
|
/*
|
|
* newpage->mapping was set in advance; now we need smp_wmb()
|
|
* to make sure that the new stable_node->kpfn is visible
|
|
* to get_ksm_page() before it can see that oldpage->mapping
|
|
* has gone stale (or that PageSwapCache has been cleared).
|
|
*/
|
|
smp_wmb();
|
|
set_page_stable_node(oldpage, NULL);
|
|
}
|
|
}
|
|
#endif /* CONFIG_MIGRATION */
|
|
|
|
#ifdef CONFIG_MEMORY_HOTREMOVE
|
|
static void wait_while_offlining(void)
|
|
{
|
|
while (ksm_run & KSM_RUN_OFFLINE) {
|
|
mutex_unlock(&ksm_thread_mutex);
|
|
wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
|
|
TASK_UNINTERRUPTIBLE);
|
|
mutex_lock(&ksm_thread_mutex);
|
|
}
|
|
}
|
|
|
|
static bool stable_node_dup_remove_range(struct stable_node *stable_node,
|
|
unsigned long start_pfn,
|
|
unsigned long end_pfn)
|
|
{
|
|
if (stable_node->kpfn >= start_pfn &&
|
|
stable_node->kpfn < end_pfn) {
|
|
/*
|
|
* Don't get_ksm_page, page has already gone:
|
|
* which is why we keep kpfn instead of page*
|
|
*/
|
|
remove_node_from_stable_tree(stable_node);
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
static bool stable_node_chain_remove_range(struct stable_node *stable_node,
|
|
unsigned long start_pfn,
|
|
unsigned long end_pfn,
|
|
struct rb_root *root)
|
|
{
|
|
struct stable_node *dup;
|
|
struct hlist_node *hlist_safe;
|
|
|
|
if (!is_stable_node_chain(stable_node)) {
|
|
VM_BUG_ON(is_stable_node_dup(stable_node));
|
|
return stable_node_dup_remove_range(stable_node, start_pfn,
|
|
end_pfn);
|
|
}
|
|
|
|
hlist_for_each_entry_safe(dup, hlist_safe,
|
|
&stable_node->hlist, hlist_dup) {
|
|
VM_BUG_ON(!is_stable_node_dup(dup));
|
|
stable_node_dup_remove_range(dup, start_pfn, end_pfn);
|
|
}
|
|
if (hlist_empty(&stable_node->hlist)) {
|
|
free_stable_node_chain(stable_node, root);
|
|
return true; /* notify caller that tree was rebalanced */
|
|
} else
|
|
return false;
|
|
}
|
|
|
|
static void ksm_check_stable_tree(unsigned long start_pfn,
|
|
unsigned long end_pfn)
|
|
{
|
|
struct stable_node *stable_node, *next;
|
|
struct rb_node *node;
|
|
int nid;
|
|
|
|
for (nid = 0; nid < ksm_nr_node_ids; nid++) {
|
|
node = rb_first(root_stable_tree + nid);
|
|
while (node) {
|
|
stable_node = rb_entry(node, struct stable_node, node);
|
|
if (stable_node_chain_remove_range(stable_node,
|
|
start_pfn, end_pfn,
|
|
root_stable_tree +
|
|
nid))
|
|
node = rb_first(root_stable_tree + nid);
|
|
else
|
|
node = rb_next(node);
|
|
cond_resched();
|
|
}
|
|
}
|
|
list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
|
|
if (stable_node->kpfn >= start_pfn &&
|
|
stable_node->kpfn < end_pfn)
|
|
remove_node_from_stable_tree(stable_node);
|
|
cond_resched();
|
|
}
|
|
}
|
|
|
|
static int ksm_memory_callback(struct notifier_block *self,
|
|
unsigned long action, void *arg)
|
|
{
|
|
struct memory_notify *mn = arg;
|
|
|
|
switch (action) {
|
|
case MEM_GOING_OFFLINE:
|
|
/*
|
|
* Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
|
|
* and remove_all_stable_nodes() while memory is going offline:
|
|
* it is unsafe for them to touch the stable tree at this time.
|
|
* But unmerge_ksm_pages(), rmap lookups and other entry points
|
|
* which do not need the ksm_thread_mutex are all safe.
|
|
*/
|
|
mutex_lock(&ksm_thread_mutex);
|
|
ksm_run |= KSM_RUN_OFFLINE;
|
|
mutex_unlock(&ksm_thread_mutex);
|
|
break;
|
|
|
|
case MEM_OFFLINE:
|
|
/*
|
|
* Most of the work is done by page migration; but there might
|
|
* be a few stable_nodes left over, still pointing to struct
|
|
* pages which have been offlined: prune those from the tree,
|
|
* otherwise get_ksm_page() might later try to access a
|
|
* non-existent struct page.
|
|
*/
|
|
ksm_check_stable_tree(mn->start_pfn,
|
|
mn->start_pfn + mn->nr_pages);
|
|
/* fallthrough */
|
|
|
|
case MEM_CANCEL_OFFLINE:
|
|
mutex_lock(&ksm_thread_mutex);
|
|
ksm_run &= ~KSM_RUN_OFFLINE;
|
|
mutex_unlock(&ksm_thread_mutex);
|
|
|
|
smp_mb(); /* wake_up_bit advises this */
|
|
wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
|
|
break;
|
|
}
|
|
return NOTIFY_OK;
|
|
}
|
|
#else
|
|
static void wait_while_offlining(void)
|
|
{
|
|
}
|
|
#endif /* CONFIG_MEMORY_HOTREMOVE */
|
|
|
|
#ifdef CONFIG_SYSFS
|
|
/*
|
|
* This all compiles without CONFIG_SYSFS, but is a waste of space.
|
|
*/
|
|
|
|
#define KSM_ATTR_RO(_name) \
|
|
static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
|
|
#define KSM_ATTR(_name) \
|
|
static struct kobj_attribute _name##_attr = \
|
|
__ATTR(_name, 0644, _name##_show, _name##_store)
|
|
|
|
static ssize_t sleep_millisecs_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
|
|
}
|
|
|
|
static ssize_t sleep_millisecs_store(struct kobject *kobj,
|
|
struct kobj_attribute *attr,
|
|
const char *buf, size_t count)
|
|
{
|
|
unsigned long msecs;
|
|
int err;
|
|
|
|
err = kstrtoul(buf, 10, &msecs);
|
|
if (err || msecs > UINT_MAX)
|
|
return -EINVAL;
|
|
|
|
ksm_thread_sleep_millisecs = msecs;
|
|
|
|
return count;
|
|
}
|
|
KSM_ATTR(sleep_millisecs);
|
|
|
|
static ssize_t pages_to_scan_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
|
|
}
|
|
|
|
static ssize_t pages_to_scan_store(struct kobject *kobj,
|
|
struct kobj_attribute *attr,
|
|
const char *buf, size_t count)
|
|
{
|
|
int err;
|
|
unsigned long nr_pages;
|
|
|
|
err = kstrtoul(buf, 10, &nr_pages);
|
|
if (err || nr_pages > UINT_MAX)
|
|
return -EINVAL;
|
|
|
|
ksm_thread_pages_to_scan = nr_pages;
|
|
|
|
return count;
|
|
}
|
|
KSM_ATTR(pages_to_scan);
|
|
|
|
static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
|
|
char *buf)
|
|
{
|
|
return sprintf(buf, "%lu\n", ksm_run);
|
|
}
|
|
|
|
static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
|
|
const char *buf, size_t count)
|
|
{
|
|
int err;
|
|
unsigned long flags;
|
|
|
|
err = kstrtoul(buf, 10, &flags);
|
|
if (err || flags > UINT_MAX)
|
|
return -EINVAL;
|
|
if (flags > KSM_RUN_UNMERGE)
|
|
return -EINVAL;
|
|
|
|
/*
|
|
* KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
|
|
* KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
|
|
* breaking COW to free the pages_shared (but leaves mm_slots
|
|
* on the list for when ksmd may be set running again).
|
|
*/
|
|
|
|
mutex_lock(&ksm_thread_mutex);
|
|
wait_while_offlining();
|
|
if (ksm_run != flags) {
|
|
ksm_run = flags;
|
|
if (flags & KSM_RUN_UNMERGE) {
|
|
set_current_oom_origin();
|
|
err = unmerge_and_remove_all_rmap_items();
|
|
clear_current_oom_origin();
|
|
if (err) {
|
|
ksm_run = KSM_RUN_STOP;
|
|
count = err;
|
|
}
|
|
}
|
|
}
|
|
mutex_unlock(&ksm_thread_mutex);
|
|
|
|
if (flags & KSM_RUN_MERGE)
|
|
wake_up_interruptible(&ksm_thread_wait);
|
|
|
|
return count;
|
|
}
|
|
KSM_ATTR(run);
|
|
|
|
#ifdef CONFIG_NUMA
|
|
static ssize_t merge_across_nodes_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
return sprintf(buf, "%u\n", ksm_merge_across_nodes);
|
|
}
|
|
|
|
static ssize_t merge_across_nodes_store(struct kobject *kobj,
|
|
struct kobj_attribute *attr,
|
|
const char *buf, size_t count)
|
|
{
|
|
int err;
|
|
unsigned long knob;
|
|
|
|
err = kstrtoul(buf, 10, &knob);
|
|
if (err)
|
|
return err;
|
|
if (knob > 1)
|
|
return -EINVAL;
|
|
|
|
mutex_lock(&ksm_thread_mutex);
|
|
wait_while_offlining();
|
|
if (ksm_merge_across_nodes != knob) {
|
|
if (ksm_pages_shared || remove_all_stable_nodes())
|
|
err = -EBUSY;
|
|
else if (root_stable_tree == one_stable_tree) {
|
|
struct rb_root *buf;
|
|
/*
|
|
* This is the first time that we switch away from the
|
|
* default of merging across nodes: must now allocate
|
|
* a buffer to hold as many roots as may be needed.
|
|
* Allocate stable and unstable together:
|
|
* MAXSMP NODES_SHIFT 10 will use 16kB.
|
|
*/
|
|
buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf),
|
|
GFP_KERNEL);
|
|
/* Let us assume that RB_ROOT is NULL is zero */
|
|
if (!buf)
|
|
err = -ENOMEM;
|
|
else {
|
|
root_stable_tree = buf;
|
|
root_unstable_tree = buf + nr_node_ids;
|
|
/* Stable tree is empty but not the unstable */
|
|
root_unstable_tree[0] = one_unstable_tree[0];
|
|
}
|
|
}
|
|
if (!err) {
|
|
ksm_merge_across_nodes = knob;
|
|
ksm_nr_node_ids = knob ? 1 : nr_node_ids;
|
|
}
|
|
}
|
|
mutex_unlock(&ksm_thread_mutex);
|
|
|
|
return err ? err : count;
|
|
}
|
|
KSM_ATTR(merge_across_nodes);
|
|
#endif
|
|
|
|
static ssize_t use_zero_pages_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
return sprintf(buf, "%u\n", ksm_use_zero_pages);
|
|
}
|
|
static ssize_t use_zero_pages_store(struct kobject *kobj,
|
|
struct kobj_attribute *attr,
|
|
const char *buf, size_t count)
|
|
{
|
|
int err;
|
|
bool value;
|
|
|
|
err = kstrtobool(buf, &value);
|
|
if (err)
|
|
return -EINVAL;
|
|
|
|
ksm_use_zero_pages = value;
|
|
|
|
return count;
|
|
}
|
|
KSM_ATTR(use_zero_pages);
|
|
|
|
static ssize_t max_page_sharing_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
return sprintf(buf, "%u\n", ksm_max_page_sharing);
|
|
}
|
|
|
|
static ssize_t max_page_sharing_store(struct kobject *kobj,
|
|
struct kobj_attribute *attr,
|
|
const char *buf, size_t count)
|
|
{
|
|
int err;
|
|
int knob;
|
|
|
|
err = kstrtoint(buf, 10, &knob);
|
|
if (err)
|
|
return err;
|
|
/*
|
|
* When a KSM page is created it is shared by 2 mappings. This
|
|
* being a signed comparison, it implicitly verifies it's not
|
|
* negative.
|
|
*/
|
|
if (knob < 2)
|
|
return -EINVAL;
|
|
|
|
if (READ_ONCE(ksm_max_page_sharing) == knob)
|
|
return count;
|
|
|
|
mutex_lock(&ksm_thread_mutex);
|
|
wait_while_offlining();
|
|
if (ksm_max_page_sharing != knob) {
|
|
if (ksm_pages_shared || remove_all_stable_nodes())
|
|
err = -EBUSY;
|
|
else
|
|
ksm_max_page_sharing = knob;
|
|
}
|
|
mutex_unlock(&ksm_thread_mutex);
|
|
|
|
return err ? err : count;
|
|
}
|
|
KSM_ATTR(max_page_sharing);
|
|
|
|
static ssize_t pages_shared_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
return sprintf(buf, "%lu\n", ksm_pages_shared);
|
|
}
|
|
KSM_ATTR_RO(pages_shared);
|
|
|
|
static ssize_t pages_sharing_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
return sprintf(buf, "%lu\n", ksm_pages_sharing);
|
|
}
|
|
KSM_ATTR_RO(pages_sharing);
|
|
|
|
static ssize_t pages_unshared_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
return sprintf(buf, "%lu\n", ksm_pages_unshared);
|
|
}
|
|
KSM_ATTR_RO(pages_unshared);
|
|
|
|
static ssize_t pages_volatile_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
long ksm_pages_volatile;
|
|
|
|
ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
|
|
- ksm_pages_sharing - ksm_pages_unshared;
|
|
/*
|
|
* It was not worth any locking to calculate that statistic,
|
|
* but it might therefore sometimes be negative: conceal that.
|
|
*/
|
|
if (ksm_pages_volatile < 0)
|
|
ksm_pages_volatile = 0;
|
|
return sprintf(buf, "%ld\n", ksm_pages_volatile);
|
|
}
|
|
KSM_ATTR_RO(pages_volatile);
|
|
|
|
static ssize_t stable_node_dups_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
return sprintf(buf, "%lu\n", ksm_stable_node_dups);
|
|
}
|
|
KSM_ATTR_RO(stable_node_dups);
|
|
|
|
static ssize_t stable_node_chains_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
return sprintf(buf, "%lu\n", ksm_stable_node_chains);
|
|
}
|
|
KSM_ATTR_RO(stable_node_chains);
|
|
|
|
static ssize_t
|
|
stable_node_chains_prune_millisecs_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr,
|
|
char *buf)
|
|
{
|
|
return sprintf(buf, "%u\n", ksm_stable_node_chains_prune_millisecs);
|
|
}
|
|
|
|
static ssize_t
|
|
stable_node_chains_prune_millisecs_store(struct kobject *kobj,
|
|
struct kobj_attribute *attr,
|
|
const char *buf, size_t count)
|
|
{
|
|
unsigned long msecs;
|
|
int err;
|
|
|
|
err = kstrtoul(buf, 10, &msecs);
|
|
if (err || msecs > UINT_MAX)
|
|
return -EINVAL;
|
|
|
|
ksm_stable_node_chains_prune_millisecs = msecs;
|
|
|
|
return count;
|
|
}
|
|
KSM_ATTR(stable_node_chains_prune_millisecs);
|
|
|
|
static ssize_t full_scans_show(struct kobject *kobj,
|
|
struct kobj_attribute *attr, char *buf)
|
|
{
|
|
return sprintf(buf, "%lu\n", ksm_scan.seqnr);
|
|
}
|
|
KSM_ATTR_RO(full_scans);
|
|
|
|
static struct attribute *ksm_attrs[] = {
|
|
&sleep_millisecs_attr.attr,
|
|
&pages_to_scan_attr.attr,
|
|
&run_attr.attr,
|
|
&pages_shared_attr.attr,
|
|
&pages_sharing_attr.attr,
|
|
&pages_unshared_attr.attr,
|
|
&pages_volatile_attr.attr,
|
|
&full_scans_attr.attr,
|
|
#ifdef CONFIG_NUMA
|
|
&merge_across_nodes_attr.attr,
|
|
#endif
|
|
&max_page_sharing_attr.attr,
|
|
&stable_node_chains_attr.attr,
|
|
&stable_node_dups_attr.attr,
|
|
&stable_node_chains_prune_millisecs_attr.attr,
|
|
&use_zero_pages_attr.attr,
|
|
NULL,
|
|
};
|
|
|
|
static const struct attribute_group ksm_attr_group = {
|
|
.attrs = ksm_attrs,
|
|
.name = "ksm",
|
|
};
|
|
#endif /* CONFIG_SYSFS */
|
|
|
|
static int __init ksm_init(void)
|
|
{
|
|
struct task_struct *ksm_thread;
|
|
int err;
|
|
|
|
/* The correct value depends on page size and endianness */
|
|
zero_checksum = calc_checksum(ZERO_PAGE(0));
|
|
/* Default to false for backwards compatibility */
|
|
ksm_use_zero_pages = false;
|
|
|
|
err = ksm_slab_init();
|
|
if (err)
|
|
goto out;
|
|
|
|
ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
|
|
if (IS_ERR(ksm_thread)) {
|
|
pr_err("ksm: creating kthread failed\n");
|
|
err = PTR_ERR(ksm_thread);
|
|
goto out_free;
|
|
}
|
|
|
|
#ifdef CONFIG_SYSFS
|
|
err = sysfs_create_group(mm_kobj, &ksm_attr_group);
|
|
if (err) {
|
|
pr_err("ksm: register sysfs failed\n");
|
|
kthread_stop(ksm_thread);
|
|
goto out_free;
|
|
}
|
|
#else
|
|
ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
|
|
|
|
#endif /* CONFIG_SYSFS */
|
|
|
|
#ifdef CONFIG_MEMORY_HOTREMOVE
|
|
/* There is no significance to this priority 100 */
|
|
hotplug_memory_notifier(ksm_memory_callback, 100);
|
|
#endif
|
|
return 0;
|
|
|
|
out_free:
|
|
ksm_slab_free();
|
|
out:
|
|
return err;
|
|
}
|
|
subsys_initcall(ksm_init);
|