426 lines
14 KiB
C
426 lines
14 KiB
C
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Memory allocator, based on tcmalloc.
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// http://goog-perftools.sourceforge.net/doc/tcmalloc.html
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// The main allocator works in runs of pages.
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// Small allocation sizes (up to and including 32 kB) are
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// rounded to one of about 100 size classes, each of which
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// has its own free list of objects of exactly that size.
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// Any free page of memory can be split into a set of objects
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// of one size class, which are then managed using free list
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// allocators.
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//
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// The allocator's data structures are:
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//
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// FixAlloc: a free-list allocator for fixed-size objects,
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// used to manage storage used by the allocator.
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// MHeap: the malloc heap, managed at page (4096-byte) granularity.
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// MSpan: a run of pages managed by the MHeap.
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// MCentral: a shared free list for a given size class.
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// MCache: a per-thread (in Go, per-M) cache for small objects.
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// MStats: allocation statistics.
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//
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// Allocating a small object proceeds up a hierarchy of caches:
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//
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// 1. Round the size up to one of the small size classes
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// and look in the corresponding MCache free list.
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// If the list is not empty, allocate an object from it.
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// This can all be done without acquiring a lock.
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//
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// 2. If the MCache free list is empty, replenish it by
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// taking a bunch of objects from the MCentral free list.
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// Moving a bunch amortizes the cost of acquiring the MCentral lock.
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//
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// 3. If the MCentral free list is empty, replenish it by
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// allocating a run of pages from the MHeap and then
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// chopping that memory into a objects of the given size.
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// Allocating many objects amortizes the cost of locking
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// the heap.
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//
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// 4. If the MHeap is empty or has no page runs large enough,
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// allocate a new group of pages (at least 1MB) from the
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// operating system. Allocating a large run of pages
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// amortizes the cost of talking to the operating system.
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//
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// Freeing a small object proceeds up the same hierarchy:
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//
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// 1. Look up the size class for the object and add it to
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// the MCache free list.
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//
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// 2. If the MCache free list is too long or the MCache has
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// too much memory, return some to the MCentral free lists.
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//
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// 3. If all the objects in a given span have returned to
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// the MCentral list, return that span to the page heap.
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//
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// 4. If the heap has too much memory, return some to the
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// operating system.
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//
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// TODO(rsc): Step 4 is not implemented.
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//
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// Allocating and freeing a large object uses the page heap
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// directly, bypassing the MCache and MCentral free lists.
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//
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// The small objects on the MCache and MCentral free lists
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// may or may not be zeroed. They are zeroed if and only if
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// the second word of the object is zero. The spans in the
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// page heap are always zeroed. When a span full of objects
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// is returned to the page heap, the objects that need to be
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// are zeroed first. There are two main benefits to delaying the
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// zeroing this way:
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//
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// 1. stack frames allocated from the small object lists
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// can avoid zeroing altogether.
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// 2. the cost of zeroing when reusing a small object is
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// charged to the mutator, not the garbage collector.
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//
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// This C code was written with an eye toward translating to Go
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// in the future. Methods have the form Type_Method(Type *t, ...).
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typedef struct MCentral MCentral;
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typedef struct MHeap MHeap;
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typedef struct MSpan MSpan;
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typedef struct MStats MStats;
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typedef struct MLink MLink;
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enum
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{
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PageShift = 12,
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PageSize = 1<<PageShift,
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PageMask = PageSize - 1,
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};
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typedef uintptr PageID; // address >> PageShift
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enum
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{
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// Computed constant. The definition of MaxSmallSize and the
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// algorithm in msize.c produce some number of different allocation
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// size classes. NumSizeClasses is that number. It's needed here
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// because there are static arrays of this length; when msize runs its
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// size choosing algorithm it double-checks that NumSizeClasses agrees.
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NumSizeClasses = 61,
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// Tunable constants.
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MaxSmallSize = 32<<10,
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FixAllocChunk = 128<<10, // Chunk size for FixAlloc
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MaxMCacheListLen = 256, // Maximum objects on MCacheList
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MaxMCacheSize = 2<<20, // Maximum bytes in one MCache
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MaxMHeapList = 1<<(20 - PageShift), // Maximum page length for fixed-size list in MHeap.
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HeapAllocChunk = 1<<20, // Chunk size for heap growth
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// Number of bits in page to span calculations (4k pages).
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// On 64-bit, we limit the arena to 16G, so 22 bits suffices.
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// On 32-bit, we don't bother limiting anything: 20 bits for 4G.
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#if __SIZEOF_POINTER__ == 8
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MHeapMap_Bits = 22,
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#else
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MHeapMap_Bits = 20,
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#endif
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// Max number of threads to run garbage collection.
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// 2, 3, and 4 are all plausible maximums depending
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// on the hardware details of the machine. The second
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// proc is the one that helps the most (after the first),
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// so start with just 2 for now.
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MaxGcproc = 2,
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};
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// A generic linked list of blocks. (Typically the block is bigger than sizeof(MLink).)
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struct MLink
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{
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MLink *next;
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};
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// SysAlloc obtains a large chunk of zeroed memory from the
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// operating system, typically on the order of a hundred kilobytes
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// or a megabyte. If the pointer argument is non-nil, the caller
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// wants a mapping there or nowhere.
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//
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// SysUnused notifies the operating system that the contents
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// of the memory region are no longer needed and can be reused
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// for other purposes. The program reserves the right to start
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// accessing those pages in the future.
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//
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// SysFree returns it unconditionally; this is only used if
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// an out-of-memory error has been detected midway through
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// an allocation. It is okay if SysFree is a no-op.
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//
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// SysReserve reserves address space without allocating memory.
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// If the pointer passed to it is non-nil, the caller wants the
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// reservation there, but SysReserve can still choose another
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// location if that one is unavailable.
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//
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// SysMap maps previously reserved address space for use.
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void* runtime_SysAlloc(uintptr nbytes);
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void runtime_SysFree(void *v, uintptr nbytes);
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void runtime_SysUnused(void *v, uintptr nbytes);
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void runtime_SysMap(void *v, uintptr nbytes);
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void* runtime_SysReserve(void *v, uintptr nbytes);
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// FixAlloc is a simple free-list allocator for fixed size objects.
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// Malloc uses a FixAlloc wrapped around SysAlloc to manages its
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// MCache and MSpan objects.
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//
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// Memory returned by FixAlloc_Alloc is not zeroed.
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// The caller is responsible for locking around FixAlloc calls.
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// Callers can keep state in the object but the first word is
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// smashed by freeing and reallocating.
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struct FixAlloc
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{
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uintptr size;
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void *(*alloc)(uintptr);
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void (*first)(void *arg, byte *p); // called first time p is returned
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void *arg;
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MLink *list;
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byte *chunk;
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uint32 nchunk;
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uintptr inuse; // in-use bytes now
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uintptr sys; // bytes obtained from system
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};
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void runtime_FixAlloc_Init(FixAlloc *f, uintptr size, void *(*alloc)(uintptr), void (*first)(void*, byte*), void *arg);
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void* runtime_FixAlloc_Alloc(FixAlloc *f);
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void runtime_FixAlloc_Free(FixAlloc *f, void *p);
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// Statistics.
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// Shared with Go: if you edit this structure, also edit extern.go.
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struct MStats
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{
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// General statistics.
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uint64 alloc; // bytes allocated and still in use
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uint64 total_alloc; // bytes allocated (even if freed)
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uint64 sys; // bytes obtained from system (should be sum of xxx_sys below, no locking, approximate)
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uint64 nlookup; // number of pointer lookups
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uint64 nmalloc; // number of mallocs
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uint64 nfree; // number of frees
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// Statistics about malloc heap.
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// protected by mheap.Lock
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uint64 heap_alloc; // bytes allocated and still in use
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uint64 heap_sys; // bytes obtained from system
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uint64 heap_idle; // bytes in idle spans
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uint64 heap_inuse; // bytes in non-idle spans
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uint64 heap_objects; // total number of allocated objects
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// Statistics about allocation of low-level fixed-size structures.
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// Protected by FixAlloc locks.
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uint64 stacks_inuse; // bootstrap stacks
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uint64 stacks_sys;
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uint64 mspan_inuse; // MSpan structures
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uint64 mspan_sys;
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uint64 mcache_inuse; // MCache structures
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uint64 mcache_sys;
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uint64 buckhash_sys; // profiling bucket hash table
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// Statistics about garbage collector.
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// Protected by stopping the world during GC.
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uint64 next_gc; // next GC (in heap_alloc time)
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uint64 pause_total_ns;
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uint64 pause_ns[256];
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uint32 numgc;
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bool enablegc;
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bool debuggc;
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// Statistics about allocation size classes.
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struct {
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uint32 size;
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uint64 nmalloc;
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uint64 nfree;
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} by_size[NumSizeClasses];
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};
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extern MStats mstats
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__asm__ ("libgo_runtime.runtime.MemStats");
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// Size classes. Computed and initialized by InitSizes.
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//
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// SizeToClass(0 <= n <= MaxSmallSize) returns the size class,
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// 1 <= sizeclass < NumSizeClasses, for n.
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// Size class 0 is reserved to mean "not small".
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//
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// class_to_size[i] = largest size in class i
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// class_to_allocnpages[i] = number of pages to allocate when
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// making new objects in class i
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// class_to_transfercount[i] = number of objects to move when
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// taking a bunch of objects out of the central lists
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// and putting them in the thread free list.
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int32 runtime_SizeToClass(int32);
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extern int32 runtime_class_to_size[NumSizeClasses];
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extern int32 runtime_class_to_allocnpages[NumSizeClasses];
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extern int32 runtime_class_to_transfercount[NumSizeClasses];
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extern void runtime_InitSizes(void);
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// Per-thread (in Go, per-M) cache for small objects.
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// No locking needed because it is per-thread (per-M).
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typedef struct MCacheList MCacheList;
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struct MCacheList
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{
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MLink *list;
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uint32 nlist;
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uint32 nlistmin;
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};
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struct MCache
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{
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MCacheList list[NumSizeClasses];
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uint64 size;
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int64 local_cachealloc; // bytes allocated (or freed) from cache since last lock of heap
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int64 local_objects; // objects allocated (or freed) from cache since last lock of heap
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int64 local_alloc; // bytes allocated (or freed) since last lock of heap
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int64 local_total_alloc; // bytes allocated (even if freed) since last lock of heap
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int64 local_nmalloc; // number of mallocs since last lock of heap
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int64 local_nfree; // number of frees since last lock of heap
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int64 local_nlookup; // number of pointer lookups since last lock of heap
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int32 next_sample; // trigger heap sample after allocating this many bytes
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// Statistics about allocation size classes since last lock of heap
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struct {
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int64 nmalloc;
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int64 nfree;
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} local_by_size[NumSizeClasses];
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};
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void* runtime_MCache_Alloc(MCache *c, int32 sizeclass, uintptr size, int32 zeroed);
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void runtime_MCache_Free(MCache *c, void *p, int32 sizeclass, uintptr size);
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void runtime_MCache_ReleaseAll(MCache *c);
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// An MSpan is a run of pages.
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enum
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{
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MSpanInUse = 0,
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MSpanFree,
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MSpanListHead,
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MSpanDead,
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};
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struct MSpan
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{
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MSpan *next; // in a span linked list
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MSpan *prev; // in a span linked list
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MSpan *allnext; // in the list of all spans
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PageID start; // starting page number
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uintptr npages; // number of pages in span
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MLink *freelist; // list of free objects
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uint32 ref; // number of allocated objects in this span
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uint32 sizeclass; // size class
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uint32 state; // MSpanInUse etc
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byte *limit; // end of data in span
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};
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void runtime_MSpan_Init(MSpan *span, PageID start, uintptr npages);
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// Every MSpan is in one doubly-linked list,
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// either one of the MHeap's free lists or one of the
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// MCentral's span lists. We use empty MSpan structures as list heads.
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void runtime_MSpanList_Init(MSpan *list);
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bool runtime_MSpanList_IsEmpty(MSpan *list);
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void runtime_MSpanList_Insert(MSpan *list, MSpan *span);
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void runtime_MSpanList_Remove(MSpan *span); // from whatever list it is in
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// Central list of free objects of a given size.
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struct MCentral
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{
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Lock;
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int32 sizeclass;
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MSpan nonempty;
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MSpan empty;
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int32 nfree;
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};
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void runtime_MCentral_Init(MCentral *c, int32 sizeclass);
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int32 runtime_MCentral_AllocList(MCentral *c, int32 n, MLink **first);
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void runtime_MCentral_FreeList(MCentral *c, int32 n, MLink *first);
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// Main malloc heap.
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// The heap itself is the "free[]" and "large" arrays,
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// but all the other global data is here too.
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struct MHeap
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{
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Lock;
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MSpan free[MaxMHeapList]; // free lists of given length
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MSpan large; // free lists length >= MaxMHeapList
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MSpan *allspans;
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// span lookup
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MSpan *map[1<<MHeapMap_Bits];
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// range of addresses we might see in the heap
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byte *bitmap;
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uintptr bitmap_mapped;
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byte *arena_start;
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byte *arena_used;
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byte *arena_end;
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// central free lists for small size classes.
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// the union makes sure that the MCentrals are
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// spaced CacheLineSize bytes apart, so that each MCentral.Lock
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// gets its own cache line.
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union {
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MCentral;
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byte pad[CacheLineSize];
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} central[NumSizeClasses];
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FixAlloc spanalloc; // allocator for Span*
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FixAlloc cachealloc; // allocator for MCache*
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};
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extern MHeap runtime_mheap;
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void runtime_MHeap_Init(MHeap *h, void *(*allocator)(uintptr));
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MSpan* runtime_MHeap_Alloc(MHeap *h, uintptr npage, int32 sizeclass, int32 acct);
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void runtime_MHeap_Free(MHeap *h, MSpan *s, int32 acct);
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MSpan* runtime_MHeap_Lookup(MHeap *h, void *v);
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MSpan* runtime_MHeap_LookupMaybe(MHeap *h, void *v);
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void runtime_MGetSizeClassInfo(int32 sizeclass, uintptr *size, int32 *npages, int32 *nobj);
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void* runtime_MHeap_SysAlloc(MHeap *h, uintptr n);
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void runtime_MHeap_MapBits(MHeap *h);
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void* runtime_mallocgc(uintptr size, uint32 flag, int32 dogc, int32 zeroed);
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int32 runtime_mlookup(void *v, byte **base, uintptr *size, MSpan **s);
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void runtime_gc(int32 force);
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void runtime_markallocated(void *v, uintptr n, bool noptr);
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void runtime_checkallocated(void *v, uintptr n);
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void runtime_markfreed(void *v, uintptr n);
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void runtime_checkfreed(void *v, uintptr n);
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int32 runtime_checking;
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void runtime_markspan(void *v, uintptr size, uintptr n, bool leftover);
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void runtime_unmarkspan(void *v, uintptr size);
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bool runtime_blockspecial(void*);
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void runtime_setblockspecial(void*, bool);
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void runtime_purgecachedstats(M*);
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enum
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{
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// flags to malloc
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FlagNoPointers = 1<<0, // no pointers here
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FlagNoProfiling = 1<<1, // must not profile
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FlagNoGC = 1<<2, // must not free or scan for pointers
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};
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void runtime_MProf_Malloc(void*, uintptr);
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void runtime_MProf_Free(void*, uintptr);
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void runtime_MProf_Mark(void (*scan)(byte *, int64));
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int32 runtime_helpgc(bool*);
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void runtime_gchelper(void);
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// Malloc profiling settings.
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// Must match definition in extern.go.
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enum {
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MProf_None = 0,
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MProf_Sample = 1,
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MProf_All = 2,
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};
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extern int32 runtime_malloc_profile;
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struct __go_func_type;
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bool runtime_getfinalizer(void *p, bool del, void (**fn)(void*), const struct __go_func_type **ft);
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void runtime_walkfintab(void (*fn)(void*), void (*scan)(byte *, int64));
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