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mm: add readahead address space operation

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This replaces ->readpages with a saner interface:
 - Return void instead of an ignored error code.
 - Page cache is already populated with locked pages when ->readahead
   is called.
 - New arguments can be passed to the implementation without changing
   all the filesystems that use a common helper function like
   mpage_readahead().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200414150233.24495-12-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Matthew Wilcox (Oracle) 2020-06-01 21:46:44 -07:00 committed by Linus Torvalds
parent c1f6925e10
commit 8151b4c8be
4 changed files with 32 additions and 3 deletions
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6
Documentation/filesystems/locking.rst
View File

@ -239,6 +239,7 @@ prototypes::
int (*readpage)(struct file *, struct page *);
int (*writepages)(struct address_space *, struct writeback_control *);
int (*set_page_dirty)(struct page *page);
void (*readahead)(struct readahead_control *);
int (*readpages)(struct file *filp, struct address_space *mapping,
struct list_head *pages, unsigned nr_pages);
int (*write_begin)(struct file *, struct address_space *mapping,
@ -271,7 +272,8 @@ writepage: yes, unlocks (see below)
readpage: yes, unlocks
writepages:
set_page_dirty no
readpages:
readahead: yes, unlocks
readpages: no
write_begin: locks the page exclusive
write_end: yes, unlocks exclusive
bmap:
@ -295,6 +297,8 @@ the request handler (/dev/loop).
->readpage() unlocks the page, either synchronously or via I/O
completion.
->readahead() unlocks the pages that I/O is attempted on like ->readpage().
->readpages() populates the pagecache with the passed pages and starts
I/O against them. They come unlocked upon I/O completion.

15
Documentation/filesystems/vfs.rst
View File

@ -706,6 +706,7 @@ cache in your filesystem. The following members are defined:
int (*readpage)(struct file *, struct page *);
int (*writepages)(struct address_space *, struct writeback_control *);
int (*set_page_dirty)(struct page *page);
void (*readahead)(struct readahead_control *);
int (*readpages)(struct file *filp, struct address_space *mapping,
struct list_head *pages, unsigned nr_pages);
int (*write_begin)(struct file *, struct address_space *mapping,
@ -781,12 +782,26 @@ cache in your filesystem. The following members are defined:
If defined, it should set the PageDirty flag, and the
PAGECACHE_TAG_DIRTY tag in the radix tree.
``readahead``
Called by the VM to read pages associated with the address_space
object. The pages are consecutive in the page cache and are
locked. The implementation should decrement the page refcount
after starting I/O on each page. Usually the page will be
unlocked by the I/O completion handler. If the filesystem decides
to stop attempting I/O before reaching the end of the readahead
window, it can simply return. The caller will decrement the page
refcount and unlock the remaining pages for you. Set PageUptodate
if the I/O completes successfully. Setting PageError on any page
will be ignored; simply unlock the page if an I/O error occurs.
``readpages``
called by the VM to read pages associated with the address_space
object. This is essentially just a vector version of readpage.
Instead of just one page, several pages are requested.
readpages is only used for read-ahead, so read errors are
ignored. If anything goes wrong, feel free to give up.
This interface is deprecated and will be removed by the end of
2020; implement readahead instead.
``write_begin``
Called by the generic buffered write code to ask the filesystem

2
include/linux/fs.h
View File

@ -292,6 +292,7 @@ enum positive_aop_returns {
struct page;
struct address_space;
struct writeback_control;
struct readahead_control;
/*
* Write life time hint values.
@ -375,6 +376,7 @@ struct address_space_operations {
*/
int (*readpages)(struct file *filp, struct address_space *mapping,
struct list_head *pages, unsigned nr_pages);
void (*readahead)(struct readahead_control *);
int (*write_begin)(struct file *, struct address_space *mapping,
loff_t pos, unsigned len, unsigned flags,

12
mm/readahead.c
View File

@ -125,7 +125,14 @@ static void read_pages(struct readahead_control *rac, struct list_head *pages,
blk_start_plug(&plug);
if (aops->readpages) {
if (aops->readahead) {
aops->readahead(rac);
/* Clean up the remaining pages */
while ((page = readahead_page(rac))) {
unlock_page(page);
put_page(page);
}
} else if (aops->readpages) {
aops->readpages(rac->file, rac->mapping, pages,
readahead_count(rac));
/* Clean up the remaining pages */
@ -233,7 +240,8 @@ void force_page_cache_readahead(struct address_space *mapping,
struct file_ra_state *ra = &filp->f_ra;
unsigned long max_pages;
if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages &&
!mapping->a_ops->readahead))
return;
/*