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authorMatthew Wilcox (Oracle) <willy@infradead.org>2020-06-01 21:46:44 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-06-02 10:59:06 -0700
commit8151b4c8bee43cea7a28cb0300123df90880e60c (patch)
tree4a9fe88f77cb4ab637628372b90ffe0baf00e9a8 /Documentation
parentc1f6925e10912c7e329840387730049e5e1848c8 (diff)
mm: add readahead address space operation
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>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/filesystems/locking.rst6
-rw-r--r--Documentation/filesystems/vfs.rst15
2 files changed, 20 insertions, 1 deletions
diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
index 5057e4d9dcd1..0af2e0e11461 100644
--- a/Documentation/filesystems/locking.rst
+++ b/Documentation/filesystems/locking.rst
@@ -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.
diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index 7d4d09dd5e6d..ed17771c212b 100644
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -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