Commit 8151b4c8 authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle) Committed by Linus Torvalds
Browse files

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: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: default avatarJohn Hubbard <jhubbard@nvidia.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarWilliam 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: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c1f6925e

Documentation/filesystems/locking.rst

+5 −1
Original line number Diff line number Diff line
@@ -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.

Documentation/filesystems/vfs.rst

+15 −0
Original line number Diff line number Diff line
@@ -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

include/linux/fs.h

+2 −0
Original line number Diff line number Diff line
@@ -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,

mm/readahead.c

+10 −2
Original line number Diff line number Diff line
@@ -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;



	/*

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