From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> Subject: 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(). Link: http://lkml.kernel.org/r/20200414150233.24495-12-willy@xxxxxxxxxxxxx Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx> Cc: Chao Yu <yuchao0@xxxxxxxxxx> Cc: Cong Wang <xiyou.wangcong@xxxxxxxxx> Cc: Darrick J. Wong <darrick.wong@xxxxxxxxxx> Cc: Dave Chinner <dchinner@xxxxxxxxxx> Cc: Eric Biggers <ebiggers@xxxxxxxxxx> Cc: Gao Xiang <gaoxiang25@xxxxxxxxxx> Cc: Jaegeuk Kim <jaegeuk@xxxxxxxxxx> Cc: Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx> Cc: Junxiao Bi <junxiao.bi@xxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Zi Yan <ziy@xxxxxxxxxx> Cc: Johannes Thumshirn <johannes.thumshirn@xxxxxxx> Cc: Miklos Szeredi <mszeredi@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Documentation/filesystems/locking.rst | 6 +++++- Documentation/filesystems/vfs.rst | 15 +++++++++++++++ include/linux/fs.h | 2 ++ mm/readahead.c | 12 ++++++++++-- 4 files changed, 32 insertions(+), 3 deletions(-) --- a/Documentation/filesystems/locking.rst~mm-add-readahead-address-space-operation +++ a/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. --- a/Documentation/filesystems/vfs.rst~mm-add-readahead-address-space-operation +++ a/Documentation/filesystems/vfs.rst @@ -706,6 +706,7 @@ cache in your filesystem. The following 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 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 --- a/include/linux/fs.h~mm-add-readahead-address-space-operation +++ a/include/linux/fs.h @@ -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, --- a/mm/readahead.c~mm-add-readahead-address-space-operation +++ a/mm/readahead.c @@ -125,7 +125,14 @@ static void read_pages(struct readahead_ 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 a 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; /* _
