From 042124cc64c33555deba0b11c6e0c612ae7a8653 Mon Sep 17 00:00:00 2001 From: "Matthew Wilcox (Oracle)" Date: Mon, 1 Jun 2020 21:46:21 -0700 Subject: [PATCH] mm: add new readahead_control API Filesystems which implement the upcoming ->readahead method will get their pages by calling readahead_page() or readahead_page_batch(). These functions support large pages, even though none of the filesystems to be converted do yet. Signed-off-by: Matthew Wilcox (Oracle) Signed-off-by: Andrew Morton Reviewed-by: Christoph Hellwig Reviewed-by: William Kucharski Cc: Chao Yu Cc: Cong Wang Cc: Darrick J. Wong Cc: Dave Chinner Cc: Eric Biggers Cc: Gao Xiang Cc: Jaegeuk Kim Cc: John Hubbard Cc: Joseph Qi Cc: Junxiao Bi Cc: Michal Hocko Cc: Zi Yan Cc: Johannes Thumshirn Cc: Miklos Szeredi Link: http://lkml.kernel.org/r/20200414150233.24495-6-willy@infradead.org Signed-off-by: Linus Torvalds --- include/linux/pagemap.h | 140 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 140 insertions(+) diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 8c081cda4b35..c3bf73263ec9 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -642,6 +642,146 @@ static inline int add_to_page_cache(struct page *page, return error; } +/** + * struct readahead_control - Describes a readahead request. + * + * A readahead request is for consecutive pages. Filesystems which + * implement the ->readahead method should call readahead_page() or + * readahead_page_batch() in a loop and attempt to start I/O against + * each page in the request. + * + * Most of the fields in this struct are private and should be accessed + * by the functions below. + * + * @file: The file, used primarily by network filesystems for authentication. + * May be NULL if invoked internally by the filesystem. + * @mapping: Readahead this filesystem object. + */ +struct readahead_control { + struct file *file; + struct address_space *mapping; +/* private: use the readahead_* accessors instead */ + pgoff_t _index; + unsigned int _nr_pages; + unsigned int _batch_count; +}; + +/** + * readahead_page - Get the next page to read. + * @rac: The current readahead request. + * + * Context: The page is locked and has an elevated refcount. The caller + * should decreases the refcount once the page has been submitted for I/O + * and unlock the page once all I/O to that page has completed. + * Return: A pointer to the next page, or %NULL if we are done. + */ +static inline struct page *readahead_page(struct readahead_control *rac) +{ + struct page *page; + + BUG_ON(rac->_batch_count > rac->_nr_pages); + rac->_nr_pages -= rac->_batch_count; + rac->_index += rac->_batch_count; + + if (!rac->_nr_pages) { + rac->_batch_count = 0; + return NULL; + } + + page = xa_load(&rac->mapping->i_pages, rac->_index); + VM_BUG_ON_PAGE(!PageLocked(page), page); + rac->_batch_count = hpage_nr_pages(page); + + return page; +} + +static inline unsigned int __readahead_batch(struct readahead_control *rac, + struct page **array, unsigned int array_sz) +{ + unsigned int i = 0; + XA_STATE(xas, &rac->mapping->i_pages, 0); + struct page *page; + + BUG_ON(rac->_batch_count > rac->_nr_pages); + rac->_nr_pages -= rac->_batch_count; + rac->_index += rac->_batch_count; + rac->_batch_count = 0; + + xas_set(&xas, rac->_index); + rcu_read_lock(); + xas_for_each(&xas, page, rac->_index + rac->_nr_pages - 1) { + VM_BUG_ON_PAGE(!PageLocked(page), page); + VM_BUG_ON_PAGE(PageTail(page), page); + array[i++] = page; + rac->_batch_count += hpage_nr_pages(page); + + /* + * The page cache isn't using multi-index entries yet, + * so the xas cursor needs to be manually moved to the + * next index. This can be removed once the page cache + * is converted. + */ + if (PageHead(page)) + xas_set(&xas, rac->_index + rac->_batch_count); + + if (i == array_sz) + break; + } + rcu_read_unlock(); + + return i; +} + +/** + * readahead_page_batch - Get a batch of pages to read. + * @rac: The current readahead request. + * @array: An array of pointers to struct page. + * + * Context: The pages are locked and have an elevated refcount. The caller + * should decreases the refcount once the page has been submitted for I/O + * and unlock the page once all I/O to that page has completed. + * Return: The number of pages placed in the array. 0 indicates the request + * is complete. + */ +#define readahead_page_batch(rac, array) \ + __readahead_batch(rac, array, ARRAY_SIZE(array)) + +/** + * readahead_pos - The byte offset into the file of this readahead request. + * @rac: The readahead request. + */ +static inline loff_t readahead_pos(struct readahead_control *rac) +{ + return (loff_t)rac->_index * PAGE_SIZE; +} + +/** + * readahead_length - The number of bytes in this readahead request. + * @rac: The readahead request. + */ +static inline loff_t readahead_length(struct readahead_control *rac) +{ + return (loff_t)rac->_nr_pages * PAGE_SIZE; +} + +/** + * readahead_index - The index of the first page in this readahead request. + * @rac: The readahead request. + */ +static inline pgoff_t readahead_index(struct readahead_control *rac) +{ + return rac->_index; +} + +/** + * readahead_count - The number of pages in this readahead request. + * @rac: The readahead request. + */ +static inline unsigned int readahead_count(struct readahead_control *rac) +{ + return rac->_nr_pages; +} + static inline unsigned long dir_pages(struct inode *inode) { return (unsigned long)(inode->i_size + PAGE_SIZE - 1) >> -- GitLab