From: Wu Fengguang Introduce a pair of functions to probe the existence of file page. - int __probe_page(mapping, offset) - int probe_page(mapping, offset) Signed-off-by: Wu Fengguang Signed-off-by: Andrew Morton --- include/linux/pagemap.h | 2 ++ mm/filemap.c | 23 +++++++++++++++++++++++ 2 files changed, 25 insertions(+) diff -puN include/linux/pagemap.h~mm-introduce-probe_page include/linux/pagemap.h --- a/include/linux/pagemap.h~mm-introduce-probe_page +++ a/include/linux/pagemap.h @@ -83,6 +83,8 @@ static inline struct page *page_cache_al typedef int filler_t(void *, struct page *); +extern int __probe_page(struct address_space *mapping, pgoff_t offset); +extern int probe_page(struct address_space *mapping, pgoff_t offset); extern struct page * find_get_page(struct address_space *mapping, unsigned long index); extern struct page * find_lock_page(struct address_space *mapping, diff -puN mm/filemap.c~mm-introduce-probe_page mm/filemap.c --- a/mm/filemap.c~mm-introduce-probe_page +++ a/mm/filemap.c @@ -645,6 +645,29 @@ repeat: } EXPORT_SYMBOL(find_lock_page); +/* + * Probing page existence. + */ +int __probe_page(struct address_space *mapping, pgoff_t offset) +{ + return !!radix_tree_lookup(&mapping->page_tree, offset); +} + +/* + * Here we just do not bother to grab the page, it's meaningless anyway. + */ +int probe_page(struct address_space *mapping, pgoff_t offset) +{ + int exists; + + read_lock_irq(&mapping->tree_lock); + exists = __probe_page(mapping, offset); + read_unlock_irq(&mapping->tree_lock); + + return exists; +} +EXPORT_SYMBOL(probe_page); + /** * find_or_create_page - locate or add a pagecache page * @mapping: the page's address_space _