From ef6a3c63112e865d632ff7c478ba7c7160cad0d1 Mon Sep 17 00:00:00 2001 From: Miklos Szeredi Date: Tue, 22 Mar 2011 16:30:52 -0700 Subject: mm: add replace_page_cache_page() function This function basically does: remove_from_page_cache(old); page_cache_release(old); add_to_page_cache_locked(new); Except it does this atomically, so there's no possibility for the "add" to fail because of a race. If memory cgroups are enabled, then the memory cgroup charge is also moved from the old page to the new. This function is currently used by fuse to move pages into the page cache on read, instead of copying the page contents. [minchan.kim@gmail.com: add freepage() hook to replace_page_cache_page()] Signed-off-by: Miklos Szeredi Acked-by: Rik van Riel Acked-by: KAMEZAWA Hiroyuki Cc: Mel Gorman Signed-off-by: Minchan Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/filemap.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 70 insertions(+) (limited to 'mm/filemap.c') diff --git a/mm/filemap.c b/mm/filemap.c index 312b6eb78430..c1459f2cdb5e 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -386,6 +386,76 @@ int filemap_write_and_wait_range(struct address_space *mapping, } EXPORT_SYMBOL(filemap_write_and_wait_range); +/** + * replace_page_cache_page - replace a pagecache page with a new one + * @old: page to be replaced + * @new: page to replace with + * @gfp_mask: allocation mode + * + * This function replaces a page in the pagecache with a new one. On + * success it acquires the pagecache reference for the new page and + * drops it for the old page. Both the old and new pages must be + * locked. This function does not add the new page to the LRU, the + * caller must do that. + * + * The remove + add is atomic. The only way this function can fail is + * memory allocation failure. + */ +int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask) +{ + int error; + struct mem_cgroup *memcg = NULL; + + VM_BUG_ON(!PageLocked(old)); + VM_BUG_ON(!PageLocked(new)); + VM_BUG_ON(new->mapping); + + /* + * This is not page migration, but prepare_migration and + * end_migration does enough work for charge replacement. + * + * In the longer term we probably want a specialized function + * for moving the charge from old to new in a more efficient + * manner. + */ + error = mem_cgroup_prepare_migration(old, new, &memcg, gfp_mask); + if (error) + return error; + + error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM); + if (!error) { + struct address_space *mapping = old->mapping; + void (*freepage)(struct page *); + + pgoff_t offset = old->index; + freepage = mapping->a_ops->freepage; + + page_cache_get(new); + new->mapping = mapping; + new->index = offset; + + spin_lock_irq(&mapping->tree_lock); + __remove_from_page_cache(old); + error = radix_tree_insert(&mapping->page_tree, offset, new); + BUG_ON(error); + mapping->nrpages++; + __inc_zone_page_state(new, NR_FILE_PAGES); + if (PageSwapBacked(new)) + __inc_zone_page_state(new, NR_SHMEM); + spin_unlock_irq(&mapping->tree_lock); + radix_tree_preload_end(); + if (freepage) + freepage(old); + page_cache_release(old); + mem_cgroup_end_migration(memcg, old, new, true); + } else { + mem_cgroup_end_migration(memcg, old, new, false); + } + + return error; +} +EXPORT_SYMBOL_GPL(replace_page_cache_page); + /** * add_to_page_cache_locked - add a locked page to the pagecache * @page: page to add -- cgit v1.2.3-55-g7522