mm: introduce delete_from_page_cache()

Presently we increase the page refcount in add_to_page_cache() but don't
decrease it in remove_from_page_cache().  Such asymmetry adds confusion,
requiring that callers notice it and a comment explaining why they release
a page reference.  It's not a good API.

A long time ago, Hugh tried it (http://lkml.org/lkml/2004/10/24/140) but
gave up because reiser4's drop_page() had to unlock the page between
removing it from page cache and doing the page_cache_release().  But now
the situation is changed.  I think at least things in current mainline
don't have any obstacles.  The problem is for out-of-mainline filesystems
- if they have done such things as reiser4, this patch could be a problem
but they will discover this at compile time since we remove
remove_from_page_cache().

This patch:

This function works as just wrapper remove_from_page_cache().  The
difference is that it decreases page references in itself.  So caller have
to make sure it has a page reference before calling.

This patch is ready for removing remove_from_page_cache().

Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Acked-by: Hugh Dickins <hughd@google.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Edward Shishkin <edward.shishkin@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 26946ad..0aa258f 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -455,6 +455,7 @@ int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
 				pgoff_t index, gfp_t gfp_mask);
 int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
 				pgoff_t index, gfp_t gfp_mask);
+extern void delete_from_page_cache(struct page *page);
 extern void remove_from_page_cache(struct page *page);
 extern void __remove_from_page_cache(struct page *page);
 int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask);