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>
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 @@
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);
diff --git a/mm/filemap.c b/mm/filemap.c
index c1459f2..e7b5978 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -155,6 +155,22 @@
}
EXPORT_SYMBOL(remove_from_page_cache);
+/**
+ * delete_from_page_cache - delete page from page cache
+ * @page: the page which the kernel is trying to remove from page cache
+ *
+ * This must be called only on pages that have
+ * been verified to be in the page cache and locked.
+ * It will never put the page into the free list,
+ * the caller has a reference on the page.
+ */
+void delete_from_page_cache(struct page *page)
+{
+ remove_from_page_cache(page);
+ page_cache_release(page);
+}
+EXPORT_SYMBOL(delete_from_page_cache);
+
static int sync_page(void *word)
{
struct address_space *mapping;
