From 9057c212b93709fa54e62d434502a64591cfa5e6 Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Thu, 28 Aug 2014 19:35:33 +0100 Subject: [PATCH] mm: avoid unnecessary atomic operations during end_page_writeback() commit 888cf2db475a256fb0cda042140f73d7881f81fe upstream. If a page is marked for immediate reclaim then it is moved to the tail of the LRU list. This occurs when the system is under enough memory pressure for pages under writeback to reach the end of the LRU but we test for this using atomic operations on every writeback. This patch uses an optimistic non-atomic test first. It'll miss some pages in rare cases but the consequences are not severe enough to warrant such a penalty. While the function does not dominate profiles during a simple dd test the cost of it is reduced. 73048 0.7428 vmlinux-3.15.0-rc5-mmotm-20140513 end_page_writeback 23740 0.2409 vmlinux-3.15.0-rc5-lessatomic end_page_writeback Signed-off-by: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Mel Gorman Signed-off-by: Jiri Slaby --- mm/filemap.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/mm/filemap.c b/mm/filemap.c index 115c77d..b012dae 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -644,8 +644,17 @@ EXPORT_SYMBOL(unlock_page); */ void end_page_writeback(struct page *page) { - if (TestClearPageReclaim(page)) + /* + * TestClearPageReclaim could be used here but it is an atomic + * operation and overkill in this particular case. Failing to + * shuffle a page marked for immediate reclaim is too mild to + * justify taking an atomic operation penalty at the end of + * ever page writeback. + */ + if (PageReclaim(page)) { + ClearPageReclaim(page); rotate_reclaimable_page(page); + } if (!test_clear_page_writeback(page)) BUG(); -- 1.9.1