From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760580AbbA1Btc (ORCPT ); Tue, 27 Jan 2015 20:49:32 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:41426 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933341AbbA1Bif (ORCPT ); Tue, 27 Jan 2015 20:38:35 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Mel Gorman , Johannes Weiner , Vlastimil Babka , Jan Kara , Michal Hocko , Hugh Dickins , Dave Hansen , Theodore Tso , "Paul E. McKenney" , Oleg Nesterov , Rik van Riel , Peter Zijlstra , Andrew Morton , Linus Torvalds Subject: [PATCH 3.14 60/77] mm: do not use unnecessary atomic operations when adding pages to the LRU Date: Tue, 27 Jan 2015 17:27:38 -0800 Message-Id: <20150128012747.767246625@linuxfoundation.org> X-Mailer: git-send-email 2.2.2 In-Reply-To: <20150128012745.971137091@linuxfoundation.org> References: <20150128012745.971137091@linuxfoundation.org> User-Agent: quilt/0.63-1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Mel Gorman commit 6fb81a17d21f2a138b8f424af4cf379f2b694060 upstream. When adding pages to the LRU we clear the active bit unconditionally. As the page could be reachable from other paths we cannot use unlocked operations without risk of corruption such as a parallel mark_page_accessed. This patch tests if is necessary to clear the active flag before using an atomic operation. This potentially opens a tiny race when PageActive is checked as mark_page_accessed could be called after PageActive was checked. The race already exists but this patch changes it slightly. The consequence is that that the page may be promoted to the active list that might have been left on the inactive list before the patch. It's too tiny a race and too marginal a consequence to always use atomic operations for. Signed-off-by: Mel Gorman Acked-by: Johannes Weiner Cc: Vlastimil Babka Cc: Jan Kara Cc: Michal Hocko Cc: Hugh Dickins Cc: Dave Hansen Cc: Theodore Ts'o Cc: "Paul E. McKenney" Cc: Oleg Nesterov Cc: Rik van Riel Cc: Peter Zijlstra Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Mel Gorman Signed-off-by: Greg Kroah-Hartman --- mm/swap.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) --- a/mm/swap.c +++ b/mm/swap.c @@ -597,13 +597,15 @@ static void __lru_cache_add(struct page */ void lru_cache_add_anon(struct page *page) { - ClearPageActive(page); + if (PageActive(page)) + ClearPageActive(page); __lru_cache_add(page); } void lru_cache_add_file(struct page *page) { - ClearPageActive(page); + if (PageActive(page)) + ClearPageActive(page); __lru_cache_add(page); } EXPORT_SYMBOL(lru_cache_add_file);