Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756088Ab3EQUjO (ORCPT ); Fri, 17 May 2013 16:39:14 -0400 Received: from zene.cmpxchg.org ([85.214.230.12]:45186 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755902Ab3EQUjM (ORCPT ); Fri, 17 May 2013 16:39:12 -0400 Date: Fri, 17 May 2013 16:39:02 -0400 From: Johannes Weiner To: Mel Gorman Cc: Alexey Lyahkov , Andrew Perepechko , Robin Dong , Theodore Tso , Andrew Morton , Hugh Dickins , Rik van Riel , Bernd Schubert , David Howells , Trond Myklebust , Linux-fsdevel , Linux-ext4 , LKML , Linux-mm Subject: Re: [PATCH 3/5] mm: Activate !PageLRU pages on mark_page_accessed if page is on local pagevec Message-ID: <20130517203902.GB15721@cmpxchg.org> References: <1368784087-956-1-git-send-email-mgorman@suse.de> <1368784087-956-4-git-send-email-mgorman@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1368784087-956-4-git-send-email-mgorman@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2374 Lines: 49 On Fri, May 17, 2013 at 10:48:05AM +0100, Mel Gorman wrote: > If a page is on a pagevec then it is !PageLRU and mark_page_accessed() > may fail to move a page to the active list as expected. Now that the LRU > is selected at LRU drain time, mark pages PageActive if they are on the > local pagevec so it gets moved to the correct list at LRU drain time. > Using a debugging patch it was found that for a simple git checkout based > workload that pages were never added to the active file list in practice > but with this patch applied they are. > > before after > LRU Add Active File 0 750583 > LRU Add Active Anon 2640587 2702818 > LRU Add Inactive File 8833662 8068353 > LRU Add Inactive Anon 207 200 > > Note that only pages on the local pagevec are considered on purpose. A > !PageLRU page could be in the process of being released, reclaimed, migrated > or on a remote pagevec that is currently being drained. Marking it PageActive > is vunerable to races where PageLRU and Active bits are checked at the > wrong time. Page reclaim will trigger VM_BUG_ONs but depending on when the > race hits, it could also free a PageActive page to the page allocator and > trigger a bad_page warning. Similarly a potential race exists between a > per-cpu drain on a pagevec list and an activation on a remote CPU. > > lru_add_drain_cpu > __pagevec_lru_add > lru = page_lru(page); > mark_page_accessed > if (PageLRU(page)) > activate_page > else > SetPageActive > SetPageLRU(page); > add_page_to_lru_list(page, lruvec, lru); > > In this case a PageActive page is added to the inactivate list and later the > inactive/active stats will get skewed. While the PageActive checks in vmscan > could be removed and potentially dealt with, a skew in the statistics would > be very difficult to detect. Hence this patch deals just with the common case > where a page being marked accessed has just been added to the local pagevec. > > Signed-off-by: Mel Gorman Acked-by: Johannes Weiner -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/