From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756034AbaJWOwA (ORCPT ); Thu, 23 Oct 2014 10:52:00 -0400 Received: from cantor2.suse.de ([195.135.220.15]:34247 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751899AbaJWOv6 (ORCPT ); Thu, 23 Oct 2014 10:51:58 -0400 Date: Thu, 23 Oct 2014 16:51:56 +0200 From: Michal Hocko To: Johannes Weiner Cc: Andrew Morton , Vladimir Davydov , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [patch 2/2] mm: memcontrol: fix missed end-writeback page accounting Message-ID: <20141023145156.GG23011@dhcp22.suse.cz> References: <1414002568-21042-1-git-send-email-hannes@cmpxchg.org> <1414002568-21042-3-git-send-email-hannes@cmpxchg.org> <20141023130331.GC23011@dhcp22.suse.cz> <20141023141443.GA20526@phnom.home.cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141023141443.GA20526@phnom.home.cmpxchg.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 23-10-14 10:14:43, Johannes Weiner wrote: > On Thu, Oct 23, 2014 at 03:03:31PM +0200, Michal Hocko wrote: > > On Wed 22-10-14 14:29:28, Johannes Weiner wrote: > > > 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API") changed page > > > migration to uncharge the old page right away. The page is locked, > > > unmapped, truncated, and off the LRU, but it could race with writeback > > > ending, which then doesn't unaccount the page properly: > > > > > > test_clear_page_writeback() migration > > > acquire pc->mem_cgroup->move_lock > > > > I do not think that mentioning move_lock is important/helpful here > > because the hot path which is taken all the time (except when there is a > > task move in progress) doesn't take it. > > Besides that it is not even relevant for the race. > > You're right. It's not worth mentioning the transaction setup/finish > at all, because migration does not participate in that protocol. How > about this? Andrew, could you please copy-paste this into the patch? > > test_clear_page_writeback() migration > wait_on_page_writeback() > TestClearPageWriteback() > mem_cgroup_migrate() > clear PCG_USED > mem_cgroup_update_page_stat() > if (PageCgroupUsed(pc)) > decrease memcg pages under writeback Yes, much better! Thanks! -- Michal Hocko SUSE Labs