From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [patch 2/2] mm: memcontrol: fix missed end-writeback page accounting Date: Thu, 23 Oct 2014 16:51:56 +0200 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 Return-path: Content-Disposition: inline In-Reply-To: <20141023141443.GA20526-HTCKtW7iVlxqnrmGgq4/JMIURNUf+fel@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Johannes Weiner Cc: Andrew Morton , Vladimir Davydov , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.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