From: Michal Hocko <mhocko@suse.cz>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Vladimir Davydov <vdavydov@parallels.com>,
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
Date: Thu, 23 Oct 2014 16:51:56 +0200 [thread overview]
Message-ID: <20141023145156.GG23011@dhcp22.suse.cz> (raw)
In-Reply-To: <20141023141443.GA20526@phnom.home.cmpxchg.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
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prev parent reply other threads:[~2014-10-23 14:52 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-22 18:29 [patch 0/2] mm: memcontrol: fix race between migration and writeback Johannes Weiner
2014-10-22 18:29 ` [patch 1/2] mm: page-writeback: inline account_page_dirtied() into single caller Johannes Weiner
2014-10-23 12:21 ` Michal Hocko
2014-10-22 18:29 ` [patch 2/2] mm: memcontrol: fix missed end-writeback page accounting Johannes Weiner
2014-10-22 20:39 ` Andrew Morton
2014-10-23 13:54 ` Johannes Weiner
2014-10-23 15:00 ` Michal Hocko
2014-10-23 13:57 ` Johannes Weiner
2014-10-23 15:03 ` Michal Hocko
2014-10-23 13:03 ` Michal Hocko
2014-10-23 14:14 ` Johannes Weiner
2014-10-23 14:51 ` Michal Hocko [this message]
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