From: Roman Gushchin <guro@fb.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-mm@kvack.org, Tejun Heo <tj@kernel.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
kernel-team@fb.com, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm, memcg: reset low limit during memcg offlining
Date: Tue, 25 Jul 2017 13:06:42 +0100 [thread overview]
Message-ID: <20170725120642.GA12635@castle.DHCP.thefacebook.com> (raw)
In-Reply-To: <20170725115808.GE26723@dhcp22.suse.cz>
On Tue, Jul 25, 2017 at 01:58:08PM +0200, Michal Hocko wrote:
> On Tue 25-07-17 12:40:47, Roman Gushchin wrote:
> > A removed memory cgroup with a defined low limit and some belonging
> > pagecache has very low chances to be freed.
> >
> > If a cgroup has been removed, there is likely no memory pressure inside
> > the cgroup, and the pagecache is protected from the external pressure
> > by the defined low limit. The cgroup will be freed only after
> > the reclaim of all belonging pages. And it will not happen until
> > there are any reclaimable memory in the system. That means,
> > there is a good chance, that a cold pagecache will reside
> > in the memory for an undefined amount of time, wasting
> > system resources.
> >
> > Fix this issue by zeroing memcg->low during memcg offlining.
>
> Very well spotted! This goes all the way down to low limit inclusion
> AFAICS. I would be even tempted to mark it for stable because hiding
> some memory from reclaim basically indefinitely is not good. We might
> have been just lucky nobody has noticed that yet.
I believe it's because there are not so many actual low limit users,
and those who do, are using some offstream patches to mitigate this issue.
Thanks!
Roman
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next prev parent reply other threads:[~2017-07-25 12:07 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-25 11:40 [PATCH] mm, memcg: reset low limit during memcg offlining Roman Gushchin
2017-07-25 11:58 ` Michal Hocko
2017-07-25 12:06 ` Roman Gushchin [this message]
2017-07-25 12:05 ` Vladimir Davydov
2017-07-25 12:31 ` Roman Gushchin
2017-07-25 12:44 ` Michal Hocko
2017-07-26 8:30 ` Vladimir Davydov
2017-07-26 12:06 ` Tejun Heo
2017-07-27 13:04 ` [PATCH 1/2] mm, memcg: reset memory.low " Roman Gushchin
2017-07-27 13:04 ` [PATCH 2/2] cgroup: revert fa06235b8eb0 ("cgroup: reset css on destruction") Roman Gushchin
2017-07-27 13:52 ` Tejun Heo
2017-07-27 14:36 ` Johannes Weiner
2017-07-27 14:35 ` [PATCH 1/2] mm, memcg: reset memory.low during memcg offlining Johannes Weiner
2017-07-27 14:47 ` Michal Hocko
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