From: Roman Gushchin <guro@fb.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Tejun Heo <tj@kernel.org>, Michal Hocko <mhocko@suse.com>,
<linux-mm@kvack.org>, <cgroups@vger.kernel.org>,
<linux-kernel@vger.kernel.org>, <kernel-team@fb.com>
Subject: Re: [PATCH 1/7] mm: memcontrol: fix cpuhotplug statistics flushing
Date: Tue, 2 Feb 2021 18:28:53 -0800 [thread overview]
Message-ID: <20210203022853.GG1812008@carbon.dhcp.thefacebook.com> (raw)
In-Reply-To: <20210202230747.GA1812008@carbon.dhcp.thefacebook.com>
On Tue, Feb 02, 2021 at 03:07:47PM -0800, Roman Gushchin wrote:
> On Tue, Feb 02, 2021 at 01:47:40PM -0500, Johannes Weiner wrote:
> > The memcg hotunplug callback erroneously flushes counts on the local
> > CPU, not the counts of the CPU going away; those counts will be lost.
> >
> > Flush the CPU that is actually going away.
> >
> > Also simplify the code a bit by using mod_memcg_state() and
> > count_memcg_events() instead of open-coding the upward flush - this is
> > comparable to how vmstat.c handles hotunplug flushing.
>
> To the whole series: it's really nice to have an accurate stats at
> non-leaf levels. Just as an illustration: if there are 32 CPUs and
> 1000 sub-cgroups (which is an absolutely realistic number, because
> often there are many dying generations of each cgroup), the error
> margin is 3.9GB. It makes all numbers pretty much random and all
> possible tests extremely flaky.
Btw, I was just looking into kmem kselftests failures/flakiness,
which is caused by exactly this problem: without waiting for the
finish of dying cgroups reclaim, we can't make any reliable assumptions
about what to expect from memcg stats.
So looking forward to have this patchset merged!
next prev parent reply other threads:[~2021-02-03 2:29 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-02 18:47 [PATCH 0/7]: mm: memcontrol: switch to rstat Johannes Weiner
2021-02-02 18:47 ` [PATCH 1/7] mm: memcontrol: fix cpuhotplug statistics flushing Johannes Weiner
2021-02-02 22:23 ` Shakeel Butt
2021-02-02 23:07 ` Roman Gushchin
2021-02-03 2:28 ` Roman Gushchin [this message]
2021-02-04 19:29 ` Johannes Weiner
2021-02-04 19:34 ` Roman Gushchin
2021-02-05 17:50 ` Johannes Weiner
2021-02-04 13:28 ` Michal Hocko
2021-02-02 18:47 ` [PATCH 2/7] mm: memcontrol: kill mem_cgroup_nodeinfo() Johannes Weiner
2021-02-02 22:24 ` Shakeel Butt
2021-02-02 23:13 ` Roman Gushchin
2021-02-04 13:29 ` Michal Hocko
2021-02-02 18:47 ` [PATCH 3/7] mm: memcontrol: privatize memcg_page_state query functions Johannes Weiner
2021-02-02 22:26 ` Shakeel Butt
2021-02-02 23:17 ` Roman Gushchin
2021-02-04 13:30 ` Michal Hocko
2021-02-02 18:47 ` [PATCH 4/7] cgroup: rstat: support cgroup1 Johannes Weiner
2021-02-03 1:16 ` Roman Gushchin
2021-02-04 13:39 ` Michal Hocko
2021-02-04 16:01 ` Johannes Weiner
2021-02-04 16:42 ` Michal Hocko
2021-02-02 18:47 ` [PATCH 5/7] cgroup: rstat: punt root-level optimization to individual controllers Johannes Weiner
2021-02-02 18:47 ` [PATCH 6/7] mm: memcontrol: switch to rstat Johannes Weiner
2021-02-03 1:47 ` Roman Gushchin
2021-02-04 16:26 ` Johannes Weiner
2021-02-04 18:45 ` Roman Gushchin
2021-02-04 20:05 ` Johannes Weiner
2021-02-04 14:19 ` Michal Hocko
2021-02-04 16:15 ` Johannes Weiner
2021-02-04 16:44 ` Michal Hocko
2021-02-04 20:28 ` Johannes Weiner
2021-02-05 15:05 ` Michal Hocko
2021-02-05 16:34 ` Johannes Weiner
2021-02-08 14:07 ` Michal Hocko
2021-02-02 18:47 ` [PATCH 7/7] mm: memcontrol: consolidate lruvec stat flushing Johannes Weiner
2021-02-03 2:25 ` Roman Gushchin
2021-02-04 21:44 ` Johannes Weiner
2021-02-04 21:47 ` Roman Gushchin
2021-02-05 15:17 ` Michal Hocko
2021-02-05 17:10 ` Johannes Weiner
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