From: Andrew Morton <akpm@linux-foundation.org>
To: Roman Gushchin <guro@fb.com>
Cc: <linux-mm@kvack.org>, Michal Hocko <mhocko@kernel.org>,
Johannes Weiner <hannes@cmpxchg.org>,
<linux-kernel@vger.kernel.org>, <kernel-team@fb.com>,
Vladimir Davydov <vdavydov.dev@gmail.com>
Subject: Re: [PATCH v2 2/3] mm: memcontrol: flush percpu slab vmstats on kmem offlining
Date: Mon, 19 Aug 2019 15:27:44 -0700 [thread overview]
Message-ID: <20190819152744.4ab8478cfb8697856408425b@linux-foundation.org> (raw)
In-Reply-To: <20190819202338.363363-3-guro@fb.com>
On Mon, 19 Aug 2019 13:23:37 -0700 Roman Gushchin <guro@fb.com> wrote:
> I've noticed that the "slab" value in memory.stat is sometimes 0,
> even if some children memory cgroups have a non-zero "slab" value.
> The following investigation showed that this is the result
> of the kmem_cache reparenting in combination with the per-cpu
> batching of slab vmstats.
>
> At the offlining some vmstat value may leave in the percpu cache,
> not being propagated upwards by the cgroup hierarchy. It means
> that stats on ancestor levels are lower than actual. Later when
> slab pages are released, the precise number of pages is substracted
> on the parent level, making the value negative. We don't show negative
> values, 0 is printed instead.
>
> To fix this issue, let's flush percpu slab memcg and lruvec stats
> on memcg offlining. This guarantees that numbers on all ancestor
> levels are accurate and match the actual number of outstanding
> slab pages.
>
> Fixes: fb2f2b0adb98 ("mm: memcg/slab: reparent memcg kmem_caches on cgroup removal")
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
[1/3] and [3/3] have cc:stable. [2/3] does not. However [3/3] does
not correctly apply without [2/3] having being applied.
next prev parent reply other threads:[~2019-08-19 22:27 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-19 20:23 [PATCH v2 0/3] vmstats/vmevents flushing Roman Gushchin
2019-08-19 20:23 ` [PATCH v2 1/3] mm: memcontrol: flush percpu vmstats before releasing memcg Roman Gushchin
2019-08-19 20:23 ` [PATCH v2 2/3] mm: memcontrol: flush percpu slab vmstats on kmem offlining Roman Gushchin
2019-08-19 22:27 ` Andrew Morton [this message]
2019-08-19 22:46 ` Roman Gushchin
2019-08-19 20:23 ` [PATCH v2 3/3] mm: memcontrol: flush percpu vmevents before releasing memcg Roman Gushchin
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