From: Johannes Weiner <hannes@cmpxchg.org>
To: Shakeel Butt <shakeelb@google.com>
Cc: Mel Gorman <mgorman@suse.de>, Roman Gushchin <guro@fb.com>,
Michal Hocko <mhocko@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Yafang Shao <laoar.shao@gmail.com>,
linux-mm@kvack.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] memcg: expose root cgroup's memory.stat
Date: Fri, 8 May 2020 17:44:05 -0400 [thread overview]
Message-ID: <20200508214405.GA226164@cmpxchg.org> (raw)
In-Reply-To: <20200508170630.94406-1-shakeelb@google.com>
On Fri, May 08, 2020 at 10:06:30AM -0700, Shakeel Butt wrote:
> One way to measure the efficiency of memory reclaim is to look at the
> ratio (pgscan+pfrefill)/pgsteal. However at the moment these stats are
> not updated consistently at the system level and the ratio of these are
> not very meaningful. The pgsteal and pgscan are updated for only global
> reclaim while pgrefill gets updated for global as well as cgroup
> reclaim.
>
> Please note that this difference is only for system level vmstats. The
> cgroup stats returned by memory.stat are actually consistent. The
> cgroup's pgsteal contains number of reclaimed pages for global as well
> as cgroup reclaim. So, one way to get the system level stats is to get
> these stats from root's memory.stat, so, expose memory.stat for the root
> cgroup.
>
> from Johannes Weiner:
> There are subtle differences between /proc/vmstat and
> memory.stat, and cgroup-aware code that wants to watch the full
> hierarchy currently has to know about these intricacies and
> translate semantics back and forth.
>
> Generally having the fully recursive memory.stat at the root
> level could help a broader range of usecases.
The changelog begs the question why we don't just "fix" the
system-level stats. It may be useful to include the conclusions from
that discussion, and why there is value in keeping the stats this way.
> Signed-off-by: Shakeel Butt <shakeelb@google.com>
> Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
next prev parent reply other threads:[~2020-05-08 21:44 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-08 17:06 [PATCH] memcg: expose root cgroup's memory.stat Shakeel Butt
2020-05-08 21:44 ` Johannes Weiner [this message]
2020-05-09 14:06 ` Shakeel Butt
2020-05-09 14:43 ` Yafang Shao
2020-05-15 8:29 ` Michal Hocko
2020-05-15 13:24 ` Johannes Weiner
2020-05-15 13:44 ` Shakeel Butt
2020-05-15 15:00 ` Roman Gushchin
2020-05-15 17:49 ` Shakeel Butt
2020-05-15 18:09 ` Johannes Weiner
2020-05-16 0:13 ` Shakeel Butt
2020-05-15 18:09 ` Roman Gushchin
2020-05-16 0:06 ` Shakeel Butt
2020-05-16 1:42 ` Chris Down
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