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Date:   Thu, 7 May 2020 15:28:56 -0700
From:   Roman Gushchin <guro@fb.com>
To:     Shakeel Butt <shakeelb@google.com>
CC:     Mel Gorman <mgorman@suse.de>, Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: vmscan: consistent update to pgsteal and pgscan
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On Thu, May 07, 2020 at 01:49:13PM -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 but root does not expose that
> interface. Also for !CONFIG_MEMCG machines /proc/vmstat is the only way
> to get these stats. So, make these stats consistent.
> 
> Signed-off-by: Shakeel Butt <shakeelb@google.com>

Acked-by: Roman Gushchin <guro@fb.com>

Thanks!