linux-kernel - Re: [PATCH] mm/vmstat: retrieve more accurate vmstat value

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Date:	Tue, 24 Nov 2015 09:36:09 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Joonsoo Kim <js1304@...il.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH] mm/vmstat: retrieve more accurate vmstat value

On Tue, 24 Nov 2015, Joonsoo Kim wrote:

> When I tested compaction in low memory condition, I found that
> my benchmark is stuck in congestion_wait() at shrink_inactive_list().
> This stuck last for 1 sec and after then it can escape. More investigation
> shows that it is due to stale vmstat value. vmstat is updated every 1 sec
> so it is stuck for 1 sec.

vmstat values are not designed to be accurate and are not guaranteed to be
accurate. Comparing to specific values should not be done. If you need an
accurate counter then please use another method of accounting like an
atomic.

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