linux-kernel - Re: [PATCH] mm,vmscan: Use accurate values for zone

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Date:	Wed, 21 Oct 2015 09:22:40 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, mhocko@...nel.org,
	rientjes@...gle.com, oleg@...hat.com, kwalker@...hat.com,
	akpm@...ux-foundation.org, hannes@...xchg.org,
	vdavydov@...allels.com, skozina@...hat.com, mgorman@...e.de,
	riel@...hat.com
Subject: Re: [PATCH] mm,vmscan: Use accurate values for zone_reclaimable()
 checks

On Wed, 21 Oct 2015, Tetsuo Handa wrote:

> However, if a workqueue which is processed before vmstat_update
> workqueue is processed got stuck inside memory allocation request,
> values in vm_stat_diff[] cannot be merged into vm_stat[]. As a result,
> zone_reclaimable() continues using outdated vm_stat[] values and the
> task which is doing direct reclaim path thinks that there are reclaimable
> pages and therefore continues looping. The consequence is a silent
> livelock (hang up without any kernel messages) because the OOM killer
> will not be invoked.

The diffs will be merged if they reach a certain threshold regardless. You
can decrease that threshhold. See calculate_pressure_threshhold().

Why is the merging not occurring if a process gets stuck? Workrequests are
not blocked by a process being stuck doing memory allocation or reclaim.

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