linux-kernel - Re: [PATCH v2] mm: vmscan: fix the page state calculation in too_many

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Date:	Wed, 14 Jan 2015 17:50:36 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Vinayak Menon <vinmenon@...eaurora.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, hannes@...xchg.org,
	vdavydov@...allels.com, mgorman@...e.de, minchan@...nel.org
Subject: Re: [PATCH v2] mm: vmscan: fix the page state calculation in
 too_many_isolated

On Wed 14-01-15 17:06:59, Vinayak Menon wrote:
[...]
> In one such instance, zone_page_state(zone, NR_ISOLATED_FILE)
> had returned 14, zone_page_state(zone, NR_INACTIVE_FILE)
> returned 92, and GFP_IOFS was set, and this resulted
> in too_many_isolated returning true. But one of the CPU's
> pageset vm_stat_diff had NR_ISOLATED_FILE as "-14". So the
> actual isolated count was zero. As there weren't any more
> updates to NR_ISOLATED_FILE and vmstat_update deffered work
> had not been scheduled yet, 7 tasks were spinning in the
> congestion wait loop for around 4 seconds, in the direct
> reclaim path.

Not syncing for such a long time doesn't sound right. I am not familiar
with the vmstat syncing but sysctl_stat_interval is HZ so it should
happen much more often that every 4 seconds.

-- 
Michal Hocko
SUSE Labs
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