Date: Wed, 25 Nov 2015 14:47:52 +0100
From: Michal Hocko <mhocko@kernel.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Joonsoo Kim <js1304@gmail.com>, Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, Christoph Lameter <cl@linux.com>,
        linux-mm@kvack.org, Joonsoo Kim <iamjoonsoo.kim@lge.com>
Subject: Re: [PATCH] mm/vmstat: retrieve more accurate vmstat value
Message-ID: <20151125134747.GH27283@dhcp22.suse.cz>
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 <5655BB0A.90000@suse.cz>
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On Wed 25-11-15 14:43:38, Vlastimil Babka wrote:
> On 11/25/2015 01:00 PM, Michal Hocko wrote:
> > On Tue 24-11-15 15:22:03, 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.
> > 
> > Wouldn't it be sufficient to use zone_page_state_snapshot in
> > too_many_isolated?
> 
> That sounds better than the ad-hoc half-solution, yeah.
> I don't know how performance sensitive the callers are, but maybe it could do a
> non-snapshot check first, and only repeat with _snapshot when it's about to wait
> (the result is true), just to make sure?

I am not sure this is worth bothering. We are in the reclaim which is
not a hot path.

-- 
Michal Hocko
SUSE Labs
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