linux-kernel - Re: [PATCH 1/2] mm: add per-zone lru list stat

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Date:	Wed, 20 Jul 2016 11:55:49 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm: add per-zone lru list stat

On Wed, Jul 20, 2016 at 09:16:24AM +0900, Minchan Kim wrote:
> On Tue, Jul 19, 2016 at 05:48:57PM +0100, Mel Gorman wrote:
> > On Wed, Jul 20, 2016 at 12:50:32AM +0900, Minchan Kim wrote:
> > > While I did stress test with hackbench, I got OOM message frequently
> > > which didn't ever happen in zone-lru.
> > > 
> > 
> > This one also showed pgdat going unreclaimable early. Have you tried any
> > of the three oom-related patches I sent to Joonsoo to see what impact,
> > if any, it had?
> 
> Before the result, I want to say goal of this patch, again.
> Without per-zone lru stat, it's really hard to debug OOM problem in
> multiple zones system so regardless of solving the problem, we should add
> per-zone lru stat for debuggability of OOM which has been never perfect
> solution, ever.
> 

That's not in dispute, I simply wanted to know the impact.

> The result is not OOM but hackbench stalls forever.

Ok, that points to both the premature marking pgdats as unreclaimable
and the inactive rotation are both problems.

I have a series prepared that may or may not address the problem. I'm
trying to reproduce the OOM killer on a 32-bit KVM but so far so luck.
If I fail to reproduce it then I cannot tell if the series has an impact
and may have to post it and hope you and Joonsoo can test it.

-- 
Mel Gorman
SUSE Labs