linux-kernel - Re: [patch 0/3] mm: improve page aging fairness between zones/nodes

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Date:	Wed, 24 Jul 2013 13:18:35 +0200
From:	Zlatko Calusic <zcalusic@...sync.net>
To:	Johannes Weiner <hannes@...xchg.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 0/3] mm: improve page aging fairness between zones/nodes

On 22.07.2013 18:48, Zlatko Calusic wrote:
> On 19.07.2013 22:55, Johannes Weiner wrote:
>> The way the page allocator interacts with kswapd creates aging
>> imbalances, where the amount of time a userspace page gets in memory
>> under reclaim pressure is dependent on which zone, which node the
>> allocator took the page frame from.
>>
>> #1 fixes missed kswapd wakeups on NUMA systems, which lead to some
>>     nodes falling behind for a full reclaim cycle relative to the other
>>     nodes in the system
>>
>> #3 fixes an interaction where kswapd and a continuous stream of page
>>     allocations keep the preferred zone of a task between the high and
>>     low watermark (allocations succeed + kswapd does not go to sleep)
>>     indefinitely, completely underutilizing the lower zones and
>>     thrashing on the preferred zone
>>
>> These patches are the aging fairness part of the thrash-detection
>> based file LRU balancing.  Andrea recommended to submit them
>> separately as they are bugfixes in their own right.
>>
>
> I have the patch applied and under testing. So far, so good. It looks
> like it could finally fix the bug that I was chasing few months ago
> (nicely described in your bullet #3). But, few more days of testing will
> be needed before I can reach a quality verdict.
>

Well, only 2 days later it's already obvious that the patch is perfect! :)

In the attached image, in the left column are the graphs covering last 
day and a half. It can be observed that zones are really balanced, and 
that aging is practically perfect. Graphs on the right column cover last 
10 day period, and the left side of the upper graph shows how it would 
look with the stock kernel after about 20 day uptime (although only a 
few days is enough to reach such imbalance). File pages in the Normal 
zone are extinct species (red) and the zone is choke full of anon pages 
(blue). Having seen a lot of this graphs, I'm certain that it won't 
happen anymore with your patch applied. The balance is restored! Thank 
you for your work. Feel free to add:

Tested-by: Zlatko Calusic <zcalusic@...sync.net>

Regards,
-- 
Zlatko

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