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

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Date:	Mon, 22 Jul 2013 13:01:12 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	Zlatko Calusic <zcalusic@...sync.net>
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

Hi Zlatko,

On Mon, Jul 22, 2013 at 06:48:52PM +0200, 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.

I should have remembered that you talked about this problem... Thanks
a lot for testing!

May I ask for the zone layout of your test machine(s)?  I.e. how many
nodes if NUMA, how big Normal and DMA32 (on Node 0) are.
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