linux-kernel - Re: [RFC PATCH 0/4] Configurable fair allocation zone policy

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Date:	Thu, 12 Dec 2013 15:34:22 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave.hansen@...el.com>,
	Rik van Riel <riel@...hat.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/4] Configurable fair allocation zone policy

On Thu, Dec 12, 2013 at 03:06:15PM +0000, Mel Gorman wrote:
> Commit 81c0a2bb ("mm: page_alloc: fair zone allocator policy") solved a
> bug whereby new pages could be reclaimed before old pages because of how
> the page allocator and kswapd interacted on the per-zone LRU lists.
> 
> Unfortunately a side-effect missed during review was that it's now very
> easy to allocate remote memory on NUMA machines. The problem is that
> it is not a simple case of just restoring local allocation policies as
> there are genuine reasons why global page aging may be prefereable. It's
> still a major change to default behaviour so this patch makes the policy
> configurable and sets what I think is a sensible default.
> 
> The patches are on top of some NUMA balancing patches currently in -mm.
> The first patch in the series is a patch posted by Johannes that must be
> taken into account before any of my patches on top. The last patch of the
> series is what alters default behaviour and makes the fair zone allocator
> policy configurable.
> 
> Sniff test results based on following kernels
> 
> vanilla		 3.13-rc3 stock
> instrument-v5r1  NUMA balancing patches just to rule out any conflicts there
> lruslabonly-v1r2 Patch 1 only
> local-v1r2	 Full series
> 

These figures need to be redone. The instrument-v5r1 and later kernels
included a debugging patch that increases migration rates to trigger
another bug. The figures of local-v1r2 relative to instrument-v5r1 are
fine but not relative to 3.13.0-rc3-vanilla

-- 
Mel Gorman
SUSE Labs
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