linux-kernel - Re: [patch] mm: page_alloc: exclude unreclaimable allocations from zone fairness policy

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Message-ID: <52A8ADE4.8020609@redhat.com>
Date:	Wed, 11 Dec 2013 13:24:36 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Johannes Weiner <hannes@...xchg.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave.hansen@...el.com>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] mm: page_alloc: exclude unreclaimable allocations from
 zone fairness policy

On 12/11/2013 01:09 PM, Johannes Weiner wrote:
> Dave Hansen noted a regression in a microbenchmark that loops around
> open() and close() on an 8-node NUMA machine and bisected it down to
> 81c0a2bb515f ("mm: page_alloc: fair zone allocator policy").  That
> change forces the slab allocations of the file descriptor to spread
> out to all 8 nodes, causing remote references in the page allocator
> and slab.
> 
> The round-robin policy is only there to provide fairness among memory
> allocations that are reclaimed involuntarily based on pressure in each
> zone.  It does not make sense to apply it to unreclaimable kernel
> allocations that are freed manually, in this case instantly after the
> allocation, and incur the remote reference costs twice for no reason.
> 
> Only round-robin allocations that are usually freed through page
> reclaim or slab shrinking.
> 
> Bisected-by: Dave Hansen <dave.hansen@...el.com>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> Cc: <stable@...nel.org>

Reviewed-by: Rik van Riel <riel@...hat.com>


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