linux-kernel - Re: [PATCH 1/7] mm: page_alloc: exclude unreclaimable allocations from zone fairness policy

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Message-ID: <52AB2BAD.4080003@redhat.com>
Date:	Fri, 13 Dec 2013 10:45:49 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave.hansen@...el.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/7] mm: page_alloc: exclude unreclaimable allocations
 from zone fairness policy

On 12/13/2013 09:10 AM, Mel Gorman wrote:
> From: Johannes Weiner <hannes@...xchg.org>
> 
> 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.
> 
> Cc: <stable@...nel.org>
> Bisected-by: Dave Hansen <dave.hansen@...el.com>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> Signed-off-by: Mel Gorman <mgorman@...e.de>

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

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