linux-kernel - Re: [PATCH] mm/compaction: restore COMPACT_CLUSTER

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Message-ID: <20151208094546.GD19677@suse.de>
Date:	Tue, 8 Dec 2015 09:45:46 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Joonsoo Kim <js1304@...il.com>, Vlastimil Babka <vbabka@...e.cz>,
	David Rientjes <rientjes@...gle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH] mm/compaction: restore COMPACT_CLUSTER_MAX to 32

On Mon, Dec 07, 2015 at 05:00:41PM -0800, Andrew Morton wrote:
> On Thu,  3 Dec 2015 13:11:40 +0900 Joonsoo Kim <js1304@...il.com> wrote:
> 
> > Until now, COMPACT_CLUSTER_MAX is defined as SWAP_CLUSTER_MAX.
> > Commit ("mm: increase SWAP_CLUSTER_MAX to batch TLB flushes")
> > changes SWAP_CLUSTER_MAX from 32 to 256 to improve tlb flush performance
> > so COMPACT_CLUSTER_MAX is also changed to 256.
> 
> "mm: increase SWAP_CLUSTER_MAX to batch TLB flushes" has been in limbo
> for quite a while.  Because it has been unclear whether the patch's
> benefits exceed its costs+risks.
> 
> We should make a decision here - either do the appropriate testing or
> drop the patch.
> 

At this point, drop it. The benefits that apply to some corner cases are
marginal but the concerns about potentially isolating and reclaiming too
much persist.

-- 
Mel Gorman
SUSE Labs
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