linux-kernel - Re: [patch] mm, compaction: abort free scanner if split fails

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Date:	Wed, 22 Jun 2016 13:02:30 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan@...nel.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Mel Gorman <mgorman@...hsingularity.net>,
	Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, stable@...r.kernel.org
Subject: Re: [patch] mm, compaction: abort free scanner if split fails

On 06/22/2016 03:22 AM, David Rientjes wrote:
> If the memory compaction free scanner cannot successfully split a free
> page (only possible due to per-zone low watermark), terminate the free
> scanner rather than continuing to scan memory needlessly.  If the
> watermark is insufficient for a free page of order <= cc->order, then
> terminate the scanner since all future splits will also likely fail.
>
> This prevents the compaction freeing scanner from scanning all memory on
> very large zones (very noticeable for zones > 128GB, for instance) when
> all splits will likely fail while holding zone->lock.
>
> Cc: stable@...r.kernel.org
> Signed-off-by: David Rientjes <rientjes@...gle.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  Based on Linus's tree
>
>  Suggest including in 4.7 if anybody else agrees?

4.7 definitely. Stable is less clear especially if you say it won't apply 
cleanly, but if you're ready to handle it, sure. The rules now allow fixing 
glaring performance bugs.

Thanks.