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Date: Mon, 13 Feb 2017 10:49:40 +0000
From: Mel Gorman <mgorman@techsingularity.net>
Subject: Re: [PATCH v2 02/10] mm, compaction: remove redundant watermark
 check in compact_finished()
Message-ID: <20170213104940.jifpc5g5m5bty7cx@techsingularity.net>
References: <20170210172343.30283-1-vbabka@suse.cz>
 <20170210172343.30283-3-vbabka@suse.cz>
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In-Reply-To: <20170210172343.30283-3-vbabka@suse.cz>
Sender: owner-linux-mm@kvack.org
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To: Vlastimil Babka <vbabka@suse.cz>
Cc: linux-mm@kvack.org, Johannes Weiner <hannes@cmpxchg.org>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, David Rientjes <rientjes@google.com>, linux-kernel@vger.kernel.org, kernel-team@fb.com

On Fri, Feb 10, 2017 at 06:23:35PM +0100, Vlastimil Babka wrote:
> When detecting whether compaction has succeeded in forming a high-order page,
> __compact_finished() employs a watermark check, followed by an own search for
> a suitable page in the freelists. This is not ideal for two reasons:
> 
> - The watermark check also searches high-order freelists, but has a less strict
>   criteria wrt fallback. It's therefore redundant and waste of cycles. This was
>   different in the past when high-order watermark check attempted to apply
>   reserves to high-order pages.
> 
> - The watermark check might actually fail due to lack of order-0 pages.
>   Compaction can't help with that, so there's no point in continuing because of
>   that. It's possible that high-order page still exists and it terminates.
> 
> This patch therefore removes the watermark check. This should save some cycles
> and terminate compaction sooner in some cases.
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Acked-by: Mel Gorman <mgorman@techsingularity.net>

-- 
Mel Gorman
SUSE Labs

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