linux-kernel - Re: [PATCH 07/17] mm: page_alloc: Take the ALLOC_NO

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Message-ID: <53691AF9.7080608@redhat.com>
Date:	Tue, 06 May 2014 13:25:13 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>, Linux-MM <linux-mm@...ck.org>,
	Linux-FSDevel <linux-fsdevel@...r.kernel.org>
CC:	Johannes Weiner <hannes@...xchg.org>,
	Vlastimil Babka <vbabka@...e.cz>, Jan Kara <jack@...e.cz>,
	Michal Hocko <mhocko@...e.cz>, Hugh Dickins <hughd@...gle.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 07/17] mm: page_alloc: Take the ALLOC_NO_WATERMARK check
 out of the fast path

On 05/01/2014 04:44 AM, Mel Gorman wrote:
> ALLOC_NO_WATERMARK is set in a few cases. Always by kswapd, always for
> __GFP_MEMALLOC, sometimes for swap-over-nfs, tasks etc. Each of these cases
> are relatively rare events but the ALLOC_NO_WATERMARK check is an unlikely
> branch in the fast path.  This patch moves the check out of the fast path
> and after it has been determined that the watermarks have not been met. This
> helps the common fast path at the cost of making the slow path slower and
> hitting kswapd with a performance cost. It's a reasonable tradeoff.
> 
> Signed-off-by: Mel Gorman <mgorman@...e.de>
> Acked-by: Johannes Weiner <hannes@...xchg.org>

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

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