linux-kernel - Re: [PATCH 5/8] mm: compaction: avoid overwork in migrate sync mode

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Message-ID: <4ECAC9C8.5040202@redhat.com>
Date:	Mon, 21 Nov 2011 16:59:36 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
CC:	linux-mm@...ck.org, Mel Gorman <mgorman@...e.de>,
	Minchan Kim <minchan.kim@...il.com>, Jan Kara <jack@...e.cz>,
	Andy Isaacson <adi@...apodia.org>,
	Johannes Weiner <jweiner@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/8] mm: compaction: avoid overwork in migrate sync mode

On 11/19/2011 02:54 PM, Andrea Arcangeli wrote:
> Add a lightweight sync migration (sync == 2) mode that avoids overwork
> so more suitable to be used by compaction to provide lower latency but

> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -552,7 +552,7 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
>   		nr_migrate = cc->nr_migratepages;
>   		err = migrate_pages(&cc->migratepages, compaction_alloc,
>   				(unsigned long)cc, false,
> -				cc->sync);
> +				cc->sync ? 2 : 0);

Great idea, but it would be good if these numbers got
a symbolic name so people trying to learn the code can
figure it out a little easier.

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