linux-kernel - Re: [PATCH 2/2] mm: support MIGRATE

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Date:	Wed, 5 Sep 2012 11:56:11 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 2/2] mm: support MIGRATE_DISCARD

On Wed, Sep 05, 2012 at 05:11:13PM +0900, Minchan Kim wrote:
> This patch introudes MIGRATE_DISCARD mode in migration.
> It drops *clean cache pages* instead of migration so that
> migration latency could be reduced by avoiding (memcpy + page remapping).
> It's useful for CMA because latency of migration is very important rather
> than eviction of background processes's workingset. In addition, it needs
> less free pages for migration targets so it could avoid memory reclaiming
> to get free pages, which is another factor increase latency.
> 

Bah, this was released while I was reviewing the older version. I did
not read this one as closely but I see the enum problems have gone away
at least. I'd still prefer if CMA had an additional helper to discard
some pages with shrink_page_list() and migrate the remaining pages with
migrate_pages(). That would remove the need to add a MIGRATE_DISCARD
migrate mode at all.

-- 
Mel Gorman
SUSE Labs
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