linux-kernel - Re: [PATCH v9] mm: compaction: handle incorrect MIGRATE

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Message-ID: <4FD5F405.9020904@redhat.com>
Date:	Mon, 11 Jun 2012 09:35:01 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Minchan Kim <minchan@...nel.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Hugh Dickins <hughd@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Dave Jones <davej@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Cong Wang <amwang@...hat.com>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>
Subject: Re: [PATCH v9] mm: compaction: handle incorrect MIGRATE_UNMOVABLE
 type pageblocks

On 06/11/2012 09:06 AM, Mel Gorman wrote:

> My initial support for this patch was based on an artifical load but one I
> felt was plausible to trigger if CMA was being used. In a normal workload
> I thought it might be possible to hit if a large process exited freeing
> a lot of pagetable pages from MIGRATE_UNMOVABLE blocks at the same time
> but that is a little unlikely and a test case would also look very artifical.
>
> Hence, I believe that if you require a real workload to demonstrate the
> benefit of the patch that it will be very difficult to find. The primary
> decision is if CMA needs this or not. I was under the impression that it
> was a help for CMA allocation success rates but I may be mistaken.

If it helps CMA allocation rates, it should also help
allocation rates for transparent hugepages.

Conveniently, THP allocation rates are already exported
in /proc/vmstat.  Now all we need is a test load :)

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