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

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Message-ID: <20120611130612.GA3030@suse.de>
Date:	Mon, 11 Jun 2012 14:06:12 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Minchan Kim <minchan@...nel.org>
Cc:	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>,
	Rik van Riel <riel@...hat.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 Tue, Jun 05, 2012 at 03:05:40PM +0900, Minchan Kim wrote:
> > Let's throw it away until the author send us data.
> > 
> 
> I guess it's hard to make such workload to prove it's useful normally.
> But we can't make sure there isn't such workload in the world.
> So I hope listen VOC. At least, Mel might require it.
> 

I'm playing a lot of catch-up at the moment after being out for a few days
so sorry for my silence on this and other threads.

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.

-- 
Mel Gorman
SUSE Labs
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