linux-kernel - Re: [PATCH] mm: Do not stall in synchronous compaction for THP allocations

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Message-ID: <20111115150139.GH27150@suse.de>
Date:	Tue, 15 Nov 2011 15:01:39 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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, linux-mm@...ck.org
Subject: Re: [PATCH] mm: Do not stall in synchronous compaction for THP
 allocations

On Tue, Nov 15, 2011 at 03:08:31AM +0100, Andrea Arcangeli wrote:
> On Tue, Nov 15, 2011 at 03:00:09AM +0100, Andrea Arcangeli wrote:
> > I didn't fill that gap but I was reading the code again and I don't
> > see why we keep retrying for -EAGAIN in the !sync case. Maybe the
> > below is good (untested). I doubt it's good to spend cpu to retry the
> > trylock or to retry the migrate on a pinned page by O_DIRECT. In fact
> > as far as THP success rate is concerned maybe we should "goto out"
> > instead of "goto fail" but I didn't change to that as compaction even
> > if it fails a subpage may still be successful at creating order
> > 1/2/3/4...8 pages. I only avoid 9 loops to retry a trylock or a page
> > under O_DIRECT. Maybe that will save a bit of CPU, I doubt it can
> > decrease the success rate in any significant way. I'll test it at the
> > next build...
> 
> At the same time also noticed another minor cleanup (also untested,
> will text at next build together with some other stuff).
> 
> ===
> From: Andrea Arcangeli <aarcange@...hat.com>
> Subject: [PATCH] compaction: move ISOLATE_CLEAN setting out of
>  compaction_migratepages loop
> 
> cc->sync and mode cannot change within the loop so move it out.
> 
> Signed-off-by: Andrea Arcangeli <aarcange@...hat.com>

Acked-by: Mel Gorman <mgorman@...e.de>

-- 
Mel Gorman
SUSE Labs
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