linux-kernel - Re: [PATCH v2] mm: compaction: fix special case -1 order checks

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Message-ID: <20110602103820.GE7306@suse.de>
Date:	Thu, 2 Jun 2011 11:38:20 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mm: compaction: fix special case -1 order checks

On Mon, May 30, 2011 at 05:24:50PM +0200, Michal Hocko wrote:
> <SNIP>
> mm: compaction: fix special case -1 order checks
> 
> 56de7263 (mm: compaction: direct compact when a high-order allocation
> fails) introduced a check for cc->order == -1 in compact_finished. We
> should continue compacting in that case because the request came from
> userspace and there is no particular order to compact for.
> Similar check has been added by 82478fb7 (mm: compaction:
> prevent division-by-zero during user-requested compaction) for
> compaction_suitable.
> 
> The check is, however, done after zone_watermark_ok which uses order as
> a right hand argument for shifts. Not only watermark check is pointless
> if we can break out without it but it also uses 1 << -1 which is not
> well defined (at least from C standard). Let's move the -1 check above
> zone_watermark_ok.
> 
> [Minchan Kim <minchan.kim@...il.com> - caught compaction_suitable]
> Signed-off-by: Michal Hocko <mhocko@...e.cz>
> Cc: Mel Gorman <mgorman@...e.de>

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

-- 
Mel Gorman
SUSE Labs
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