linux-kernel - Re: [PATCH] mm: fix special case -1 order check in compact

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Message-Id: <20110531133430.d91aa49d.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 31 May 2011 13:34:30 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: fix special case -1 order check in compact_finished

On Mon, 30 May 2011 14:38:31 +0200
Michal Hocko <mhocko@...e.cz> wrote:

> 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.
> 
> 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.
> 
> Signed-off-by: Michal Hocko <mhocko@...e.cz>
> Cc: Mel Gorman <mgorman@...e.de>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hioryu@...fujitsu.com>


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