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

From: Mel Gorman
Date: Thu Jun 02 2011 - 06:38:28 EST

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 <> - caught compaction_suitable]
> Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>

Acked-by: Mel Gorman <mgorman@xxxxxxx>

Mel Gorman
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