From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with ESMTP id F073E8D003A for ; Tue, 18 Jan 2011 12:22:36 -0500 (EST) Date: Tue, 18 Jan 2011 17:21:09 +0000 From: Mel Gorman Subject: Re: [patch] mm: compaction: prevent division-by-zero during user-requested compaction Message-ID: <20110118172109.GA18984@csn.ul.ie> References: <1295370412-2645-1-git-send-email-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <1295370412-2645-1-git-send-email-hannes@cmpxchg.org> Sender: owner-linux-mm@kvack.org To: Johannes Weiner Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Tue, Jan 18, 2011 at 06:06:52PM +0100, Johannes Weiner wrote: > Up until '3e7d344 mm: vmscan: reclaim order-0 and use compaction > instead of lumpy reclaim', compaction skipped calculating the > fragmentation index of a zone when compaction was explicitely > requested through the procfs knob. > > However, when compaction_suitable was introduced, it did not come with > an extra check for order == -1, set on explicit compaction requests, > and passed this order on to the fragmentation index calculation, where > it overshifts the number of requested pages, leading to a division by > zero. > > This patch makes sure that order == -1 is recognized as the flag it is > rather than passing it along as valid order parameter. > > Signed-off-by: Johannes Weiner It could do with a comment saying that order == -1 is expected when compacting via /proc/sys/vm/compact_memory but otherwise; Reviewed-by: Mel Gorman > --- > mm/compaction.c | 3 +++ > 1 files changed, 3 insertions(+), 0 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 6d592a0..114c145 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -453,6 +453,9 @@ unsigned long compaction_suitable(struct zone *zone, int order) > if (!zone_watermark_ok(zone, 0, watermark, 0, 0)) > return COMPACT_SKIPPED; > > + if (order == -1) > + return COMPACT_CONTINUE; > + > /* > * fragmentation index determines if allocation failures are due to > * low memory or external fragmentation > -- > 1.7.3.4 > -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org