From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id 4A66C8D0039 for ; Wed, 9 Feb 2011 23:04:53 -0500 (EST) Received: by iwc10 with SMTP id 10so881448iwc.14 for ; Wed, 09 Feb 2011 20:04:51 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20110209154606.GJ27110@cmpxchg.org> References: <20110209154606.GJ27110@cmpxchg.org> Date: Thu, 10 Feb 2011 13:04:51 +0900 Message-ID: Subject: Re: [patch] vmscan: fix zone shrinking exit when scan work is done From: Minchan Kim Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Andrew Morton , Andrea Arcangeli , Mel Gorman , Rik van Riel , Michal Hocko , Kent Overstreet , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu, Feb 10, 2011 at 12:46 AM, Johannes Weiner wrot= e: > Hi, > > I think this should fix the problem of processes getting stuck in > reclaim that has been reported several times. =C2=A0Kent actually > single-stepped through this code and noted that it was never exiting > shrink_zone(), which really narrowed it down a lot, considering the > tons of nested loops from the allocator down to the list shrinking. > > =C2=A0 =C2=A0 =C2=A0 =C2=A0Hannes > > --- > From: Johannes Weiner > Subject: vmscan: fix zone shrinking exit when scan work is done > > '3e7d344 mm: vmscan: reclaim order-0 and use compaction instead of > lumpy reclaim' introduced an indefinite loop in shrink_zone(). > > It meant to break out of this loop when no pages had been reclaimed > and not a single page was even scanned. =C2=A0The way it would detect the > latter is by taking a snapshot of sc->nr_scanned at the beginning of > the function and comparing it against the new sc->nr_scanned after the > scan loop. =C2=A0But it would re-iterate without updating that snapshot, > looping forever if sc->nr_scanned changed at least once since > shrink_zone() was invoked. > > This is not the sole condition that would exit that loop, but it > requires other processes to change the zone state, as the reclaimer > that is stuck obviously can not anymore. > > This is only happening for higher-order allocations, where reclaim is > run back to back with compaction. > > Reported-by: Michal Hocko > Reported-by: Kent Overstreet > Signed-off-by: Johannes Weiner Reviewed-by: Minchan Kim --=20 Kind regards, Minchan Kim -- 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 internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org