From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx201.postini.com [74.125.245.201]) by kanga.kvack.org (Postfix) with SMTP id 1419C6B00AB for ; Wed, 14 Nov 2012 16:44:21 -0500 (EST) Date: Wed, 14 Nov 2012 22:43:40 +0100 From: Johannes Hirte Subject: Re: [PATCH] Revert "mm: vmscan: scale number of pages reclaimed by reclaim/compaction based on failures" Message-ID: <20121114224340.5f7cee78@fem.tu-ilmenau.de> In-Reply-To: <20121109083637.GD8218@suse.de> References: <5077434D.7080008@suse.cz> <50780F26.7070007@suse.cz> <20121012135726.GY29125@suse.de> <507BDD45.1070705@suse.cz> <20121015110937.GE29125@suse.de> <5093A3F4.8090108@redhat.com> <5093A631.5020209@suse.cz> <509422C3.1000803@suse.cz> <20121105142449.GI8218@suse.de> <20121106111554.1896c3f3@fem.tu-ilmenau.de> <20121109083637.GD8218@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Andrew Morton , Zdenek Kabelac , Valdis.Kletnieks@vt.edu, Jiri Slaby , linux-mm@kvack.org, Rik van Riel , Jiri Slaby , LKML Am Fri, 9 Nov 2012 08:36:37 +0000 schrieb Mel Gorman : > On Tue, Nov 06, 2012 at 11:15:54AM +0100, Johannes Hirte wrote: > > Am Mon, 5 Nov 2012 14:24:49 +0000 > > schrieb Mel Gorman : > > > > > Jiri Slaby reported the following: > > > > > > (It's an effective revert of "mm: vmscan: scale number of > > > pages reclaimed by reclaim/compaction based on failures".) Given > > > kswapd had hours of runtime in ps/top output yesterday in the > > > morning and after the revert it's now 2 minutes in sum for the > > > last 24h, I would say, it's gone. > > > > > > The intention of the patch in question was to compensate for the > > > loss of lumpy reclaim. Part of the reason lumpy reclaim worked is > > > because it aggressively reclaimed pages and this patch was meant > > > to be a sane compromise. > > > > > > When compaction fails, it gets deferred and both compaction and > > > reclaim/compaction is deferred avoid excessive reclaim. However, > > > since commit c6543459 (mm: remove __GFP_NO_KSWAPD), kswapd is > > > woken up each time and continues reclaiming which was not taken > > > into account when the patch was developed. > > > > > > Attempts to address the problem ended up just changing the shape > > > of the problem instead of fixing it. The release window gets > > > closer and while a THP allocation failing is not a major problem, > > > kswapd chewing up a lot of CPU is. This patch reverts "mm: > > > vmscan: scale number of pages reclaimed by reclaim/compaction > > > based on failures" and will be revisited in the future. > > > > > > Signed-off-by: Mel Gorman > > > --- > > > mm/vmscan.c | 25 ------------------------- > > > 1 file changed, 25 deletions(-) > > > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > > index 2624edc..e081ee8 100644 > > > --- a/mm/vmscan.c > > > +++ b/mm/vmscan.c > > > @@ -1760,28 +1760,6 @@ static bool in_reclaim_compaction(struct > > > scan_control *sc) return false; > > > } > > > > > > -#ifdef CONFIG_COMPACTION > > > -/* > > > - * If compaction is deferred for sc->order then scale the number > > > of pages > > > - * reclaimed based on the number of consecutive allocation > > > failures > > > - */ > > > -static unsigned long scale_for_compaction(unsigned long > > > pages_for_compaction, > > > - struct lruvec *lruvec, struct > > > scan_control *sc) -{ > > > - struct zone *zone = lruvec_zone(lruvec); > > > - > > > - if (zone->compact_order_failed <= sc->order) > > > - pages_for_compaction <<= > > > zone->compact_defer_shift; > > > - return pages_for_compaction; > > > -} > > > -#else > > > -static unsigned long scale_for_compaction(unsigned long > > > pages_for_compaction, > > > - struct lruvec *lruvec, struct > > > scan_control *sc) -{ > > > - return pages_for_compaction; > > > -} > > > -#endif > > > - > > > /* > > > * Reclaim/compaction is used for high-order allocation > > > requests. It reclaims > > > * order-0 pages before compacting the zone. > > > should_continue_reclaim() returns @@ -1829,9 +1807,6 @@ static > > > inline bool should_continue_reclaim(struct lruvec *lruvec, > > > * inactive lists are large enough, continue reclaiming > > > */ > > > pages_for_compaction = (2UL << sc->order); > > > - > > > - pages_for_compaction = > > > scale_for_compaction(pages_for_compaction, > > > - lruvec, sc); > > > inactive_lru_pages = get_lru_size(lruvec, > > > LRU_INACTIVE_FILE); if (nr_swap_pages > 0) > > > inactive_lru_pages += get_lru_size(lruvec, > > > LRU_INACTIVE_ANON); -- > > > > Even with this patch I see kswapd0 very often on top. Much more than > > with kernel 3.6. > > How severe is the CPU usage? The higher usage can be explained by "mm: > remove __GFP_NO_KSWAPD" which allows kswapd to compact memory to > reduce the amount of time processes spend in compaction but will > result in the CPU cost being incurred by kswapd. > > Is it really high like the bug was reporting with high usage over long > periods of time or do you just see it using 2-6% of CPU for short > periods? It is really high. I've seen with compile-jobs (make -j4 on dual core) kswapd0 consuming at least 50% CPU most time. -- 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/ . Don't email: email@kvack.org