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Date: Wed, 27 Jun 2012 17:52:49 -0700 (PDT) From: David Rientjes <rientjes@...gle.com> To: Rik van Riel <riel@...hat.com> cc: Minchan Kim <minchan@...nel.org>, Jim Schutt <jaschut@...dia.gov>, Andrew Morton <akpm@...ux-foundation.org>, Mel Gorman <mel@....ul.ie>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, "ceph-devel@...r.kernel.org" <ceph-devel@...r.kernel.org> Subject: Re: excessive CPU utilization by isolate_freepages? On Wed, 27 Jun 2012, Rik van Riel wrote: > > I doubt compaction try to migrate continuously although we have no free > > memory. > > Could you apply this patch and retest? > > > > https://lkml.org/lkml/2012/6/21/30 > Not sure if Jim is using memcg; if not, then this won't be helpful. > Another possibility is that compaction is succeeding every time, > but since we always start scanning all the way at the beginning > and end of each zone, we waste a lot of CPU time rescanning the > same pages (that we just filled up with moved pages) to see if > any are free. > > In short, due to the way compaction behaves right now, > compaction + isolate_freepages are essentially quadratic. > > What we need to do is remember where we left off after a > successful compaction, so we can continue the search there > at the next invocation. > So when the free and migration scanners meet and compact_finished() == COMPACT_CONTINUE, loop around to the start of the zone and continue until you reach the pfn that it was started at? Seems appropriate. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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