From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rik van Riel Subject: [PATCH 2/2] make the compaction "skip ahead" logic robust Date: Thu, 13 Sep 2012 15:48:24 -0400 Message-ID: <20120913154824.44cc0e28@cuia.bos.redhat.com> References: <20120822124032.GA12647@alpha.arachsys.com> <5034D437.8070106@redhat.com> <20120822144150.GA1400@alpha.arachsys.com> <5034F8F4.3080301@redhat.com> <20120825174550.GA8619@alpha.arachsys.com> <50391564.30401@redhat.com> <20120826105803.GA377@alpha.arachsys.com> <20120906092039.GA19234@alpha.arachsys.com> <20120912105659.GA23818@alpha.arachsys.com> <20120912122541.GO11266@suse.de> <20120912164615.GA14173@alpha.arachsys.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Mel Gorman , Avi Kivity , Shaohua Li , qemu-devel@nongnu.org, kvm@vger.kernel.org, linux-mm@kvack.org To: Richard Davies Return-path: Received: from mx1.redhat.com ([209.132.183.28]:37391 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755039Ab2IMTsc (ORCPT ); Thu, 13 Sep 2012 15:48:32 -0400 In-Reply-To: <20120912164615.GA14173@alpha.arachsys.com> Sender: kvm-owner@vger.kernel.org List-ID: Make the "skip ahead" logic in compaction resistant to compaction wrapping around to the end of the zone. This can lead to less efficient compaction when one thread has wrapped around to the end of the zone, and another simultaneous compactor has not done so yet. However, it should ensure that we do not suffer quadratic behaviour any more. Signed-off-by: Rik van Riel Reported-by: Richard Davies diff --git a/mm/compaction.c b/mm/compaction.c index 771775d..0656759 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -431,6 +431,24 @@ static bool suitable_migration_target(struct page *page) } /* + * We scan the zone in a circular fashion, starting at + * zone->compact_cached_free_pfn. Be careful not to skip if + * one compacting thread has just wrapped back to the end of the + * zone, but another thread has not. + */ +static bool compaction_may_skip(struct zone *zone, + struct compact_control *cc) +{ + if (!cc->wrapped && zone->compact_free_pfn < cc->start_pfn) + return true; + + if (cc->wrapped && zone_compact_free_pfn > cc->start_pfn) + return true; + + return false; +} + +/* * Based on information in the current compact_control, find blocks * suitable for isolating free pages from and then isolate them. */ @@ -471,13 +489,9 @@ static void isolate_freepages(struct zone *zone, /* * Skip ahead if another thread is compacting in the area - * simultaneously. If we wrapped around, we can only skip - * ahead if zone->compact_cached_free_pfn also wrapped to - * above our starting point. + * simultaneously, and has finished with this page block. */ - if (cc->order > 0 && (!cc->wrapped || - zone->compact_cached_free_pfn > - cc->start_free_pfn)) + if (cc->order > 0 && compaction_may_skip(zone, cc)) pfn = min(pfn, zone->compact_cached_free_pfn); if (!pfn_valid(pfn))