From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx120.postini.com [74.125.245.120]) by kanga.kvack.org (Postfix) with SMTP id C09596B005A for ; Fri, 29 Jun 2012 06:03:07 -0400 (EDT) Date: Fri, 29 Jun 2012 11:02:58 +0100 From: Mel Gorman Subject: Re: [PATCH -mm v2] mm: have order > 0 compaction start off where it left Message-ID: <20120629100258.GA13141@csn.ul.ie> References: <20120628135520.0c48b066@annuminas.surriel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20120628135520.0c48b066@annuminas.surriel.com> Sender: owner-linux-mm@kvack.org List-ID: To: Rik van Riel Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , jaschut@sandia.gov, minchan@kernel.org, kamezawa.hiroyu@jp.fujitsu.com On Thu, Jun 28, 2012 at 01:55:20PM -0400, Rik van Riel wrote: > Order > 0 compaction stops when enough free pages of the correct > page order have been coalesced. When doing subsequent higher order > allocations, it is possible for compaction to be invoked many times. > > However, the compaction code always starts out looking for things to > compact at the start of the zone, and for free pages to compact things > to at the end of the zone. > > This can cause quadratic behaviour, with isolate_freepages starting > at the end of the zone each time, even though previous invocations > of the compaction code already filled up all free memory on that end > of the zone. > > This can cause isolate_freepages to take enormous amounts of CPU > with certain workloads on larger memory systems. > > The obvious solution is to have isolate_freepages remember where > it left off last time, and continue at that point the next time > it gets invoked for an order > 0 compaction. This could cause > compaction to fail if cc->free_pfn and cc->migrate_pfn are close > together initially, in that case we restart from the end of the > zone and try once more. > > Forced full (order == -1) compactions are left alone. > > Cc: Andrew Morton > Cc: Mel Gorman > Reported-by: Jim Schutt > Signed-off-by: Rik van Riel > --- > v2: implement Mel's suggestions, handling wrap-around etc > I have not tested it myself but it looks correct! Thanks very much. Acked-by: Mel Gorman -- Mel Gorman SUSE Labs -- 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