From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752863AbaELJJb (ORCPT ); Mon, 12 May 2014 05:09:31 -0400 Received: from cantor2.suse.de ([195.135.220.15]:52269 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751015AbaELJJ3 (ORCPT ); Mon, 12 May 2014 05:09:29 -0400 Message-ID: <53708FC5.4000100@suse.cz> Date: Mon, 12 May 2014 11:09:25 +0200 From: Vlastimil Babka User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: Joonsoo Kim CC: Andrew Morton , David Rientjes , Hugh Dickins , Greg Thelen , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Minchan Kim , Mel Gorman , Bartlomiej Zolnierkiewicz , Michal Nazarewicz , Naoya Horiguchi , Christoph Lameter , Rik van Riel Subject: Re: [PATCH v2 2/2] mm/compaction: avoid rescanning pageblocks in isolate_freepages References: <1399464550-26447-1-git-send-email-vbabka@suse.cz> <1399464550-26447-2-git-send-email-vbabka@suse.cz> <20140508052845.GB9161@js1304-P5Q-DELUXE> In-Reply-To: <20140508052845.GB9161@js1304-P5Q-DELUXE> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/08/2014 07:28 AM, Joonsoo Kim wrote: > On Wed, May 07, 2014 at 02:09:10PM +0200, Vlastimil Babka wrote: >> The compaction free scanner in isolate_freepages() currently remembers PFN of >> the highest pageblock where it successfully isolates, to be used as the >> starting pageblock for the next invocation. The rationale behind this is that >> page migration might return free pages to the allocator when migration fails >> and we don't want to skip them if the compaction continues. >> >> Since migration now returns free pages back to compaction code where they can >> be reused, this is no longer a concern. This patch changes isolate_freepages() >> so that the PFN for restarting is updated with each pageblock where isolation >> is attempted. Using stress-highalloc from mmtests, this resulted in 10% >> reduction of the pages scanned by the free scanner. > > Hello, > > Although this patch could reduce page scanned, it is possible to skip > scanning fresh pageblock. If there is zone lock contention and we are on > asyn compaction, we stop scanning this pageblock immediately. And > then, we will continue to scan next pageblock. With this patch, > next_free_pfn is updated in this case, so we never come back again to this > pageblock. Possibly this makes compaction success rate low, doesn't > it? Hm, you're right and thanks for catching that, but I think this is a sign of a worse and older issue than skipping a pageblock? When isolate_freepages_block() breaks loop due to lock contention, then isolate_freepages() (which called it) should also immediately quit its loop. Trying another pageblock in the same zone with the same zone->lock makes no sense here? If this is fixed, then the issue you're pointing out will also be fixed as next_free_pfn will still point to the pageblock where the break occured. > Thanks. >