Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752554AbaJTP1T (ORCPT ); Mon, 20 Oct 2014 11:27:19 -0400 Received: from mx1.redhat.com ([209.132.183.28]:27545 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751272AbaJTP1S (ORCPT ); Mon, 20 Oct 2014 11:27:18 -0400 Message-ID: <544529C0.5080205@redhat.com> Date: Mon, 20 Oct 2014 11:26:56 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.7.0 MIME-Version: 1.0 To: Vlastimil Babka , Andrew Morton CC: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Minchan Kim , Mel Gorman , Joonsoo Kim , Michal Nazarewicz , Naoya Horiguchi , Christoph Lameter , David Rientjes Subject: Re: [PATCH 4/5] mm, compaction: always update cached scanner positions References: <1412696019-21761-1-git-send-email-vbabka@suse.cz> <1412696019-21761-5-git-send-email-vbabka@suse.cz> In-Reply-To: <1412696019-21761-5-git-send-email-vbabka@suse.cz> 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 10/07/2014 11:33 AM, Vlastimil Babka wrote: > Compaction caches the migration and free scanner positions between compaction > invocations, so that the whole zone gets eventually scanned and there is no > bias towards the initial scanner positions at the beginning/end of the zone. > > The cached positions are continuously updated as scanners progress and the > updating stops as soon as a page is successfully isolated. The reasoning > behind this is that a pageblock where isolation succeeded is likely to succeed > again in near future and it should be worth revisiting it. > > However, the downside is that potentially many pages are rescanned without > successful isolation. At worst, there might be a page where isolation from LRU > succeeds but migration fails (potentially always). So upon encountering this > page, cached position would always stop being updated for no good reason. > It might have been useful to let such page be rescanned with sync compaction > after async one failed, but this is now handled by caching scanner position > for async and sync mode separately since commit 35979ef33931 ("mm, compaction: > add per-zone migration pfn cache for async compaction"). > > After this patch, cached positions are updated unconditionally. In > stress-highalloc benchmark, this has decreased the numbers of scanned pages > by few percent, without affecting allocation success rates. > > Signed-off-by: Vlastimil Babka > Cc: Minchan Kim > Cc: Mel Gorman > Cc: Joonsoo Kim > Cc: Michal Nazarewicz > Cc: Naoya Horiguchi > Cc: Christoph Lameter > Cc: Rik van Riel > Cc: David Rientjes Acked-by: Rik van Riel -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/