From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754095Ab1HLCsD (ORCPT ); Thu, 11 Aug 2011 22:48:03 -0400 Received: from mx1.redhat.com ([209.132.183.28]:18999 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753718Ab1HLCsB (ORCPT ); Thu, 11 Aug 2011 22:48:01 -0400 Message-ID: <4E449445.9000205@redhat.com> Date: Thu, 11 Aug 2011 22:47:33 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:5.0) Gecko/20110707 Thunderbird/5.0 MIME-Version: 1.0 To: Mel Gorman CC: Linux-MM , LKML , XFS , Dave Chinner , Christoph Hellwig , Johannes Weiner , Wu Fengguang , Jan Kara , Minchan Kim Subject: Re: [PATCH 6/7] mm: vmscan: Throttle reclaim if encountering too many dirty pages under writeback References: <1312973240-32576-1-git-send-email-mgorman@suse.de> <1312973240-32576-7-git-send-email-mgorman@suse.de> In-Reply-To: <1312973240-32576-7-git-send-email-mgorman@suse.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/10/2011 06:47 AM, Mel Gorman wrote: > Workloads that are allocating frequently and writing files place a > large number of dirty pages on the LRU. With use-once logic, it is > possible for them to reach the end of the LRU quickly requiring the > reclaimer to scan more to find clean pages. Ordinarily, processes that > are dirtying memory will get throttled by dirty balancing but this > is a global heuristic and does not take into account that LRUs are > maintained on a per-zone basis. This can lead to a situation whereby > reclaim is scanning heavily, skipping over a large number of pages > under writeback and recycling them around the LRU consuming CPU. > > This patch checks how many of the number of pages isolated from the > LRU were dirty and under writeback. If a percentage of them under > writeback, the process will be throttled if a backing device or the > zone is congested. Note that this applies whether it is anonymous or > file-backed pages that are under writeback meaning that swapping is > potentially throttled. This is intentional due to the fact if the > swap device is congested, scanning more pages and dispatching more > IO is not going to help matters. > > The percentage that must be in writeback depends on the priority. At > default priority, all of them must be dirty. At DEF_PRIORITY-1, 50% > of them must be, DEF_PRIORITY-2, 25% etc. i.e. as pressure increases > the greater the likelihood the process will get throttled to allow > the flusher threads to make some progress. > > Signed-off-by: Mel Gorman > Reviewed-by: Minchan Kim > Acked-by: Johannes Weiner Acked-by: Rik van Riel -- All rights reversed