From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752598Ab3DLC42 (ORCPT ); Thu, 11 Apr 2013 22:56:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42107 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751367Ab3DLC41 (ORCPT ); Thu, 11 Apr 2013 22:56:27 -0400 Message-ID: <51677779.8000506@redhat.com> Date: Thu, 11 Apr 2013 22:54:49 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 MIME-Version: 1.0 To: Mel Gorman CC: Andrew Morton , Jiri Slaby , Valdis Kletnieks , Zlatko Calusic , Johannes Weiner , dormando , Satoru Moriya , Michal Hocko , Linux-MM , LKML Subject: Re: [PATCH 07/10] mm: vmscan: Block kswapd if it is encountering pages under writeback References: <1365505625-9460-1-git-send-email-mgorman@suse.de> <1365505625-9460-8-git-send-email-mgorman@suse.de> In-Reply-To: <1365505625-9460-8-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 04/09/2013 07:07 AM, Mel Gorman wrote: > Historically, kswapd used to congestion_wait() at higher priorities if it > was not making forward progress. This made no sense as the failure to make > progress could be completely independent of IO. It was later replaced by > wait_iff_congested() and removed entirely by commit 258401a6 (mm: don't > wait on congested zones in balance_pgdat()) as it was duplicating logic > in shrink_inactive_list(). > > This is problematic. If kswapd encounters many pages under writeback and > it continues to scan until it reaches the high watermark then it will > quickly skip over the pages under writeback and reclaim clean young > pages or push applications out to swap. > > The use of wait_iff_congested() is not suited to kswapd as it will only > stall if the underlying BDI is really congested or a direct reclaimer was > unable to write to the underlying BDI. kswapd bypasses the BDI congestion > as it sets PF_SWAPWRITE but even if this was taken into account then it > would cause direct reclaimers to stall on writeback which is not desirable. > > This patch sets a ZONE_WRITEBACK flag if direct reclaim or kswapd is > encountering too many pages under writeback. If this flag is set and > kswapd encounters a PageReclaim page under writeback then it'll assume > that the LRU lists are being recycled too quickly before IO can complete > and block waiting for some IO to complete. > > Signed-off-by: Mel Gorman > Reviewed-by: Michal Hocko Acked-by: Rik van Riel -- All rights reversed