Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752661Ab1FYXSW (ORCPT ); Sat, 25 Jun 2011 19:18:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:26672 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752447Ab1FYXSS (ORCPT ); Sat, 25 Jun 2011 19:18:18 -0400 Message-ID: <4E066CA0.7060802@redhat.com> Date: Sat, 25 Jun 2011 19:17:52 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110428 Fedora/3.1.10-1.fc15 Lightning/1.0b3pre Thunderbird/3.1.10 MIME-Version: 1.0 To: Mel Gorman CC: Andrew Morton , =?UTF-8?B?UMOhZHJhaWcgQnJh?= =?UTF-8?B?ZHk=?= , James Bottomley , Colin King , Minchan Kim , Andrew Lutomirski , Johannes Weiner , linux-mm , linux-kernel Subject: Re: [PATCH 4/4] mm: vmscan: Only read new_classzone_idx from pgdat when reclaiming successfully References: <1308926697-22475-1-git-send-email-mgorman@suse.de> <1308926697-22475-5-git-send-email-mgorman@suse.de> In-Reply-To: <1308926697-22475-5-git-send-email-mgorman@suse.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2021 Lines: 41 On 06/24/2011 10:44 AM, Mel Gorman wrote: > During allocator-intensive workloads, kswapd will be woken frequently > causing free memory to oscillate between the high and min watermark. > This is expected behaviour. Unfortunately, if the highest zone is > small, a problem occurs. > > When balance_pgdat() returns, it may be at a lower classzone_idx than > it started because the highest zone was unreclaimable. Before checking > if it should go to sleep though, it checks pgdat->classzone_idx which > when there is no other activity will be MAX_NR_ZONES-1. It interprets > this as it has been woken up while reclaiming, skips scheduling and > reclaims again. As there is no useful reclaim work to do, it enters > into a loop of shrinking slab consuming loads of CPU until the highest > zone becomes reclaimable for a long period of time. > > There are two problems here. 1) If the returned classzone or order is > lower, it'll continue reclaiming without scheduling. 2) if the highest > zone was marked unreclaimable but balance_pgdat() returns immediately > at DEF_PRIORITY, the new lower classzone is not communicated back to > kswapd() for sleeping. > > This patch does two things that are related. If the end_zone is > unreclaimable, this information is communicated back. Second, if > the classzone or order was reduced due to failing to reclaim, new > information is not read from pgdat and instead an attempt is made to go > to sleep. Due to this, it is also necessary that pgdat->classzone_idx > be initialised each time to pgdat->nr_zones - 1 to avoid re-reads > being interpreted as wakeups. > > Reported-and-tested-by: Pádraig Brady > Signed-off-by: Mel Gorman Acked-by: Rik van Riel -- All rights reversed -- 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/