From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756023Ab2ITS6n (ORCPT ); Thu, 20 Sep 2012 14:58:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45909 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755310Ab2ITSya (ORCPT ); Thu, 20 Sep 2012 14:54:30 -0400 Message-ID: <505B6658.1080706@redhat.com> Date: Thu, 20 Sep 2012 14:54:16 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: Mel Gorman CC: Richard Davies , Shaohua Li , Avi Kivity , QEMU-devel , KVM , Linux-MM , LKML Subject: Re: [PATCH 2/6] mm: compaction: Acquire the zone->lru_lock as late as possible References: <1348149875-29678-1-git-send-email-mgorman@suse.de> <1348149875-29678-3-git-send-email-mgorman@suse.de> In-Reply-To: <1348149875-29678-3-git-send-email-mgorman@suse.de> 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 09/20/2012 10:04 AM, Mel Gorman wrote: > Compactions migrate scanner acquires the zone->lru_lock when scanning a range > of pages looking for LRU pages to acquire. It does this even if there are > no LRU pages in the range. If multiple processes are compacting then this > can cause severe locking contention. To make matters worse commit b2eef8c0 > (mm: compaction: minimise the time IRQs are disabled while isolating pages > for migration) releases the lru_lock every SWAP_CLUSTER_MAX pages that are > scanned. > > This patch makes two changes to how the migrate scanner acquires the LRU > lock. First, it only releases the LRU lock every SWAP_CLUSTER_MAX pages if > the lock is contended. This reduces the number of times it unnecessarily > disables and re-enables IRQs. The second is that it defers acquiring the > LRU lock for as long as possible. If there are no LRU pages or the only > LRU pages are transhuge then the LRU lock will not be acquired at all > which reduces contention on zone->lru_lock. > > Signed-off-by: Mel Gorman Acked-by: Rik van Riel