From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932680Ab2IURva (ORCPT ); Fri, 21 Sep 2012 13:51:30 -0400 Received: from mx1.redhat.com ([209.132.183.28]:10382 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932208Ab2IURv2 (ORCPT ); Fri, 21 Sep 2012 13:51:28 -0400 Date: Fri, 21 Sep 2012 14:51:15 -0300 From: Rafael Aquini To: Mel Gorman Cc: Andrew Morton , Richard Davies , Shaohua Li , Rik van Riel , Avi Kivity , QEMU-devel , KVM , Linux-MM , LKML Subject: Re: [PATCH 5/9] mm: compaction: Acquire the zone->lru_lock as late as possible Message-ID: <20120921175115.GE6665@optiplex.redhat.com> References: <1348224383-1499-1-git-send-email-mgorman@suse.de> <1348224383-1499-6-git-send-email-mgorman@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1348224383-1499-6-git-send-email-mgorman@suse.de> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 21, 2012 at 11:46:19AM +0100, 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 > --- Acked-by: Rafael Aquini