From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx196.postini.com [74.125.245.196]) by kanga.kvack.org (Postfix) with SMTP id 086886B006C for ; Thu, 20 Sep 2012 14:54:24 -0400 (EDT) Message-ID: <505B6658.1080706@redhat.com> Date: Thu, 20 Sep 2012 14:54:16 -0400 From: Rik van Riel MIME-Version: 1.0 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: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Richard Davies , Shaohua Li , Avi Kivity , QEMU-devel , KVM , Linux-MM , LKML 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org