From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx142.postini.com [74.125.245.142]) by kanga.kvack.org (Postfix) with SMTP id DFB516B0033 for ; Thu, 6 Jun 2013 08:51:04 -0400 (EDT) Message-ID: <51B085E5.9070103@parallels.com> Date: Thu, 6 Jun 2013 16:51:49 +0400 From: Glauber Costa MIME-Version: 1.0 Subject: Re: [PATCH v10 04/35] dentry: move to per-sb LRU locks References: <1370287804-3481-1-git-send-email-glommer@openvz.org> <1370287804-3481-5-git-send-email-glommer@openvz.org> <20130605160738.fe46654369044b6d94eadd1b@linux-foundation.org> <51B0424A.3090208@parallels.com> In-Reply-To: <51B0424A.3090208@parallels.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Glauber Costa , linux-fsdevel@vger.kernel.org, Mel Gorman , Dave Chinner , linux-mm@kvack.org, cgroups@vger.kernel.org, kamezawa.hiroyu@jp.fujitsu.com, Michal Hocko , Johannes Weiner , hughd@google.com, Greg Thelen , Dave Chinner On 06/06/2013 12:03 PM, Glauber Costa wrote: > On 06/06/2013 03:07 AM, Andrew Morton wrote: >> On Mon, 3 Jun 2013 23:29:33 +0400 Glauber Costa wrote: >> >>> From: Dave Chinner >>> >>> With the dentry LRUs being per-sb structures, there is no real need >>> for a global dentry_lru_lock. The locking can be made more >>> fine-grained by moving to a per-sb LRU lock, isolating the LRU >>> operations of different filesytsems completely from each other. >> >> What's the point to this patch? Is it to enable some additional >> development, or is it a standalone performance tweak? >> >> If the latter then the patch obviously makes this dentry code bloatier >> and straight-line slower. So we're assuming that the multiprocessor >> contention-avoidance benefits will outweigh that cost. Got any proof >> of this? >> >> > This is preparation for the whole point of this series, which is to > abstract the lru manipulation into a list_lru. It is hard to do that > when the dcache has a single lock for all manipulations, and multiple > lists under its umbrella. > > I have updated the Changelog, that now reads: With the dentry LRUs being per-sb structures, there is no real need for a global dentry_lru_lock. The locking can be made more fine-grained by moving to a per-sb LRU lock, isolating the LRU operations of different filesytsems completely from each other. The need for this is independent of any performance consideration that may arise: in the interest of abstracting the lru operations away, it is mandatory that each lru works around its own lock instead of a global lock for all of them. -- 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