From mboxrd@z Thu Jan 1 00:00:00 1970 From: Glauber Costa Subject: Re: [PATCH v10 04/35] dentry: move to per-sb LRU locks Date: Thu, 6 Jun 2013 16:51:49 +0400 Message-ID: <51B085E5.9070103@parallels.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Cc: Glauber Costa , , Mel Gorman , Dave Chinner , , , , Michal Hocko , Johannes Weiner , , Greg Thelen , Dave Chinner To: Andrew Morton Return-path: In-Reply-To: <51B0424A.3090208@parallels.com> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org 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