From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752451AbZI0T4R (ORCPT ); Sun, 27 Sep 2009 15:56:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751610AbZI0T4Q (ORCPT ); Sun, 27 Sep 2009 15:56:16 -0400 Received: from cantor.suse.de ([195.135.220.2]:38438 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751107AbZI0T4Q (ORCPT ); Sun, 27 Sep 2009 15:56:16 -0400 Date: Sun, 27 Sep 2009 21:56:19 +0200 From: Nick Piggin To: Al Viro Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [patch 04/33] fs: brlock vfsmount_lock Message-ID: <20090927195619.GG6327@wotan.suse.de> References: <20090904065142.114706411@nick.local0.net> <20090904065534.447753909@nick.local0.net> <20090922151751.GM5858@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090922151751.GM5858@ZenIV.linux.org.uk> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 22, 2009 at 04:17:51PM +0100, Al Viro wrote: > On Fri, Sep 04, 2009 at 04:51:45PM +1000, npiggin@suse.de wrote: > > Use a brlock for the vfsmount lock. > > I like it, but I'd like to see how costly it becomes on heavily SMP boxen. > Creation/removal of bindings as load... I could test that... Is there some realistic scenario I can try to implement that exercises this? (failing that, I'll happily do a microbenchmark). I was thinking it *might* be possible to do RCU... but especially coming up with a scheme that avoids synchronize_rcu() in the umount path is not trivial, so perhaps the simple read/write annotations with brlock behind the scenes is a more reasonable step. I do also actually owe you some documentation with this one too, which I will get around to adding.