From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH] vfs: Speed up deactivate_super for non-modular
 filesystems
Date: Mon, 7 May 2012 16:56:47 -0700
Message-ID: <20120507235647.GH21152@linux.vnet.ibm.com>
References: <m1vckcdoey.fsf@fess.ebiederm.org>
 <1336142995.25479.49.camel@marge.simpson.net>
 <m1zk9oc61j.fsf@fess.ebiederm.org>
 <1336150643.7502.4.camel@marge.simpson.net>
 <m1fwbfd71h.fsf@fess.ebiederm.org>
 <1336197362.7346.9.camel@marge.simpson.net>
 <1336198093.7346.11.camel@marge.simpson.net>
 <1336201977.7346.22.camel@marge.simpson.net>
 <87r4uv64oj.fsf_-_@xmission.com>
 <20120507221706.GI22082@ZenIV.linux.org.uk>
Reply-To: paulmck@linux.vnet.ibm.com
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Oleg Nesterov <oleg@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Pavel Emelyanov <xemul@parallels.com>,
	Cyrill Gorcunov <gorcunov@openvz.org>,
	Louis Rilling <louis.rilling@kerlabs.com>,
	Mike Galbraith <efault@gmx.de>,
	Christoph Hellwig <hch@infradead.org>,
	linux-fsdevel@vger.kernel.org
To: Al Viro <viro@ZenIV.linux.org.uk>
Return-path: <linux-fsdevel-owner@vger.kernel.org>
Received: from e35.co.us.ibm.com ([32.97.110.153]:35847 "EHLO
	e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1756665Ab2EGX5s (ORCPT
	<rfc822;linux-fsdevel@vger.kernel.org>);
	Mon, 7 May 2012 19:57:48 -0400
Received: from /spool/local
	by e35.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted
	for <linux-fsdevel@vger.kernel.org> from <paulmck@linux.vnet.ibm.com>;
	Mon, 7 May 2012 17:57:44 -0600
Content-Disposition: inline
In-Reply-To: <20120507221706.GI22082@ZenIV.linux.org.uk>
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>

On Mon, May 07, 2012 at 11:17:06PM +0100, Al Viro wrote:
> On Mon, May 07, 2012 at 02:51:08PM -0700, Eric W. Biederman wrote:
> 
> > /proc and similar non-modular filesystems do not need a rcu_barrier
> > in deactivate_locked_super.  Being non-modular there is no danger
> > of the rcu callback running after the module is unloaded.
> 
> There's more than just a module unload there, though - actual freeing
> struct super_block also happens past that rcu_barrier()...

Is there anything in there for which synchronous operation is required?
If not, one approach would be to drop the rcu_barrier() calls to a
workqueue or something similar.

							Thanx, Paul