linux-kernel - Re: [PATCH] vfs: Speed up deactivate

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Message-ID: <20120507235647.GH21152@linux.vnet.ibm.com>
Date:	Mon, 7 May 2012 16:56:47 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Louis Rilling <louis.rilling@...labs.com>,
	Mike Galbraith <efault@....de>,
	Christoph Hellwig <hch@...radead.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] vfs: Speed up deactivate_super for non-modular
 filesystems

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

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