linux-kernel - Re: Nick's vfs-scalability patches ported to 2.6.33-rt

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Date:	Wed, 03 Mar 2010 15:31:30 -0800
From:	john stultz <johnstul@...ibm.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	lkml <linux-kernel@...r.kernel.org>,
	Clark Williams <williams@...hat.com>,
	John Kacur <jkacur@...hat.com>
Subject: Re: Nick's vfs-scalability patches ported to 2.6.33-rt

On Fri, 2010-02-26 at 17:01 +1100, Nick Piggin wrote:
> On Thu, Feb 25, 2010 at 09:53:28PM -0800, john stultz wrote:
> > Hey Thomas, Nick,
> > 	I just wanted to let you know I've just finished forward porting Nick's
> > patches to 2.6.33-rc8-rt2.  Luckily my forward port of Nick's patches to
> > 2.6.33 applies on top of the -rt tree without any collisions, and I've
> > added a handful of maybe sketchy fixups to get it working with -rt.
> > 
> > You can find the patchset here:
> > http://sr71.net/~jstultz/dbench-scalability/patches/2.6.33-rc8-rt2/vfs-scale.33-rt.tar.bz2
> > 
> > Here's a chart showing how much these patches help dbench numbers on
> > ramfs:
> > http://sr71.net/~jstultz/dbench-scalability/graphs/2.6.33/ramfs-dbench.png
> > 
> > I've not done any serious stress testing with the patchset yet, but
> > wanted to post it for your review.
> > 
> > Nick: I'd appreciate any feedback as to if any of my forward porting has
> > gone awry. I'm still very green with respect to the vfs, so I don't
> > doubt there are some issues hiding here.
> 
> BTW there are a few issues Al pointed out. We have to synchronize RCU
> after unregistering a filesystem so d_ops/i_ops doesn't go away, and
> mntput can sleep so we can't do it under RCU read lock.

Does the following address this issue properly?

Signed-off-by: John Stultz <johnstul@...ibm.com>

diff --git a/fs/filesystems.c b/fs/filesystems.c
index a24c58e..3448e7c 100644
--- a/fs/filesystems.c
+++ b/fs/filesystems.c
@@ -110,6 +110,7 @@ int unregister_filesystem(struct file_system_type * fs)
 			*tmp = fs->next;
 			fs->next = NULL;
 			write_unlock(&file_systems_lock);
+			synchronize_rcu();
 			return 0;
 		}
 		tmp = &(*tmp)->next;


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