linux-kernel - Re: [patch 04/33] fs: brlock vfsmount

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Date:	Sun, 27 Sep 2009 21:56:19 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 04/33] fs: brlock vfsmount_lock

On Tue, Sep 22, 2009 at 04:17:51PM +0100, Al Viro wrote:
> On Fri, Sep 04, 2009 at 04:51:45PM +1000, npiggin@...e.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.

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