linux-kernel - Re: [PATCH 07/17] fs: icache atomic inodes

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Date:	Sat, 16 Oct 2010 18:56:41 +1100
From:	Nick Piggin <npiggin@...nel.dk>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Dave Chinner <david@...morbit.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/17] fs: icache atomic inodes_stat

On Wed, Sep 29, 2010 at 09:52:53PM -0700, Andrew Morton wrote:
> On Wed, 29 Sep 2010 22:18:39 +1000 Dave Chinner <david@...morbit.com> wrote:
> > From: Nick Piggin <npiggin@...e.de>
> > 
> > The inode use statistics are currently protected by the inode_lock.
> > Before we can remove the inode_lock, we need to protect these
> > counters against races. Do this by converting them to atomic
> > counters so they ar enot dependent on any lock at all.
> 
> typo

It's Dave, I swear :)


> > +struct inodes_stat_t {
> > +	atomic_t nr_inodes;
> > +	atomic_t nr_unused;
> > +	int dummy[5];		/* padding for sysctl ABI compatibility */
> > +};
> 
> OK, that's a hack.  The first two "ints" are copied out to userspace. 
> This change assumes that sizeof(atomic_t)=4 and that an atomic_t has
> the same layout, alignment and padding as an int.
> 
> Probably that's true in current kernels and with current architectures
> but it's a hack and it's presumptive.
> 
> It shouldn't be snuck into the tree unchangelogged and uncommented.
> 
> (time passes)
> 
> OK, I see that all of this gets reverted later on.  Please update the
> changelog so the next reviewer doesn't get fooled.

Yeah it is. I might end up folding the per-cpu stuff back over it
and avoid the issue completely. Otherwise I'll add a comment.

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