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From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH] vfs: dont chain pipe/anon/socket on superblock s_inodes
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Date: Tue, 26 Jul 2011 07:49:06 -0400
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Cc: Christoph Hellwig <hch@infradead.org>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Al Viro <viro@ZenIV.linux.org.uk>,
	David Miller <davem@davemloft.net>,
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	Anton Blanchard <anton@samba.org>, npiggin@kernel.dk,
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To: Eric Dumazet <eric.dumazet@gmail.com>
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On Tue, Jul 26, 2011 at 12:43:33PM +0200, Eric Dumazet wrote:
> BTW, we have one atomic op that could be avoided in new_inode()
> 
> spin_lock(&inode->i_lock);
> inode->i_state = 0;
> spin_unlock(&inode->i_lock);
> 
> can probably be changed to something less expensive...
> 
> inode->i_state = 0;
> smp_wmb();
> 
> Not clear if we really need a memory barrier either....

I think we already had this in some of the earlier vfs/inode scale
series, but it got lost when Al asked to just put the fundamental
changes in.

For plain new_inode() the barrier shouldn't be needed as we take
the sb list lock just a little later.  I'm not sure about your new
variant, so I'll rather lave that to you.

There's a few other things missing from earlier iterations, most notable
the non-atomic i_count, and the bucket locks for the inode hash, if
you're eager enough to look into that area.