linux-kernel - Re: [PATCH] vfs: dont chain pipe/anon/socket on superblock s

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Message-ID: <20110726114906.GA19975@infradead.org>
Date:	Tue, 26 Jul 2011 07:49:06 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	David Miller <davem@...emloft.net>,
	Andi Kleen <andi@...stfloor.org>,
	Matthew Wilcox <matthew@....cx>,
	Anton Blanchard <anton@...ba.org>, npiggin@...nel.dk,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] vfs: dont chain pipe/anon/socket on superblock s_inodes
 list

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.

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