linux-kernel - Re: [PATCH 15/17] fs: inode per-cpu last

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Date:	Wed, 6 Oct 2010 17:29:21 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	dada1@...mosbay.com, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 15/17] fs: inode per-cpu last_ino allocator

On Wed, Sep 29, 2010 at 10:07:59PM -0400, Christoph Hellwig wrote:
> On Wed, Sep 29, 2010 at 10:18:47PM +1000, Dave Chinner wrote:
> > From: Eric Dumazet <dada1@...mosbay.com>
> > 
> > last_ino was converted to an atomic variable to allow the inode_lock
> > to go away. However, contended atomics do not scale on large
> > machines, and new_inode() triggers excessive contention in such
> > situations.
> 
> And the good thing is most users of new_inode couldn't care less about
> the fake i_ino assigned because they have a real inode number.  So
> the first step is to move the i_ino assignment into a separate helper
> and only use it in those filesystems that need it.  Second step is
> to figure out why some filesystems need iunique() and some are fine
> with the incrementing counter and then we should find a scalable way
> to generate an inode number - preferably just one and not to, but if
> that's not possible we need some documentation on why which one is
> needed.

Sounds like a good plan, but I don't really have time right now to
understand the iget routines of every single filesystem to determine
which rely on the current new_inode() allocated inode number. I
think that is best left for a later cleanup, seeing as the
last_ino scalability problem is easily addressed....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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