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From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 15/18] fs: introduce a per-cpu last_ino allocator
Date: Fri, 8 Oct 2010 04:44:41 -0400
Message-ID: <20101008084441.GA17366@infradead.org>
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Cc: Dave Chinner <david@fromorbit.com>, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org
To: Andi Kleen <andi@firstfloor.org>
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On Fri, Oct 08, 2010 at 10:22:34AM +0200, Andi Kleen wrote:
> Dave Chinner <david@fromorbit.com> writes:
> 
> > From: Eric Dumazet <eric.dumazet@gmail.com>
> >
> > new_inode() dirties a contended cache line to get increasing
> > inode numbers. This limits performance on workloads that cause
> > significant parallel inode allocation.
> >
> > Solve this problem by using a per_cpu variable fed by the shared
> > last_ino in batches of 1024 allocations.  This reduces contention on
> > the shared last_ino, and give same spreading ino numbers than before
> > (i.e. same wraparound after 2^32 allocations).
> 
> This doesn't help for Unix disk file systems, so not fully sure why you
> need it for XFS.

Currently i_ino is assigned for every inode allocated using new_inode.
It's pretty stupid as most callers simply don't need it.  But Dave
didn't want to make this series even more complicated than nessecary
and leave sorting this out for later.