linux-kernel - Re: [PATCH 15/18] fs: introduce a per-cpu last

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Message-ID: <20101008095824.GB19804@ZenIV.linux.org.uk>
Date:	Fri, 8 Oct 2010 10:58:24 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Dave Chinner <david@...morbit.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 15/18] fs: introduce a per-cpu last_ino allocator

On Fri, Oct 08, 2010 at 10:22:34AM +0200, Andi Kleen wrote:
> Dave Chinner <david@...morbit.com> writes:
> 
> > From: Eric Dumazet <eric.dumazet@...il.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.
> 
> But looks reasonable, although it would be better to simply fix 
> sockets/pipes/etc. to not allocate an inode numbers.

Can be done if you bother to add ->getattr() for those, but you'll need
to do some kind of lazy allocation of inumbers for those; fstat() _will_
want st_ino.
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