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

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Message-ID: <20101008100944.GE13352@basil.fritz.box>
Date:	Fri, 8 Oct 2010 12:09:44 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Andi Kleen <andi@...stfloor.org>,
	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 10:58:24AM +0100, Al Viro wrote:
> 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.

Why not just put 0 in st_ino for sockets/pipes/etc. ? 

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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