linux-kernel - Re: [patch 00/41] cpu alloc / cpu ops v3: Optimize per cpu access

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Date:	Thu, 29 May 2008 23:37:58 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Lameter <clameter@....com>
Cc:	Eric Dumazet <dada1@...mosbay.com>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org, David Miller <davem@...emloft.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Mike Travis <travis@....com>
Subject: Re: [patch 00/41] cpu alloc / cpu ops v3: Optimize per cpu access

On Thu, 29 May 2008 23:22:31 -0700 (PDT) Christoph Lameter <clameter@....com> wrote:

> On Thu, 29 May 2008, Andrew Morton wrote:
> 
> > ext3 maintains three percpu_counters per mount.  Each percpu_counter
> > does one percpu_alloc.  People can mount an arbitrary number of ext3
> > filesystems!
> 
> But its 4 bytes per alloc right?

It could be 4000.  The present alloc_percpu() would support that.

And struct nfs_iostats is 264 bytes and nfs does an alloc_percpu() of
one of those per server and mounting thousands of servers per client
is, I believe, a real-world operation.

Plus for the entyenth time: saying that this code will probably work
acceptably for most people in 2.6.26 is not sufficient!
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