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

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Date:	Thu, 29 May 2008 23:22:31 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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, 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?

> Another: there are two percpu_counters (and hence two percpu_alloc()s)
> per backing_dev_info.  One backing_dev_info per disk and people have
> been known to have thousands (iirc ~10,000) disks online.

8 bytes per backing device. 80000 bytes for 10000 disks.

> And those examples were plucked only from today's kernel.  Who knows
> what other problems will be in 2.6.45?

We can always increase the sizes.
 
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