linux-kernel - Re: [RFC] Reorganizing structs to save space

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Date:	Tue, 3 Apr 2007 16:30:29 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] Reorganizing structs to save space

On Tue, Apr 03, 2007 at 09:28:48AM -0300, Arnaldo Carvalho de Melo wrote:
> module                     16960 16848 112

That's huge.

> 	struct module_ref          ref[255];             /*   480 16320 */

Huh. That's this:

struct module_ref
{
        local_t count;
} ____cacheline_aligned;

This is horrible. Surely there's some way to do better than a
cacheline per module per possible CPU. We should only need 4 bytes per
module per online CPU.

And really, about the only case where we actually care about cacheline
bouncing here at all is on modules that do this per-packet. Just about
everyone else can get by with 4 bytes per module total.

-- 
Mathematics is the supreme nostalgia of our time.
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