netdev - Re: [PATCH] NET : convert ip_rt_acct to per

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Message-Id: <20071116103546.8320d985.dada1@cosmosbay.com>
Date:	Fri, 16 Nov 2007 10:35:46 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] NET : convert ip_rt_acct to per_cpu variables

On Fri, 16 Nov 2007 01:12:43 -0800 (PST)
David Miller <davem@...emloft.net> wrote:

> From: Eric Dumazet <dada1@...mosbay.com>
> Date: Fri, 16 Nov 2007 09:59:03 +0100
> 
> > [PATCH] NET : NET_CLS_ROUTE : convert ip_rt_acct to per_cpu variables
> > 
> > ip_rt_acct needs 4096 bytes per cpu to perform some accounting.
> > It is actually allocated as a single huge array [4096*NR_CPUS]
> > (rounded up to a power of two)
> > 
> > Converting it to a per cpu variable is wanted to :
> >  - Save space on machines were num_possible_cpus() < NR_CPUS
> >  - Better NUMA placement (each cpu gets memory on its node)
> > 
> > Signed-off-by: Eric Dumazet <dada1@...mosbay.com>
> 
> This is better in one sense but worse in another.
> 
> At least the previous code dynamically allocated the thing,
> now at least one copy is taking up core kernel text image
> space.

Oh I see, you think that adding 4096 null bytes to the static percpu area might be a problem.

> 
> I think it's an alloc_percpu() candidate, what do you think?
> 

Yes absolutely, I will submit a new version.

Thank you

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