linux-kernel - Re: [MM] Make mm counters per cpu instead of atomic

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Message-Id: <20091106084238.cbecd8ef.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 6 Nov 2009 08:42:38 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	"hugh.dickins@...cali.co.uk" <hugh.dickins@...cali.co.uk>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, Tejun Heo <tj@...nel.org>
Subject: Re: [MM] Make mm counters per cpu instead of atomic

On Thu, 5 Nov 2009 10:10:56 -0500 (EST)
Christoph Lameter <cl@...ux-foundation.org> wrote:

> On Thu, 5 Nov 2009, KAMEZAWA Hiroyuki wrote:
> 
> > Hmm, I don't fully understand _new_ percpu but...
> > In logical (even if not realistic), x86-32 supports up to 512 ? cpus in Kconfig.
> > BIGSMP.
> 
> x86-32 only supports 32 processors. Plus per cpu areas are only allocated
> for the possible processors.
> 
My number is just from Kconfig.

> > Then, if 65536 process runs, this consumes
> >
> > 65536(nr_proc) * 8 (size) * 512(cpus) = 256MBytes.
> 
> With 32 possible cpus this results in 16m of per cpu space use.
> 
If swap_usage is added, 24m, 25% of vmalloc area.
(But, yes, returning -ENOMEM to fork() is ok to me, 65536 proc are extreme.)

Thanks,
-Kame

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