linux-kernel - Re: [RFC/PATCH 6/8]: CGroup Files: Remove cpuset_common_file

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Date:	Tue, 13 May 2008 14:27:24 -0700
From:	"Paul Menage" <menage@...gle.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	pj@....com, xemul@...nvz.org, balbir@...ibm.com, serue@...ibm.com,
	linux-kernel@...r.kernel.org, containers@...ts.linux-foundation.org
Subject: Re: [RFC/PATCH 6/8]: CGroup Files: Remove cpuset_common_file_write()

On Tue, May 13, 2008 at 1:11 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Mon, 12 May 2008 23:37:13 -0700
>  menage@...gle.com wrote:
>
>  > @@ -1412,14 +1355,18 @@ static struct cftype files[] = {
>  >       {
>  >               .name = "cpus",
>  >               .read = cpuset_common_file_read,
>  > -             .write = cpuset_common_file_write,
>  > +             .write_string = update_cpumask,
>  > +             .max_write_len = (100U + 6 * NR_CPUS),
>
>  hm, magic handwavy surely-enough-for-anyone constants.

This is just a movement of the check previously in cpuset_common_file_write():

	/* Crude upper limit on largest legitimate cpulist user might write. */
	if (nbytes > 100U + 6 * max(NR_CPUS, MAX_NUMNODES))
		return -E2BIG;

I'll add more comments. But I think it's a reasonable limit - assuming
that you wastefully enumerate each cpu individually, separated by
commas, 6 * NR_CPUS is enough for 100K CPUs.

Paul
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