linux-kernel - Re: [Patch 1/1] init: Provide a kernel start parameter to increase pid

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Message-Id: <20100422133505.6e7a24ad.akpm@linux-foundation.org>
Date:	Thu, 22 Apr 2010 13:35:05 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Robin Holt <holt@....com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, Greg KH <gregkh@...e.de>,
	Rik van Riel <riel@...hat.com>,
	John Stoffel <john@...ffel.org>, Hedi Berriche <hedi@....com>,
	Mike Travis <travis@....com>, Ingo Molnar <mingo@...e.hu>,
	Jack Steiner <steiner@....com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Patch 1/1] init: Provide a kernel start parameter to increase
 pid_max v2

On Thu, 22 Apr 2010 12:08:02 -0500
Robin Holt <holt@....com> wrote:

> > Which I'm not entirely sure makes the case for the kernel parameter much 
> > stronger, though. I wonder if it's not more appropriate to just have a 
> > total hack saying
> > 
> > 	if (max_pids < N * max_cpus) {
> > 		printk("We have %d CPUs, increasing max_pids to %d\n");
> > 		max_pids = N*max_cpus;
> > 	}
> > 
> > where "N" is just some random fudge-factor. It's reasonable to expect a 
> > certain minimum number of processes per CPU, after all.
> 
> How about:
> 
> 	pid_max_min = max(pid_max_min, 19 * num_possible_cpus());
> 	pid_max_baseline = 2048 * num_possible_cpus();
> 
> 	if (pid_max < pid_max_baseline) {
> 		printk("We have %d CPUs, increasing pid_max to %d\n"...
> 		pid_max = pid_max_baseline;
> 	}
> 
> 
> This would scale pid_max_min by a sane amount, leave the default value
> of pid_max_min and pid_max untouched below 16 cpus and then scale both
> up linearly beyond that.

Something like that would work.  We shouild ensure that pid_max cannot
end up being less than the current PID_MAX_DEFAULT.

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