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

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Message-ID: <20100422170801.GZ5677@sgi.com>
Date:	Thu, 22 Apr 2010 12:08:02 -0500
From:	Robin Holt <holt@....com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	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>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Robin Holt <holt@....com>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Patch 1/1] init: Provide a kernel start parameter to increase
 pid_max v2

> 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.

Robin
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