linux-kernel - Re: [patch 02/28] pm_qos: clean up racy global "name" variable

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Date:	Sat, 10 Oct 2009 22:09:22 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jonathan Corbet <corbet@....net>
Cc:	John Kacur <jkacur@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Vincent Sanders <vince@...tec.co.uk>,
	Christoph Hellwig <hch@...radead.org>,
	Mark Gross <mgross@...ux.intel.com>
Subject: Re: [patch 02/28] pm_qos: clean up racy global "name" variable

On Sat, 2009-10-10 at 14:03 -0600, Jonathan Corbet wrote:
> On Sat, 10 Oct 2009 21:54:22 +0200 (CEST)
> John Kacur <jkacur@...hat.com> wrote:
> 
> > Hmnn, why 32? Seems arbitrary. At least you see with "process_1234567890" 
> > which is 19, an attempt to show what the maximum string size would be. If 
> > a system were configured to enlarge the maximum PID from 32767 to 4194303 
> > that would still only be 7 digits, so "process_1234567" - which is 16 
> > digits with the newline would enough.
> > 
> > So, I suggest you change that to
> > #define PID_NAME_LEN sizeof("process_1234567")
> 
> ....which works great until somebody enables 64-bit process IDs...:)

PID/TIDs are limited to 2^29, raising it above that will break things
like futexes. Raising it above 2^32 will break heaps of userspace.

That said, 512M tasks still seems like a lot, but if history is
something to go by we'll eventually run out...

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