linux-kernel - Re: thread stacks and strict vm overcommit accounting

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Message-Id: <20070315153613.3d2eaf10.akpm@linux-foundation.org>
Date:	Thu, 15 Mar 2007 15:36:13 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Hugh Dickins <hugh@...itas.com>, Dan Aloni <da-x@...atomic.org>,
	linux-kernel@...r.kernel.org
Subject: Re: thread stacks and strict vm overcommit accounting

On Thu, 15 Mar 2007 23:33:43 +0000
Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> > Stack RSS should certainly be included in Committed_AS,
> > but RLIMIT_STACK merely limits how big the stack vma may grow to:
> > at any moment the stack vma is probably very much smaller,
> > and only its current size is accounted in Committed_AS.
> 
> With a typical size as a fuzz factor preaccounted in later kernels.

Where's that done?

> > > > Is this the intended behaviour?
> > > 
> > > That sounds like a bug to me.
> > 
> > I'm suspecting it's an oddity rather than a bug.
> 
> It is intended behaviour.

Each instance of

main()
{
	sleep(100);
}

appears to increase Committed_AS by around 200kb.  But we've committed to
providing it with 8MB for stack.

How come this is correct?

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