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

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Message-ID: <20070316144342.GF355@devserv.devel.redhat.com>
Date:	Fri, 16 Mar 2007 09:43:42 -0500
From:	Jakub Jelinek <jakub@...hat.com>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Dan Aloni <da-x@...atomic.org>, linux-kernel@...r.kernel.org
Subject: Re: thread stacks and strict vm overcommit accounting

On Thu, Mar 15, 2007 at 11:08:40PM +0000, Hugh Dickins wrote:
> > appears to increase Committed_AS by around 200kb.  But we've committed to
> > providing it with 8MB for stack.
> > 
> > How come this is correct?
> 
> We've no more committed to providing each instance with 8MB of stack,
> than we've committed to providing each instance with RLIMIT_AS of
> address space.  The rlimits are limits, not commitments, surely?

RLIMIT_STACK only applies to the initial thread, POSIX threads have just
stack size attribute, not maximum thread stack size attribute.
If you set it explicitly with pthread_attr_setstacksize, then libpthread
will honor whatever thread stack size you want, otherwise it just uses
some default thread stack size.  This happens to be in NPTL derived
from RLIMIT_STACK value, but very well could be something else.

	Jakub
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