linux-kernel - Re: [uml-devel] [PATCH 4/5] UML - Simplify helper stack handling

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Message-Id: <20070703085830.9b0520a1.akpm@linux-foundation.org>
Date:	Tue, 3 Jul 2007 08:58:30 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Blaisorblade <blaisorblade@...oo.it>
Cc:	user-mode-linux-devel@...ts.sourceforge.net,
	Jeff Dike <jdike@...toit.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [uml-devel] [PATCH 4/5] UML - Simplify helper stack handling

On Tue, 3 Jul 2007 17:28:30 +0200 Blaisorblade <blaisorblade@...oo.it> wrote:

> On giovedì 28 giugno 2007, Andrew Morton wrote:
> > So I'm running the generic version of this on i386 with 8k stacks (below),
> > with a quick LTP run.
> >
> > Holy cow, either we use a _lot_ of stack or these numbers are off:
> >
> > vmm:/home/akpm> dmesg -s 1000000|grep 'bytes left'
> > khelper used greatest stack depth: 7176 bytes left
> > khelper used greatest stack depth: 7064 bytes left
> > khelper used greatest stack depth: 6840 bytes left
> > khelper used greatest stack depth: 6812 bytes left
> > hostname used greatest stack depth: 6636 bytes left
> > uname used greatest stack depth: 6592 bytes left
> > uname used greatest stack depth: 6284 bytes left
> > hotplug used greatest stack depth: 5568 bytes left
> > rpc.nfsd used greatest stack depth: 5136 bytes left
> > chown02 used greatest stack depth: 4956 bytes left
> > fchown01 used greatest stack depth: 4892 bytes left
> 
> > That's the sum of process stack and interrupt stack, but I doubt if this
> > little box is using much interrupt stack space.
> >
> > No wonder people are still getting stack overflows with 4k stacks...
> 
> First, those numbers pretend to be _unused_ stack space.

Yep.  So fchown01 used ~3200 bytes of stack.  Problem.

> Well, UML tends to use more stack space than the rest of kernel.

That was a plain old i386 kernel.

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