linux-kernel - Re: [uml-devel] [PATCH 2/2] UML

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Date:	Wed, 20 Jun 2007 16:06:58 +0200
From:	Blaisorblade <blaisorblade@...oo.it>
To:	user-mode-linux-devel@...ts.sourceforge.net
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jeff Dike <jdike@...toit.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [uml-devel] [PATCH 2/2] UML - Add stack usage monitoring

On martedì 19 giugno 2007, Andrew Morton wrote:
> On Tue, 19 Jun 2007 15:50:03 -0400
>
> Jeff Dike <jdike@...toit.com> wrote:
> > On Tue, Jun 19, 2007 at 11:54:22AM -0700, Andrew Morton wrote:
> > > On Tue, 19 Jun 2007 14:42:45 -0400
> > >
> > > Jeff Dike <jdike@...toit.com> wrote:
> > > > Add a machanism to see how much of a kernel stack is used.  This
> > > > allocates zeroed stacks and sees where the lowest non-zero byte is on
> > > > process exit.  It keeps track of the lowest value and logs values as
> > > > they get lower.
> > >
> > > remind us again why the generic code is unsuitable?
> >
> > It does something different - it will tell you the greatest stack
> > usage of any currently running process.  What I want to be able to do
> > is run a workload and come back a few days later and see how close
> > anything came to running out of stack.
>
> <looks>
>
> wth?  I'm _sure_ we used to have code in there which would, within
> do_exit(), work out the maximum amount of kernel stack which a task had
> used and if that was max-since-boot, drop a printk.
>
> Maybe I dreamed it, but I don't think so.
>
> I wonder where it went?

Oh, it's exactly what CONFIG_DEBUG_STACK_USAGE does for i386... (not sure if 
you were still wondering...).

> Oh well.  Your new code should really be generic, utilising the
> stack-page-zeroing which CONFIG_DEBUG_STACK_USAGE enables.  There's nothing
> UML-specific about it.

> low_water_lock and lowest_to_date should be static to check_stack_usage(),
> btw..

-- 
Inform me of my mistakes, so I can add them to my list!
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade
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