linux-kernel - Re: [PATCH 2/2] UML - Add stack usage monitoring

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Message-Id: <20070619131441.01b5ae4b.akpm@linux-foundation.org>
Date:	Tue, 19 Jun 2007 13:14:41 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jeff Dike <jdike@...toit.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	uml-devel <user-mode-linux-devel@...ts.sourceforge.net>
Subject: Re: [PATCH 2/2] UML - Add stack usage monitoring

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 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..

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