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

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Message-Id: <20070619125707.84cf73fd.randy.dunlap@oracle.com>
Date:	Tue, 19 Jun 2007 12:57:07 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Jeff Dike <jdike@...toit.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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 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.
> 
> Signed-off-by: Jeff Dike <jdike@...ux.intel.com>
> --
>  arch/um/Kconfig.debug        |    9 +++++++++
>  arch/um/defconfig            |    1 +
>  arch/um/kernel/process.c     |   29 +++++++++++++++++++++++++++++
>  include/asm-um/thread_info.h |   16 ++++++++++++++++
>  4 files changed, 55 insertions(+)
> 
> Index: linux-2.6.21-mm/arch/um/Kconfig.debug
> ===================================================================
> --- linux-2.6.21-mm.orig/arch/um/Kconfig.debug	2007-06-19 14:06:36.000000000 -0400
> +++ linux-2.6.21-mm/arch/um/Kconfig.debug	2007-06-19 14:06:44.000000000 -0400
> @@ -47,4 +47,13 @@ config GCOV
>          If you're involved in UML kernel development and want to use gcov,
>          say Y.  If you're unsure, say N.
>  
> +config DEBUG_STACK_USAGE
> +	bool "Stack utilization instrumentation"
> +	default N
> +	help
> +	Track the maximum kernel stack usage - this will look at each
> +	kernel stack at process exit and log it if it's the deepest
> +	stack seen so far.

Kconfig help text is indented 2 more spaces (by convention or
CodingStyle).

> +
> +	This option will slow down process creation and destruction somewhat.
>  endmenu
> Index: linux-2.6.21-mm/arch/um/kernel/process.c
> ===================================================================
> --- linux-2.6.21-mm.orig/arch/um/kernel/process.c	2007-06-19 14:06:36.000000000 -0400
> +++ linux-2.6.21-mm/arch/um/kernel/process.c	2007-06-19 15:48:20.000000000 -0400
> @@ -411,3 +411,32 @@ unsigned long arch_align_stack(unsigned 
>  	return sp & ~0xf;
>  }
>  #endif
> +
> +#ifdef CONFIG_DEBUG_STACK_USAGE
> +
> +static DEFINE_SPINLOCK(low_water_lock);
> +static int lowest_to_date = THREAD_SIZE;
> +
> +void check_stack_usage(struct thread_info *s)
> +{
> +	unsigned int *stack, *p, *end;
> +	int left;
> +
> +	stack = (unsigned int *) (s + 1);
> +	end = (unsigned int *) ((unsigned long) s + THREAD_SIZE);
> +	for (p = stack; p < end; p++) {
> +		if(*p != 0)

		if (*p != NULL)
or
		if (*p)

> +			break;
> +	}
> +
> +	left = (p - stack) * sizeof(*p);
> +
> +	spin_lock(&low_water_lock);
> +	if (left < lowest_to_date) {
> +		printk("Greatest stack depth - %d bytes left\n", left);

Does UML need/use KERN_* facility levels in printk() calls?

> +		lowest_to_date = left;
> +	}
> +	spin_unlock(&low_water_lock);
> +}
> +
> +#endif

---
~Randy
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