linux-kernel - Re: [PATCH v2 1/2] slub: Enable backtrace for create/delete points.

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Message-ID: <alpine.DEB.2.00.1107010905350.2458@router.home>
Date:	Fri, 1 Jul 2011 09:08:26 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Ben Greear <greearb@...delatech.com>
cc:	penberg@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] slub: Enable backtrace for create/delete
 points.

On Tue, 28 Jun 2011, greearb@...delatech.com wrote:

> diff --git a/mm/slub.c b/mm/slub.c
> index 35f351f..3477ce5 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -191,8 +191,12 @@ static LIST_HEAD(slab_caches);
>  /*
>   * Tracking user of a slab.
>   */
> +#define TRACK_ADDRS_COUNT 16
>  struct track {
> -	unsigned long addr;	/* Called from address */
> +	unsigned long caddr;

Keep the name the same since its role does not change. That makes the
patch touch less code.

> +#ifdef CONFIG_STACKTRACE
> +	unsigned long addrs[TRACK_ADDRS_COUNT];	/* Called from address */
> +#endif
>  	int cpu;		/* Was running on cpu */
>  	int pid;		/* Pid context */
>  	unsigned long when;	/* When did the operation occur */
> @@ -420,7 +424,25 @@ static void set_track(struct kmem_cache *s, void *object,
>  	struct track *p = get_track(s, object, alloc);
>
>  	if (addr) {
> -		p->addr = addr;
> +#ifdef CONFIG_STACKTRACE
> +		struct stack_trace trace;
> +		int i;
> +
> +		trace.nr_entries = 0;
> +		trace.max_entries = TRACK_ADDRS_COUNT;
> +		trace.entries = p->addrs;
> +		trace.skip = 3;
> +		save_stack_trace(&trace);
> +
> +		/* See rant in lockdep.c */
> +		if (trace.nr_entries != 0 &&
> +		    trace.entries[trace.nr_entries - 1] == ULONG_MAX)
> +			trace.nr_entries--;
> +
> +		for (i = trace.nr_entries; i < TRACK_ADDRS_COUNT; i++)
> +			p->addrs[i] = 0;
> +#endif

Hmmm... Is this really working on all architectures? I remember from years
past that we had issues with adding the same functionality to slab.

Otherwise the patch is quite straightforward (and it will be much cleaner
if you do not change the name of "addr").

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