Re: [PATCH] slub: reduce total stack usage of slab_err & object_err

Richard Kennedy
2008-09-30T16:21:18Z

On Tue, 2008-09-30 at 10:38 -0500, Christoph Lameter wrote:
> Richard Kennedy wrote:
> > reduce the total stack usage of slab_err & object_err.
> >
> > Introduce a new function to display a simple slab bug message, and call
> > this when vprintk is not needed.
>
> You could simply get rid of the 100 byte buffer by using vprintk? Same method
> could be used elsewhere in the kernel and does not require additional
> functions. Compiles, untestted.
>
>
>
>
> Subject: Slub reduce slab_bug stack usage by using vprintk
>
> Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
>
> Index: linux-2.6/mm/slub.c
> ===================================================================
> --- linux-2.6.orig/mm/slub.c 2008-09-30 10:34:40.000000000 -0500
> +++ linux-2.6/mm/slub.c 2008-09-30 10:36:10.000000000 -0500
> @@ -422,15 +422,14 @@
> static void slab_bug(struct kmem_cache *s, char *fmt, ...)
> {
> va_list args;
> - char buf[100];
>
> va_start(args, fmt);
> - vsnprintf(buf, sizeof(buf), fmt, args);
> - va_end(args);
> printk(KERN_ERR "========================================"
> "=====================================\n");
> - printk(KERN_ERR "BUG %s: %s\n", s->name, buf);
> - printk(KERN_ERR "----------------------------------------"
> + printk(KERN_ERR "BUG %s: ", s->name);
> + vprintk(fmt, args);
> + va_end(args);
> + printk(KERN_ERR "\n----------------------------------------"
> "-------------------------------------\n\n");
> }
>
Yes, using vprintk is better but you still have this path :
( with your patch applied)

object_err -> slab_bug(208) -> printk(216)
instead of
object_err -> slab_bug_message(8) -> printk(216)

unfortunately the overhead for having var_args is pretty big, at least
on x86_64. I haven't measured it on 32 bit yet.

Richard