On Tue, 30 Jun 2009, David Rientjes wrote:
> I don't see how that's different from enabling debugging on all caches
> like CONFIG_SLAB_DEBUG_ON currently does and then warning at the time of
> slab allocation failure that it may be the result of the debugging
> metadata so the user can subsequently prevent it. In other words, if we
> use MAX_DEBUG_SIZE as Pekka originally implemented as
> (3 * sizeof(void *) + 2 * sizeof(struct track)), do this:
I like it.
> diff --git a/mm/slub.c b/mm/slub.c
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -142,6 +142,11 @@
> SLAB_POISON | SLAB_STORE_USER)
>
> /*
> + * The maximum amount of metadata added to a slab when debugging is enabled.
> + */
> +#define MAX_DEBUG_SIZE (3 * sizeof(void *) + 2 * sizeof(struct track))
> +
> +/*
> * Set of flags that will prevent slab merging
> */
> #define SLUB_NEVER_MERGE (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \
> @@ -1561,6 +1566,21 @@ slab_out_of_memory(struct kmem_cache *s, gfp_t gfpflags, int nid)
> "default order: %d, min order: %d\n", s->name, s->objsize,
> s->size, oo_order(s->oo), oo_order(s->min));
>
> + if (s->flags & (SLAB_POISON | SLAB_RED_ZONE | SLAB_STORE_USER)) {
> + int min_order;
> +
> + /*
> + * Debugging is enabled, which may increase oo_order(s->min), so
> + * warn the user that allocation failures may be avoided if
> + * debugging is enabled for this cache.
> + */
> + min_order = get_order(s->size - MAX_DEBUG_SIZE);
> + if (min_order < oo_order(s->min))
> + printk(KERN_WARNING " %s debugging increased min order "
> + "from %d to %d, use slab_debug=-,%s to disable.",
> + s->name, min_order, oo_order(s->min), s->name);
It may be easier to check the order of the initial size vs. the order of
the size with all metadata
if (get_order(s->size) > get_order(s->objsize)
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