On Wed, Jun 10, 2020 at 06:31:32PM +0200, Vlastimil Babka wrote:
> One advantage of CONFIG_SLUB_DEBUG is that a generic distro kernel can be built
> with the option enabled, but it's inactive until simply enabled on boot,
> without rebuilding the kernel. With a static key, we can further eliminate the
> overhead of checking whether a cache has a particular debug flag enabled if we
> know that there are no such caches (slub_debug was not enabled during boot). We
> use the same mechanism also for e.g. page_owner, debug_pagealloc or kmemcg
> functionality.
>
> This patch introduces the static key and makes the general check for per-cache
> debug flags kmem_cache_debug() use it. This benefits several call sites,
> including (slow path but still rather frequent) __slab_free(). The next patches
> will add more uses.
>
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: Roman Gushchin <guro@xxxxxx>
Thanks!
> ---
> mm/slub.c | 16 +++++++++++++---
> 1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 8dd2925448ae..24d3e5f832aa 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -114,13 +114,21 @@
> * the fast path and disables lockless freelists.
> */
>
> +#ifdef CONFIG_SLUB_DEBUG
> +#ifdef CONFIG_SLUB_DEBUG_ON
> +DEFINE_STATIC_KEY_TRUE(slub_debug_enabled);
> +#else
> +DEFINE_STATIC_KEY_FALSE(slub_debug_enabled);
> +#endif
> +#endif
> +
> static inline int kmem_cache_debug(struct kmem_cache *s)
> {
> #ifdef CONFIG_SLUB_DEBUG
> - return unlikely(s->flags & SLAB_DEBUG_FLAGS);
> -#else
> - return 0;
> + if (static_branch_unlikely(&slub_debug_enabled))
> + return s->flags & SLAB_DEBUG_FLAGS;
> #endif
> + return 0;
> }
>
> void *fixup_red_left(struct kmem_cache *s, void *p)
> @@ -1389,6 +1397,8 @@ static int __init setup_slub_debug(char *str)
> slub_debug_string = saved_str;
> }
> out:
> + if (slub_debug != 0 || slub_debug_string)
> + static_branch_enable(&slub_debug_enabled);
> if ((static_branch_unlikely(&init_on_alloc) ||
> static_branch_unlikely(&init_on_free)) &&
> (slub_debug & SLAB_POISON))
> --
> 2.26.2
>
