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> > --- > 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 Yet another potential future user of DEFINE_STATIC_KEY_MAYBE()[1], once I get it landed. :) Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> [1] https://lore.kernel.org/lkml/20200324203231.64324-2-keescook@xxxxxxxxxxxx/ -- Kees Cook
