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 <vba...@suse.cz>
---
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
