Commit ca0cab65 authored Aug 06, 2020 by Vlastimil Babka Committed by Linus Torvalds Aug 07, 2020

mm, slub: introduce static key for slub_debug()



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@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Jann Horn <jannh@google.com>
Cc: Vijayanand Jitta <vjitta@codeaurora.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Pekka Enberg <penberg@kernel.org>
Link: http://lkml.kernel.org/r/20200610163135.17364-7-vbabka@suse.cz


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 8f58119a

mm/slub.c

+13 −3

Original line number	Diff line number	Diff line
		@@ -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))

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