diff mbox series

[033/163] mm, slub: introduce static key for slub_debug()

Message ID 20200807061851.QI1qSidy8%akpm@linux-foundation.org
State New
Headers show
Series [001/163] mm/memory.c: avoid access flag update TLB flush for retried page fault | expand

Commit Message

Andrew Morton Aug. 7, 2020, 6:18 a.m. UTC
From: Vlastimil Babka <vbabka@suse.cz>
Subject: 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.

Link: http://lkml.kernel.org/r/20200610163135.17364-7-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Christoph Lameter <cl@linux.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

 mm/slub.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)
diff mbox series


--- a/mm/slub.c~mm-slub-introduce-static-key-for-slub_debug
+++ a/mm/slub.c
@@ -114,13 +114,21 @@ 
  * 			the fast path and disables lockless freelists.
 static inline int kmem_cache_debug(struct kmem_cache *s)
-	return unlikely(s->flags & SLAB_DEBUG_FLAGS);
-	return 0;
+	if (static_branch_unlikely(&slub_debug_enabled))
+		return s->flags & SLAB_DEBUG_FLAGS;
+	return 0;
 void *fixup_red_left(struct kmem_cache *s, void *p)
@@ -1389,6 +1397,8 @@  static int __init setup_slub_debug(char
 		slub_debug_string = saved_str;
+	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))