slub: Use kmem_cache flags to detect if slab is in debugging mode.

The cacheline with the flags is reachable from the hot paths after the
percpu allocator changes went in. So there is no need anymore to put a
flag into each slab page. Get rid of the SlubDebug flag and use
the flags in kmem_cache instead.

Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

include/linux/page-flags.h

@@ -128,7 +128,6 @@ enum pageflags {
 
 	/* SLUB */
 	PG_slub_frozen = PG_active,
-	PG_slub_debug = PG_error,
 };
 
 #ifndef __GENERATING_BOUNDS_H
@@ -215,7 +214,6 @@ PAGEFLAG(SwapBacked, swapbacked) __CLEARPAGEFLAG(SwapBacked, swapbacked)
 __PAGEFLAG(SlobFree, slob_free)
 
 __PAGEFLAG(SlubFrozen, slub_frozen)
-__PAGEFLAG(SlubDebug, slub_debug)
 
 /*
  * Private page markings that may be used by the filesystem that owns the page

mm/slub.c

@@ -107,11 +107,17 @@
  * 			the fast path and disables lockless freelists.
  */
 
+#define SLAB_DEBUG_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \
+		SLAB_TRACE | SLAB_DEBUG_FREE)
+
+static inline int kmem_cache_debug(struct kmem_cache *s)
+{
 #ifdef CONFIG_SLUB_DEBUG
-#define SLABDEBUG 1
+	return unlikely(s->flags & SLAB_DEBUG_FLAGS);
 #else
-#define SLABDEBUG 0
+	return 0;
 #endif
+}
 
 /*
  * Issues still to be resolved:
@@ -1157,9 +1163,6 @@ static struct page *new_slab(struct kmem_cache *s, gfp_t flags, int node)
 	inc_slabs_node(s, page_to_nid(page), page->objects);
 	page->slab = s;
 	page->flags |= 1 << PG_slab;
-	if (s->flags & (SLAB_DEBUG_FREE | SLAB_RED_ZONE | SLAB_POISON |
-			SLAB_STORE_USER | SLAB_TRACE))
-		__SetPageSlubDebug(page);
 
 	start = page_address(page);
 
@@ -1186,14 +1189,13 @@ static void __free_slab(struct kmem_cache *s, struct page *page)
 	int order = compound_order(page);
 	int pages = 1 << order;
 
-	if (unlikely(SLABDEBUG && PageSlubDebug(page))) {
+	if (kmem_cache_debug(s)) {
 		void *p;
 
 		slab_pad_check(s, page);
 		for_each_object(p, s, page_address(page),
 						page->objects)
 			check_object(s, page, p, 0);
-		__ClearPageSlubDebug(page);
 	}
 
 	kmemcheck_free_shadow(page, compound_order(page));
@@ -1415,8 +1417,7 @@ static void unfreeze_slab(struct kmem_cache *s, struct page *page, int tail)
 			stat(s, tail ? DEACTIVATE_TO_TAIL : DEACTIVATE_TO_HEAD);
 		} else {
 			stat(s, DEACTIVATE_FULL);
-			if (SLABDEBUG && PageSlubDebug(page) &&
-						(s->flags & SLAB_STORE_USER))
+			if (kmem_cache_debug(s) && (s->flags & SLAB_STORE_USER))
 				add_full(n, page);
 		}
 		slab_unlock(page);
@@ -1624,7 +1625,7 @@ load_freelist:
 	object = c->page->freelist;
 	if (unlikely(!object))
 		goto another_slab;
-	if (unlikely(SLABDEBUG && PageSlubDebug(c->page)))
+	if (kmem_cache_debug(s))
 		goto debug;
 
 	c->freelist = get_freepointer(s, object);
@@ -1783,7 +1784,7 @@ static void __slab_free(struct kmem_cache *s, struct page *page,
 	stat(s, FREE_SLOWPATH);
 	slab_lock(page);
 
-	if (unlikely(SLABDEBUG && PageSlubDebug(page)))
+	if (kmem_cache_debug(s))
 		goto debug;
 
 checks_ok:
@@ -3398,16 +3399,6 @@ static void validate_slab_slab(struct kmem_cache *s, struct page *page,
 	} else
 		printk(KERN_INFO "SLUB %s: Skipped busy slab 0x%p\n",
 			s->name, page);
-
-	if (s->flags & DEBUG_DEFAULT_FLAGS) {
-		if (!PageSlubDebug(page))
-			printk(KERN_ERR "SLUB %s: SlubDebug not set "
-				"on slab 0x%p\n", s->name, page);
-	} else {
-		if (PageSlubDebug(page))
-			printk(KERN_ERR "SLUB %s: SlubDebug set on "
-				"slab 0x%p\n", s->name, page);
-	}
 }
 
 static int validate_slab_node(struct kmem_cache *s,