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

[Christoph Lameter <cl@linux-foundation.org>]

Subject: 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.

Signed-off-by: Christoph Lameter <cl@linux-foundation.org>

---
 include/linux/page-flags.h |    1 -
 mm/slub.c                  |   33 ++++++++++++---------------------
 2 files changed, 12 insertions(+), 22 deletions(-)

Index: linux-2.6/include/linux/page-flags.h
===================================================================
--- linux-2.6.orig/include/linux/page-flags.h	2010-05-28 11:37:33.000000000 -0500
+++ linux-2.6/include/linux/page-flags.h	2010-06-01 08:58:50.000000000 -0500
@@ -215,7 +215,6 @@ PAGEFLAG(SwapBacked, swapbacked) __CLEAR
 __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
Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2010-06-01 08:58:49.000000000 -0500
+++ linux-2.6/mm/slub.c	2010-06-01 08:58:50.000000000 -0500
@@ -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
 	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_cach
 	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_ca
 			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_cach
 	stat(s, FREE_SLOWPATH);
 	slab_lock(page);

-	if (unlikely(SLABDEBUG && PageSlubDebug(page)))
+	if (kmem_cache_debug(s))
 		goto debug;

 checks_ok:
@@ -3395,16 +3396,6 @@ static void validate_slab_slab(struct km
 	} 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,

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