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From: Christoph Lameter on 3 Aug 2010 23:00
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(a)google.com>
Signed-off-by: Christoph Lameter <cl(a)linux-foundation.org>

---
include/linux/page-flags.h | 2 --
mm/slub.c | 33 ++++++++++++---------------------
2 files changed, 12 insertions(+), 23 deletions(-)

Index: linux-2.6/include/linux/page-flags.h
===================================================================
--- linux-2.6.orig/include/linux/page-flags.h 2010-07-28 12:03:19.000000000 -0500
+++ linux-2.6/include/linux/page-flags.h 2010-07-28 12:44:57.000000000 -0500
@@ -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) __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 2010-07-28 12:44:56.000000000 -0500
+++ linux-2.6/mm/slub.c 2010-07-28 12:44:57.000000000 -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:
@@ -3398,16 +3399,6 @@ 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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Prev: [S+Q3 20/23] slub: Shared cache to exploit cross cpu caching abilities.
Next: [S+Q3 12/23] slub: Extract hooks for memory checkers from hotpaths