[patch] slub: use size and objsize orders to disable debug flags

David Rientjes
2009-07-28T01:30:48Z

This patch moves the masking of debugging flags which increase a cache's
min order due to metadata when `slub_debug=O' is used from
kmem_cache_flags() to kmem_cache_open().

Instead of defining the maximum metadata size increase in a preprocessor
macro, this approach uses the cache's ->size and ->objsize members to
determine if the min order increased due to debugging options. If so,
the flags specified in the more appropriately named DEBUG_METADATA_FLAGS
are masked off.

This approach was suggested by Christoph Lameter
<cl@linux-foundation.org>.

Cc: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: David Rientjes <rientjes@google.com>
---
mm/slub.c | 40 +++++++++++++++++++---------------------
1 files changed, 19 insertions(+), 21 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -142,11 +142,11 @@
SLAB_POISON | SLAB_STORE_USER)

/*
- * Debugging flags that require metadata to be stored in the slab, up to
- * DEBUG_SIZE in size.
+ * Debugging flags that require metadata to be stored in the slab. These get
+ * disabled when slub_debug=O is used and a cache's min order increases with
+ * metadata.
*/
-#define DEBUG_SIZE_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER)
-#define DEBUG_SIZE (3 * sizeof(void *) + 2 * sizeof(struct track))
+#define DEBUG_METADATA_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER)

/*
* Set of flags that will prevent slab merging
@@ -1040,27 +1040,13 @@ static unsigned long kmem_cache_flags(unsigned long objsize,
unsigned long flags, const char *name,
void (*ctor)(void *))
{
- int debug_flags = slub_debug;
-
/*
* Enable debugging if selected on the kernel commandline.
*/
- if (debug_flags) {
- if (slub_debug_slabs &&
- strncmp(slub_debug_slabs, name, strlen(slub_debug_slabs)))
- goto out;
-
- /*
- * Disable debugging that increases slab size if the minimum
- * slab order would have increased as a result.
- */
- if (disable_higher_order_debug &&
- get_order(objsize + DEBUG_SIZE) > get_order(objsize))
- debug_flags &= ~DEBUG_SIZE_FLAGS;
+ if (slub_debug && (!slub_debug_slabs ||
+ !strncmp(slub_debug_slabs, name, strlen(slub_debug_slabs))))
+ flags |= slub_debug;

- flags |= debug_flags;
- }
-out:
return flags;
}
#else
@@ -2488,6 +2474,18 @@ static int kmem_cache_open(struct kmem_cache *s, gfp_t gfpflags,

if (!calculate_sizes(s, -1))
goto error;
+ if (disable_higher_order_debug) {
+ /*
+ * Disable debugging flags that store metadata if the min slab
+ * order increased.
+ */
+ if (get_order(s->size) > get_order(s->objsize)) {
+ s->flags &= ~DEBUG_METADATA_FLAGS;
+ s->offset = 0;
+ if (!calculate_sizes(s, -1))
+ goto error;
+ }
+ }

/*
* The larger the object size is, the more pages we want on the partial