slub: add option to disable higher order debugging slabs
When debugging is enabled, slub requires that additional metadata be
stored in slabs for certain options: SLAB_RED_ZONE, SLAB_POISON, and
SLAB_STORE_USER.
Consequently, it may require that the minimum possible slab order needed
to allocate a single object be greater when using these options. The
most notable example is for objects that are PAGE_SIZE bytes in size.
Higher minimum slab orders may cause page allocation failures when oom or
under heavy fragmentation.
This patch adds a new slub_debug option, which disables debugging by
default for caches that would have resulted in higher minimum orders:
slub_debug=O
When this option is used on systems with 4K pages, kmalloc-4096, for
example, will not have debugging enabled by default even if
CONFIG_SLUB_DEBUG_ON is defined because it would have resulted in a
order-1 minimum slab order.
Reported-by: Larry Finger <Larry.Finger@lwfinger.net>
Tested-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
diff --git a/mm/slub.c b/mm/slub.c
index a9201d8..466089c 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -142,6 +142,13 @@
SLAB_POISON | SLAB_STORE_USER)
/*
+ * Debugging flags that require metadata to be stored in the slab, up to
+ * DEBUG_SIZE in size.
+ */
+#define DEBUG_SIZE_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER)
+#define DEBUG_SIZE (3 * sizeof(void *) + 2 * sizeof(struct track))
+
+/*
* Set of flags that will prevent slab merging
*/
#define SLUB_NEVER_MERGE (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \
@@ -326,6 +333,7 @@
#endif
static char *slub_debug_slabs;
+static int disable_higher_order_debug;
/*
* Object debugging
@@ -977,6 +985,15 @@
*/
goto check_slabs;
+ if (tolower(*str) == 'o') {
+ /*
+ * Avoid enabling debugging on caches if its minimum order
+ * would increase as a result.
+ */
+ disable_higher_order_debug = 1;
+ goto out;
+ }
+
slub_debug = 0;
if (*str == '-')
/*
@@ -1023,13 +1040,27 @@
unsigned long flags, const char *name,
void (*ctor)(void *))
{
+ int debug_flags = slub_debug;
+
/*
* Enable debugging if selected on the kernel commandline.
*/
- if (slub_debug && (!slub_debug_slabs ||
- strncmp(slub_debug_slabs, name, strlen(slub_debug_slabs)) == 0))
- flags |= slub_debug;
+ 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;
+
+ flags |= debug_flags;
+ }
+out:
return flags;
}
#else
@@ -1561,6 +1592,10 @@
"default order: %d, min order: %d\n", s->name, s->objsize,
s->size, oo_order(s->oo), oo_order(s->min));
+ if (oo_order(s->min) > get_order(s->objsize))
+ printk(KERN_WARNING " %s debugging increased min order, use "
+ "slub_debug=O to disable.\n", s->name);
+
for_each_online_node(node) {
struct kmem_cache_node *n = get_node(s, node);
unsigned long nr_slabs;