Re: [Bug #13319] Page allocation failures with b43 and p54usb

[David Rientjes]

On Tue, 30 Jun 2009, Christoph Lameter wrote:

> >   printk(KERN_INFO ": debugging disabled for %s. Use slub_debug=a to "
> >                     "enable it blah blah blah\n");
> >
> > Does that work for you?
> 
> Its definitely better.
> 

I don't see how that's different from enabling debugging on all caches 
like CONFIG_SLAB_DEBUG_ON currently does and then warning at the time of 
slab allocation failure that it may be the result of the debugging 
metadata so the user can subsequently prevent it.  In other words, if we 
use MAX_DEBUG_SIZE as Pekka originally implemented as
(3 * sizeof(void *) + 2 * sizeof(struct track)), do this:

diff --git a/mm/slub.c b/mm/slub.c
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -142,6 +142,11 @@
 				SLAB_POISON | SLAB_STORE_USER)
 
 /*
+ * The maximum amount of metadata added to a slab when debugging is enabled.
+ */
+#define MAX_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 | \
@@ -1561,6 +1566,21 @@ slab_out_of_memory(struct kmem_cache *s, gfp_t gfpflags, int nid)
 		"default order: %d, min order: %d\n", s->name, s->objsize,
 		s->size, oo_order(s->oo), oo_order(s->min));
 
+	if (s->flags & (SLAB_POISON | SLAB_RED_ZONE | SLAB_STORE_USER)) {
+		int min_order;
+
+		/*
+		 * Debugging is enabled, which may increase oo_order(s->min), so
+		 * warn the user that allocation failures may be avoided if
+		 * debugging is enabled for this cache.
+		 */
+		min_order = get_order(s->size - MAX_DEBUG_SIZE);
+		if (min_order < oo_order(s->min))
+			printk(KERN_WARNING "  %s debugging increased min order "
+			       "from %d to %d, use slab_debug=-,%s to disable.",
+			       s->name, min_order, oo_order(s->min), s->name);
+	}
+
 	for_each_online_node(node) {
 		struct kmem_cache_node *n = get_node(s, node);
 		unsigned long nr_slabs;
--
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