slub: Deal with hyperthetical case of PAGE_SIZE > 2M

kmalloc_index() currently returns -1 if the PAGE_SIZE is larger than 2M
which seems to cause some concern since the callers do not check for -1.

Insert a BUG() and add a comment to the -1 explaining that the code
cannot be reached.

Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index ca0c076b2374..c8668d161dd8 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -177,7 +177,8 @@ static __always_inline int kmalloc_index(size_t size)
         if (size <=   4 * 1024) return 12;
 /*
  * The following is only needed to support architectures with a larger page
- * size than 4k.
+ * size than 4k. We need to support 2 * PAGE_SIZE here. So for a 64k page
+ * size we would have to go up to 128k.
  */
         if (size <=   8 * 1024) return 13;
         if (size <=  16 * 1024) return 14;
@@ -188,7 +189,8 @@ static __always_inline int kmalloc_index(size_t size)
         if (size <= 512 * 1024) return 19;
         if (size <= 1024 * 1024) return 20;
         if (size <=  2 * 1024 * 1024) return 21;
-        return -1;
+        BUG();
+        return -1; /* Will never be reached */
 
 /*
  * What we really wanted to do and cannot do because of compiler issues is: