slab: document kmalloc_order

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/slab_common.c

@@ -582,6 +582,11 @@ void __init create_kmalloc_caches(unsigned long flags)
 }
 #endif /* !CONFIG_SLOB */
 
+/*
+ * To avoid unnecessary overhead, we pass through large allocation requests
+ * directly to the page allocator. We use __GFP_COMP, because we will need to
+ * know the allocation order to free the pages properly in kfree.
+ */
 void *kmalloc_order(size_t size, gfp_t flags, unsigned int order)
 {
 	void *ret;