[PATCH 12/16] mm/slab: do not change cache size if debug pagealloc isn't possible

[Joonsoo Kim]

We can fail to setup off slab in some conditions. Even in this case,
debug pagealloc increases cache size to PAGE_SIZE in advance and
it is waste because debug pagealloc cannot work for it when it isn't
the off slab. To improve this situation, this patch checks first
that this cache with increased size is suitable for off slab.
It actually increases cache size when it is suitable for off-slab,
so possible waste is removed.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
---
 mm/slab.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index 7a253a9..b0f6eda 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2207,10 +2207,17 @@ __kmem_cache_create (struct kmem_cache *cachep, unsigned long flags)
 	 */
 	if (debug_pagealloc_enabled() && (flags & SLAB_POISON) &&
 		!slab_early_init && size >= kmalloc_size(INDEX_NODE) &&
-		size >= 256 && cachep->object_size > cache_line_size() &&
-		size < PAGE_SIZE) {
-		cachep->obj_offset += PAGE_SIZE - size;
-		size = PAGE_SIZE;
+		size >= 256 && cachep->object_size > cache_line_size()) {
+		if (size < PAGE_SIZE || size % PAGE_SIZE == 0) {
+			size_t tmp_size = ALIGN(size, PAGE_SIZE);
+
+			if (set_off_slab_cache(cachep, tmp_size, flags)) {
+				flags |= CFLGS_OFF_SLAB;
+				cachep->obj_offset += tmp_size - size;
+				size = tmp_size;
+				goto done;
+			}
+		}
 	}
 #endif
 
-- 
1.9.1