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[PATCH v2 12/17] mm/slab: do not change cache size if debug pagealloc isn't possible

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From: Joonsoo Kim <iamjoonsoo.kim@lge.com>

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@lge.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 mm/slab.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index 9b56685..21aad9d 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2206,10 +2206,17 @@ __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

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[PATCH v2 00/17] mm/slab: introduce new freed objects management way, OBJFREELIST_SLAB js1304@gmail.com - 2016-02-26 07:10 +0100
  [PATCH v2 16/17] mm/slab: introduce new slab management type, OBJFREELIST_SLAB js1304@gmail.com - 2016-02-26 07:10 +0100
    Re: [PATCH v2 16/17] mm/slab: introduce new slab management type,  OBJFREELIST_SLAB Christoph Lameter <cl@linux.com> - 2016-02-26 17:30 +0100
      Re: [PATCH v2 16/17] mm/slab: introduce new slab management type, OBJFREELIST_SLAB Joonsoo Kim <js1304@gmail.com> - 2016-02-26 18:10 +0100
  [PATCH v2 11/17] mm/slab: clean up cache type determination js1304@gmail.com - 2016-02-26 07:10 +0100
  [PATCH v2 03/17] mm/slab: remove the checks for slab implementation bug js1304@gmail.com - 2016-02-26 07:10 +0100
    Re: [PATCH v2 03/17] mm/slab: remove the checks for slab implementation  bug Christoph Lameter <cl@linux.com> - 2016-02-26 17:10 +0100
  [PATCH v2 01/17] mm/slab: fix stale code comment js1304@gmail.com - 2016-02-26 07:10 +0100
  [PATCH v2 04/17] mm/slab: activate debug_pagealloc in SLAB when it is actually enabled js1304@gmail.com - 2016-02-26 07:10 +0100
    Re: [PATCH v2 04/17] mm/slab: activate debug_pagealloc in SLAB when  it is actually enabled Christoph Lameter <cl@linux.com> - 2016-02-26 17:10 +0100
  [PATCH v2 05/17] mm/slab: use more appropriate condition check for debug_pagealloc js1304@gmail.com - 2016-02-26 07:10 +0100
    Re: [PATCH v2 05/17] mm/slab: use more appropriate condition check  for debug_pagealloc Christoph Lameter <cl@linux.com> - 2016-02-26 17:10 +0100
  [PATCH v2 09/17] mm/slab: put the freelist at the end of slab page js1304@gmail.com - 2016-02-26 07:10 +0100
  [PATCH v2 07/17] mm/slab: alternative implementation for DEBUG_SLAB_LEAK js1304@gmail.com - 2016-02-26 07:10 +0100
  [PATCH v2 13/17] mm/slab: make criteria for off slab determination robust and simple js1304@gmail.com - 2016-02-26 07:10 +0100
  [PATCH v2 12/17] mm/slab: do not change cache size if debug pagealloc isn't possible js1304@gmail.com - 2016-02-26 07:10 +0100
    Re: [PATCH v2 12/17] mm/slab: do not change cache size if debug  pagealloc isn't possible Christoph Lameter <cl@linux.com> - 2016-02-26 17:20 +0100
      Re: [PATCH v2 12/17] mm/slab: do not change cache size if debug  pagealloc isn't possible Joonsoo Kim <js1304@gmail.com> - 2016-02-26 18:10 +0100
  [PATCH v2 17/17] mm/slab: avoid returning values by reference js1304@gmail.com - 2016-02-26 07:10 +0100
    Re: [PATCH v2 17/17] mm/slab: avoid returning values by reference Christoph Lameter <cl@linux.com> - 2016-02-26 17:30 +0100
  [PATCH v2 06/17] mm/slab: clean up DEBUG_PAGEALLOC processing code js1304@gmail.com - 2016-02-26 07:10 +0100
  [PATCH v2 08/17] mm/slab: remove object status buffer for DEBUG_SLAB_LEAK js1304@gmail.com - 2016-02-26 07:10 +0100

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