[Devel] [PATCH rh7 v2 4/4] mm/slub: set slub_max_order = 0 by default.

[Andrey Ryabinin]

Setting slub_max_order to 0 makes slub to use minimum possible
order for slub page.

Pros:
 - Less fragmentation of slab objects in slab pages -> less slab
    consumption. E.g. on dvd-store test on machine with 256G this
     saves us ~3G.
 - Potentially faster in high memory fragmentation cases (we don't attempt
    to allocate higher-than-necessary-order page).

Cons:
 - Potentially slower if higher-order page available in the system
    (less __alloc_pages() calls).
 - May increase memory waste for kmem_caches of certain size
    (e.g. with 1025-byte objects we waste 1022 bytes per 4096 bytes if
    slub order is zero. But with slub order 3 and 1025-byte objects
    we waste only 993-bytes per 32768 bytes => 124 bytes per 4096)

According to dvd-store test pros of this change is outweigh the cons.

https://jira.sw.ru/browse/PSBM-83199
Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/slub.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/slub.c b/mm/slub.c
index de39b176c995..1fb70dcb6d82 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2989,7 +2989,7 @@ EXPORT_SYMBOL(kmem_cache_alloc_bulk);
  * take the list_lock.
  */
 static int slub_min_order;
-static int slub_max_order = PAGE_ALLOC_COSTLY_ORDER;
+static int slub_max_order;
 static int slub_min_objects;
 
 /*
-- 
2.19.2