[PATCH 2/3] slub: reduce failure of this_cpu_cmpxchg in put_cpu_partial() after unfreezing

[Joonsoo Kim <js1304@gmail.com>]

In current implementation, after unfreezing, we doesn't touch oldpage,
so it remain 'NOT NULL'. When we call this_cpu_cmpxchg()
with this old oldpage, this_cpu_cmpxchg() is mostly be failed.

We can change value of oldpage to NULL after unfreezing,
because unfreeze_partial() ensure that all the cpu partial slabs is removed
from cpu partial list. In this time, we could expect that
this_cpu_cmpxchg is mostly succeed.

Signed-off-by: Joonsoo Kim <js1304@gmail.com>

diff --git a/mm/slub.c b/mm/slub.c
index 92f1c0e..531d8ed 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1968,6 +1968,7 @@ int put_cpu_partial(struct kmem_cache *s, struct page *page, int drain)
 				local_irq_save(flags);
 				unfreeze_partials(s);
 				local_irq_restore(flags);
+				oldpage = NULL;
 				pobjects = 0;
 				pages = 0;
 				stat(s, CPU_PARTIAL_DRAIN);
-- 
1.7.9.5

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