rhashtable: reorganize struct rhashtable layout

While under frags DDOS I noticed unfortunate false sharing between
@nelems and @params.automatic_shrinking

Move @nelems at the end of struct rhashtable so that first cache line
is shared between all cpus, because almost never dirtied.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit e5d672a0780d9e7118caad4c171ec88b8299398d)
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 85d1ffc..4421e5c 100644 (file)
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -138,7 +138,6 @@ struct rhashtable_params {
 /**
  * struct rhashtable - Hash table handle
  * @tbl: Bucket table
- * @nelems: Number of elements in table
  * @key_len: Key length for hashfn
  * @elasticity: Maximum chain length before rehash
  * @p: Configuration parameters
@@ -146,10 +145,10 @@ struct rhashtable_params {
  * @run_work: Deferred worker to expand/shrink asynchronously
  * @mutex: Mutex to protect current/future table swapping
  * @lock: Spin lock to protect walker list
+ * @nelems: Number of elements in table
  */
 struct rhashtable {
        struct bucket_table __rcu       *tbl;
-       atomic_t                        nelems;
        unsigned int                    key_len;
        unsigned int                    elasticity;
        struct rhashtable_params        p;
@@ -157,6 +156,7 @@ struct rhashtable {
        struct work_struct              run_work;
        struct mutex                    mutex;
        spinlock_t                      lock;
+       atomic_t                        nelems;
 };
 
 /**