rhashtable: kill ht->shift atomic operations

Commit c0c09bfdc415 ("rhashtable: avoid unnecessary wakeup for worker
queue") changed ht->shift to be atomic, which is actually unnecessary.

Instead of leaving the current shift in the core rhashtable structure,
it can be cached inside the individual bucket tables.

There, it will only be initialized once during a new table allocation
in the shrink/expansion slow path, and from then onward it stays immutable
for the rest of the bucket table liftime.

That allows shift to be non-atomic. The patch also moves hash_rnd
management into the table setup. The rhashtable structure now consumes
3 instead of 4 cachelines.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Ying Xue <ying.xue@windriver.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 3 deletions

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 5ef8ea551556..c93ff8ac474a 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -50,6 +50,7 @@ struct rhash_head {
  * struct bucket_table - Table of hash buckets
  * @size: Number of hash buckets
  * @hash_rnd: Random seed to fold into hash
+ * @shift: Current size (1 << shift)
  * @locks_mask: Mask to apply before accessing locks[]
  * @locks: Array of spinlocks protecting individual buckets
  * @buckets: size * hash buckets
@@ -57,6 +58,7 @@ struct rhash_head {
 struct bucket_table {
 	size_t			size;
 	u32			hash_rnd;
+	u32			shift;
 	unsigned int		locks_mask;
 	spinlock_t		*locks;
 
@@ -99,7 +101,6 @@ struct rhashtable_params {
  * @tbl: Bucket table
  * @future_tbl: Table under construction during expansion/shrinking
  * @nelems: Number of elements in table
- * @shift: Current size (1 << shift)
  * @p: Configuration parameters
  * @run_work: Deferred worker to expand/shrink asynchronously
  * @mutex: Mutex to protect current/future table swapping
@@ -110,12 +111,11 @@ struct rhashtable {
 	struct bucket_table __rcu	*tbl;
 	struct bucket_table __rcu       *future_tbl;
 	atomic_t			nelems;
-	atomic_t			shift;
+	bool                            being_destroyed;
 	struct rhashtable_params	p;
 	struct work_struct		run_work;
 	struct mutex                    mutex;
 	struct list_head		walkers;
-	bool                            being_destroyed;
 };
 
 /**