linux-kernel - [PATCH 4.9 57/71] rhashtable: reorganize struct rhashtable layout

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Message-Id: <20181016170542.218605806@linuxfoundation.org>
Date:   Tue, 16 Oct 2018 19:09:54 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.9 57/71] rhashtable: reorganize struct rhashtable layout

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@...gle.com>

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@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
(cherry picked from commit e5d672a0780d9e7118caad4c171ec88b8299398d)
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 include/linux/rhashtable.h |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- 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;
 };
 
 /**