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From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     rcu@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, kernel-team@meta.com,
        rostedt@goodmis.org, hch@lst.de,
        "Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH RFC rcu 06/19] srcu: Move ->srcu_cb_mutex from srcu_struct to srcu_usage
Date:   Thu, 23 Mar 2023 17:19:25 -0700
Message-Id: <20230324001938.3443499-6-paulmck@kernel.org>
In-Reply-To: <3db82572-f156-4a5d-b711-841aa28bd996@paulmck-laptop>
References: <3db82572-f156-4a5d-b711-841aa28bd996@paulmck-laptop>
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This commit moves the ->srcu_cb_mutex field from the srcu_struct structure
to the srcu_usage structure to reduce the size of the former in order
to improve cache locality.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/srcutree.h | 2 +-
 kernel/rcu/srcutree.c    | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index 72fb01fb2eb5..69d49de87b67 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -65,13 +65,13 @@ struct srcu_usage {
 	struct srcu_node *level[RCU_NUM_LVLS + 1];
 						/* First node at each level. */
 	int srcu_size_state;			/* Small-to-big transition state. */
+	struct mutex srcu_cb_mutex;		/* Serialize CB preparation. */
 };
 
 /*
  * Per-SRCU-domain structure, similar in function to rcu_state.
  */
 struct srcu_struct {
-	struct mutex srcu_cb_mutex;		/* Serialize CB preparation. */
 	spinlock_t __private lock;		/* Protect counters and size state. */
 	struct mutex srcu_gp_mutex;		/* Serialize GP work. */
 	unsigned int srcu_idx;			/* Current rdr array element. */
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 2717217de136..6b6d92fe41cf 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -242,7 +242,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
 		return -ENOMEM;
 	ssp->srcu_sup->srcu_size_state = SRCU_SIZE_SMALL;
 	ssp->srcu_sup->node = NULL;
-	mutex_init(&ssp->srcu_cb_mutex);
+	mutex_init(&ssp->srcu_sup->srcu_cb_mutex);
 	mutex_init(&ssp->srcu_gp_mutex);
 	ssp->srcu_idx = 0;
 	ssp->srcu_gp_seq = 0;
@@ -861,7 +861,7 @@ static void srcu_gp_end(struct srcu_struct *ssp)
 	int ss_state;
 
 	/* Prevent more than one additional grace period. */
-	mutex_lock(&ssp->srcu_cb_mutex);
+	mutex_lock(&ssp->srcu_sup->srcu_cb_mutex);
 
 	/* End the current grace period. */
 	spin_lock_irq_rcu_node(ssp);
@@ -921,7 +921,7 @@ static void srcu_gp_end(struct srcu_struct *ssp)
 		}
 
 	/* Callback initiation done, allow grace periods after next. */
-	mutex_unlock(&ssp->srcu_cb_mutex);
+	mutex_unlock(&ssp->srcu_sup->srcu_cb_mutex);
 
 	/* Start a new grace period if needed. */
 	spin_lock_irq_rcu_node(ssp);
-- 
2.40.0.rc2