[PATCH RFC rcu 09/19] srcu: Move ->srcu_gp_mutex from srcu_struct to srcu_usage

["Paul E. McKenney" <paulmck@xxxxxxxxxx>]

This commit moves the ->srcu_gp_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@xxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 include/linux/srcutree.h |  2 +-
 kernel/rcu/srcutree.c    | 14 +++++++-------
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index 6fe5743c1179..6402cd5a93ef 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -67,13 +67,13 @@ struct srcu_usage {
 	int srcu_size_state;			/* Small-to-big transition state. */
 	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. */
 };
 
 /*
  * Per-SRCU-domain structure, similar in function to rcu_state.
  */
 struct srcu_struct {
-	struct mutex srcu_gp_mutex;		/* Serialize GP work. */
 	unsigned int srcu_idx;			/* Current rdr array element. */
 	unsigned long srcu_gp_seq;		/* Grace-period seq #. */
 	unsigned long srcu_gp_seq_needed;	/* Latest gp_seq needed. */
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 579c43ff0f4b..3bf3408c7716 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -245,7 +245,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
 	ssp->srcu_sup->srcu_size_state = SRCU_SIZE_SMALL;
 	ssp->srcu_sup->node = NULL;
 	mutex_init(&ssp->srcu_sup->srcu_cb_mutex);
-	mutex_init(&ssp->srcu_gp_mutex);
+	mutex_init(&ssp->srcu_sup->srcu_gp_mutex);
 	ssp->srcu_idx = 0;
 	ssp->srcu_gp_seq = 0;
 	ssp->srcu_barrier_seq = 0;
@@ -876,7 +876,7 @@ static void srcu_gp_end(struct srcu_struct *ssp)
 	if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, gpseq))
 		WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, gpseq);
 	spin_unlock_irq_rcu_node(ssp->srcu_sup);
-	mutex_unlock(&ssp->srcu_gp_mutex);
+	mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
 	/* A new grace period can start at this point.  But only one. */
 
 	/* Initiate callback invocation as needed. */
@@ -1607,7 +1607,7 @@ static void srcu_advance_state(struct srcu_struct *ssp)
 {
 	int idx;
 
-	mutex_lock(&ssp->srcu_gp_mutex);
+	mutex_lock(&ssp->srcu_sup->srcu_gp_mutex);
 
 	/*
 	 * Because readers might be delayed for an extended period after
@@ -1625,7 +1625,7 @@ static void srcu_advance_state(struct srcu_struct *ssp)
 		if (ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed)) {
 			WARN_ON_ONCE(rcu_seq_state(ssp->srcu_gp_seq));
 			spin_unlock_irq_rcu_node(ssp->srcu_sup);
-			mutex_unlock(&ssp->srcu_gp_mutex);
+			mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
 			return;
 		}
 		idx = rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq));
@@ -1633,7 +1633,7 @@ static void srcu_advance_state(struct srcu_struct *ssp)
 			srcu_gp_start(ssp);
 		spin_unlock_irq_rcu_node(ssp->srcu_sup);
 		if (idx != SRCU_STATE_IDLE) {
-			mutex_unlock(&ssp->srcu_gp_mutex);
+			mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
 			return; /* Someone else started the grace period. */
 		}
 	}
@@ -1641,7 +1641,7 @@ static void srcu_advance_state(struct srcu_struct *ssp)
 	if (rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) == SRCU_STATE_SCAN1) {
 		idx = 1 ^ (ssp->srcu_idx & 1);
 		if (!try_check_zero(ssp, idx, 1)) {
-			mutex_unlock(&ssp->srcu_gp_mutex);
+			mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
 			return; /* readers present, retry later. */
 		}
 		srcu_flip(ssp);
@@ -1659,7 +1659,7 @@ static void srcu_advance_state(struct srcu_struct *ssp)
 		 */
 		idx = 1 ^ (ssp->srcu_idx & 1);
 		if (!try_check_zero(ssp, idx, 2)) {
-			mutex_unlock(&ssp->srcu_gp_mutex);
+			mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
 			return; /* readers present, retry later. */
 		}
 		ssp->srcu_n_exp_nodelay = 0;
-- 
2.40.0.rc2