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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 04/19] srcu: Move ->level from srcu_struct to srcu_usage
Date:   Thu, 23 Mar 2023 17:19:23 -0700
Message-Id: <20230324001938.3443499-4-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 ->level[] array 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 |  4 ++--
 kernel/rcu/srcutree.c    | 14 +++++++-------
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index 2689e64024bb..362c8f39c53d 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -62,14 +62,14 @@ struct srcu_node {
  */
 struct srcu_usage {
 	struct srcu_node *node;			/* Combining tree. */
+	struct srcu_node *level[RCU_NUM_LVLS + 1];
+						/* First node at each level. */
 };
 
 /*
  * Per-SRCU-domain structure, similar in function to rcu_state.
  */
 struct srcu_struct {
-	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. */
 	spinlock_t __private lock;		/* Protect counters and size state. */
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index ad1d5ca42a99..90d753e10e33 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -178,9 +178,9 @@ static bool init_srcu_struct_nodes(struct srcu_struct *ssp, gfp_t gfp_flags)
 		return false;
 
 	/* Work out the overall tree geometry. */
-	ssp->level[0] = &ssp->srcu_sup->node[0];
+	ssp->srcu_sup->level[0] = &ssp->srcu_sup->node[0];
 	for (i = 1; i < rcu_num_lvls; i++)
-		ssp->level[i] = ssp->level[i - 1] + num_rcu_lvl[i - 1];
+		ssp->srcu_sup->level[i] = ssp->srcu_sup->level[i - 1] + num_rcu_lvl[i - 1];
 	rcu_init_levelspread(levelspread, num_rcu_lvl);
 
 	/* Each pass through this loop initializes one srcu_node structure. */
@@ -202,10 +202,10 @@ static bool init_srcu_struct_nodes(struct srcu_struct *ssp, gfp_t gfp_flags)
 		}
 
 		/* Non-root node. */
-		if (snp == ssp->level[level + 1])
+		if (snp == ssp->srcu_sup->level[level + 1])
 			level++;
-		snp->srcu_parent = ssp->level[level - 1] +
-				   (snp - ssp->level[level]) /
+		snp->srcu_parent = ssp->srcu_sup->level[level - 1] +
+				   (snp - ssp->srcu_sup->level[level]) /
 				   levelspread[level - 1];
 	}
 
@@ -214,7 +214,7 @@ static bool init_srcu_struct_nodes(struct srcu_struct *ssp, gfp_t gfp_flags)
 	 * leaves of the srcu_node tree.
 	 */
 	level = rcu_num_lvls - 1;
-	snp_first = ssp->level[level];
+	snp_first = ssp->srcu_sup->level[level];
 	for_each_possible_cpu(cpu) {
 		sdp = per_cpu_ptr(ssp->sda, cpu);
 		sdp->mynode = &snp_first[cpu / levelspread[level]];
@@ -889,7 +889,7 @@ static void srcu_gp_end(struct srcu_struct *ssp)
 		srcu_for_each_node_breadth_first(ssp, snp) {
 			spin_lock_irq_rcu_node(snp);
 			cbs = false;
-			last_lvl = snp >= ssp->level[rcu_num_lvls - 1];
+			last_lvl = snp >= ssp->srcu_sup->level[rcu_num_lvls - 1];
 			if (last_lvl)
 				cbs = ss_state < SRCU_SIZE_BIG || snp->srcu_have_cbs[idx] == gpseq;
 			snp->srcu_have_cbs[idx] = gpseq;
-- 
2.40.0.rc2