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[PATCH tip/core/rcu 07/12] rcu: Limit rcu_capacity[] size to RCU_NUM_LVLS items

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From: Alexander Gordeev <agordeev@redhat.com>

Number of items in rcu_capacity[] array is defined by macro
MAX_RCU_LVLS. However, that array is never accessed beyond
RCU_NUM_LVLS index. Therefore, we can limit the array to
RCU_NUM_LVLS items and eliminate MAX_RCU_LVLS. As result,
in most cases the memory is conserved.

Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 12 ++++++------
 kernel/rcu/tree.h |  2 --
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 2103beedb49f..2ec7b796f660 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3998,19 +3998,19 @@ static void __init rcu_init_one(struct rcu_state *rsp,
 		"rcu_node_0",
 		"rcu_node_1",
 		"rcu_node_2",
-		"rcu_node_3" };  /* Match MAX_RCU_LVLS */
+		"rcu_node_3" };
 	static const char * const fqs[] = {
 		"rcu_node_fqs_0",
 		"rcu_node_fqs_1",
 		"rcu_node_fqs_2",
-		"rcu_node_fqs_3" };  /* Match MAX_RCU_LVLS */
+		"rcu_node_fqs_3" };
 	static u8 fl_mask = 0x1;
 	int cpustride = 1;
 	int i;
 	int j;
 	struct rcu_node *rnp;
 
-	BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */
+	BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */
 
 	/* Silence gcc 4.8 false positive about array index out of range. */
 	if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
@@ -4082,7 +4082,7 @@ static void __init rcu_init_geometry(void)
 {
 	ulong d;
 	int i;
-	int rcu_capacity[MAX_RCU_LVLS];
+	int rcu_capacity[RCU_NUM_LVLS];
 
 	/*
 	 * Initialize any unspecified boot parameters.
@@ -4122,14 +4122,14 @@ static void __init rcu_init_geometry(void)
 	 * with the given number of levels.
 	 */
 	rcu_capacity[0] = rcu_fanout_leaf;
-	for (i = 1; i < MAX_RCU_LVLS; i++)
+	for (i = 1; i < RCU_NUM_LVLS; i++)
 		rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
 
 	/*
 	 * The tree must be able to accommodate the configured number of CPUs.
 	 * If this limit is exceeded than we have a serious problem elsewhere.
 	 */
-	if (nr_cpu_ids > rcu_capacity[MAX_RCU_LVLS - 1])
+	if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1])
 		panic("rcu_init_geometry: rcu_capacity[] is too small");
 
 	/* Calculate the number of levels in the tree. */
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index a6faae53ea8f..d625e9ff0faf 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -36,8 +36,6 @@
  * Of course, your mileage may vary.
  */
 
-#define MAX_RCU_LVLS 4
-
 #ifdef CONFIG_RCU_FANOUT
 #define RCU_FANOUT CONFIG_RCU_FANOUT
 #else /* #ifdef CONFIG_RCU_FANOUT */
-- 
1.8.1.5

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Thread

[PATCH tip/core/rcu 0/12] Tree geometry-initialization  simplifications for 4.3 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 03/12] rcu: Remove superfluous local variable in rcu_init_geometry() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 08/12] rcu: Remove unnecessary fields from rcu_state structure "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 12/12] rcu: Reset rcu_fanout_leaf if out of bounds "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 11/12] rcu: Shut up bogus gcc array bounds warning "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 10/12] rcu: Simplify arithmetic to calculate number of RCU nodes "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 05/12] rcu: Simplify rcu_init_geometry() capacity arithmetics "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 09/12] rcu: Limit count of static data to the number of RCU levels "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 01/12] rcu: Provide more diagnostics for stalled GP kthread "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
    [PATCH tip/core/rcu 04/12] rcu: Cleanup rcu_init_geometry() code and arithmetics "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
    [PATCH tip/core/rcu 02/12] rcu: Panic if RCU tree can not accommodate all CPUs "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
    [PATCH tip/core/rcu 07/12] rcu: Limit rcu_capacity[] size to RCU_NUM_LVLS items "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
    [PATCH tip/core/rcu 06/12] rcu: Limit rcu_state::levelcnt[] to RCU_NUM_LVLS items "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200

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