linux-kernel - [PATCH] rcu: refine structure rcu

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Date:   Thu, 18 Jan 2018 18:33:43 +0800
From:   "Liu, Changcheng" <changcheng.liu@...el.com>
To:     Lai Jiangshan <jiangshanlai@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, changcheng.liu@...el.com
Subject: [PATCH] rcu: refine structure rcu_node field for rcu boost

Do not allocate space for rcu boost field when
RCU BOOST is not configured.

Signed-off-by: Liu Changcheng <changcheng.liu@...el.com>

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 46a5d19..88f087e 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -129,6 +129,7 @@ struct rcu_node {
 				/*  if there is no such task.  If there */
 				/*  is no current expedited grace period, */
 				/*  then there can cannot be any such task. */
+#ifdef CONFIG_RCU_BOOST
 	struct list_head *boost_tasks;
 				/* Pointer to first task that needs to be */
 				/*  priority boosted, or NULL if no priority */
@@ -153,6 +154,8 @@ struct rcu_node {
 				/* Number of tasks boosted for expedited GP. */
 	unsigned long n_normal_boosts;
 				/* Number of tasks boosted for normal GP. */
+#endif/* #ifdef CONFIG_RCU_BOOST*/
+
 #ifdef CONFIG_RCU_NOCB_CPU
 	struct swait_queue_head nocb_gp_wq[2];
 				/* Place for rcu_nocb_kthread() to wait GP. */
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index db85ca3..fee0b1e 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -506,8 +506,10 @@ void rcu_read_unlock_special(struct task_struct *t)
 		if (IS_ENABLED(CONFIG_RCU_BOOST)) {
 			/* Snapshot ->boost_mtx ownership w/rnp->lock held. */
 			drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
+#ifdef CONFIG_RCU_BOOST
 			if (&t->rcu_node_entry == rnp->boost_tasks)
 				rnp->boost_tasks = np;
+#endif
 		}
 
 		/*
-- 
2.7.4