linux-kernel - [PATCH v1 4/5] kvfree_rcu: Refactor kfree_rcu

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Message-Id: <20210428134422.1894-4-urezki@gmail.com>
Date:   Wed, 28 Apr 2021 15:44:21 +0200
From:   "Uladzislau Rezki (Sony)" <urezki@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>, RCU <rcu@...r.kernel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>
Cc:     Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Axtens <dja@...ens.net>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Uladzislau Rezki <urezki@...il.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: [PATCH v1 4/5] kvfree_rcu: Refactor kfree_rcu_monitor() function

Rearm the monitor work directly from its own function that
is kfree_rcu_monitor(). So this patch puts the invocation
timing control in one place.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
---
 kernel/rcu/tree.c | 35 +++++++++++++++++++++--------------
 1 file changed, 21 insertions(+), 14 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index e44d6f8c56f0..229e909ad437 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3415,37 +3415,44 @@ static inline bool queue_kfree_rcu_work(struct kfree_rcu_cpu *krcp)
 	return !repeat;
 }
 
-static inline void kfree_rcu_drain_unlock(struct kfree_rcu_cpu *krcp,
-					  unsigned long flags)
+/*
+ * This function queues a new batch. If success or nothing to
+ * drain it returns 1. Otherwise 0 is returned indicating that
+ * a reclaim kthread has not processed a previous batch.
+ */
+static inline int kfree_rcu_drain(struct kfree_rcu_cpu *krcp)
 {
+	unsigned long flags;
+	int ret;
+
+	raw_spin_lock_irqsave(&krcp->lock, flags);
+
 	// Attempt to start a new batch.
-	if (queue_kfree_rcu_work(krcp)) {
+	ret = queue_kfree_rcu_work(krcp);
+	if (ret)
 		// Success! Our job is done here.
 		krcp->monitor_todo = false;
-		raw_spin_unlock_irqrestore(&krcp->lock, flags);
-		return;
-	}
 
 	// Previous RCU batch still in progress, try again later.
-	schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
 	raw_spin_unlock_irqrestore(&krcp->lock, flags);
+	return ret;
 }
 
 /*
  * This function is invoked after the KFREE_DRAIN_JIFFIES timeout.
- * It invokes kfree_rcu_drain_unlock() to attempt to start another batch.
+ * It invokes kfree_rcu_drain() to attempt to start another batch.
  */
 static void kfree_rcu_monitor(struct work_struct *work)
 {
-	unsigned long flags;
 	struct kfree_rcu_cpu *krcp = container_of(work, struct kfree_rcu_cpu,
 						 monitor_work.work);
 
-	raw_spin_lock_irqsave(&krcp->lock, flags);
-	if (krcp->monitor_todo)
-		kfree_rcu_drain_unlock(krcp, flags);
-	else
-		raw_spin_unlock_irqrestore(&krcp->lock, flags);
+	if (kfree_rcu_drain(krcp))
+		return;
+
+	// Not success. A previous batch is still in progress.
+	// Rearm a work to repeat an attempt of starting another batch.
+	schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
 }
 
 static enum hrtimer_restart
-- 
2.20.1