linux-kernel - [PATCH 1/2] rcu/kvfree: Remove useless monitor

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Date:   Thu,  2 Jun 2022 10:06:43 +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:     Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <neeraj.iitr10@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: [PATCH 1/2] rcu/kvfree: Remove useless monitor_todo flag

From: "Joel Fernandes (Google)" <joel@...lfernandes.org>

monitor_todo is not needed as the work struct already tracks
if work is pending. Just use that to know if work is pending
using schedule_delayed_work() helper.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
 kernel/rcu/tree.c | 33 ++++++++++++++++-----------------
 1 file changed, 16 insertions(+), 17 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 222d59299a2a..fd16c0b46d9e 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3295,7 +3295,6 @@ struct kfree_rcu_cpu_work {
  * @krw_arr: Array of batches of kfree_rcu() objects waiting for a grace period
  * @lock: Synchronize access to this structure
  * @monitor_work: Promote @head to @head_free after KFREE_DRAIN_JIFFIES
- * @monitor_todo: Tracks whether a @monitor_work delayed work is pending
  * @initialized: The @rcu_work fields have been initialized
  * @count: Number of objects for which GP not started
  * @bkvcache:
@@ -3320,7 +3319,6 @@ struct kfree_rcu_cpu {
 	struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES];
 	raw_spinlock_t lock;
 	struct delayed_work monitor_work;
-	bool monitor_todo;
 	bool initialized;
 	int count;
 
@@ -3500,6 +3498,18 @@ static void kfree_rcu_work(struct work_struct *work)
 	}
 }
 
+static bool
+need_offload_krc(struct kfree_rcu_cpu *krcp)
+{
+	int i;
+
+	for (i = 0; i < FREE_N_CHANNELS; i++)
+		if (krcp->bkvhead[i])
+			return true;
+
+	return !!krcp->head;
+}
+
 /*
  * This function is invoked after the KFREE_DRAIN_JIFFIES timeout.
  */
@@ -3556,9 +3566,7 @@ static void kfree_rcu_monitor(struct work_struct *work)
 	// of the channels that is still busy we should rearm the
 	// work to repeat an attempt. Because previous batches are
 	// still in progress.
-	if (!krcp->bkvhead[0] && !krcp->bkvhead[1] && !krcp->head)
-		krcp->monitor_todo = false;
-	else
+	if (need_offload_krc(krcp))
 		schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
 
 	raw_spin_unlock_irqrestore(&krcp->lock, flags);
@@ -3746,11 +3754,8 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
 	WRITE_ONCE(krcp->count, krcp->count + 1);
 
 	// Set timer to drain after KFREE_DRAIN_JIFFIES.
-	if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING &&
-	    !krcp->monitor_todo) {
-		krcp->monitor_todo = true;
+	if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING)
 		schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
-	}
 
 unlock_return:
 	krc_this_cpu_unlock(krcp, flags);
@@ -3825,14 +3830,8 @@ void __init kfree_rcu_scheduler_running(void)
 		struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
 
 		raw_spin_lock_irqsave(&krcp->lock, flags);
-		if ((!krcp->bkvhead[0] && !krcp->bkvhead[1] && !krcp->head) ||
-				krcp->monitor_todo) {
-			raw_spin_unlock_irqrestore(&krcp->lock, flags);
-			continue;
-		}
-		krcp->monitor_todo = true;
-		schedule_delayed_work_on(cpu, &krcp->monitor_work,
-					 KFREE_DRAIN_JIFFIES);
+		if (need_offload_krc(krcp))
+			schedule_delayed_work_on(cpu, &krcp->monitor_work, KFREE_DRAIN_JIFFIES);
 		raw_spin_unlock_irqrestore(&krcp->lock, flags);
 	}
 }
-- 
2.30.2