Commit a6a82ce1 authored by Joel Fernandes (Google)'s avatar Joel Fernandes (Google) Committed by Paul E. McKenney
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rcu/tree: Count number of batched kfree_rcu() locklessly 



We can relax the correctness of counting of number of queued objects in
favor of not hurting performance, by locklessly sampling per-cpu
counters. This should be Ok since under high memory pressure, it should not
matter if we are off by a few objects while counting. The shrinker will
still do the reclaim.

Signed-off-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
[ paulmck: Remove unused "flags" variable. ]
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 9154244c

kernel/rcu/tree.c

+4 −6
Original line number Diff line number Diff line
@@ -2939,7 +2939,7 @@ static inline bool queue_kfree_rcu_work(struct kfree_rcu_cpu *krcp) 
				krcp->head = NULL;

			}



			krcp->count = 0;

			WRITE_ONCE(krcp->count, 0);



			/*

			 * One work is per one batch, so there are two "free channels",
@@ -3077,7 +3077,7 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func) 
		krcp->head = head;

	}



	krcp->count++;

	WRITE_ONCE(krcp->count, krcp->count + 1);



	// Set timer to drain after KFREE_DRAIN_JIFFIES.

	if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING &&
@@ -3097,15 +3097,13 @@ static unsigned long 
kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc)

{

	int cpu;

	unsigned long flags, count = 0;

	unsigned long count = 0;



	/* Snapshot count of all CPUs */

	for_each_online_cpu(cpu) {

		struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);



		spin_lock_irqsave(&krcp->lock, flags);

		count += krcp->count;

		spin_unlock_irqrestore(&krcp->lock, flags);

		count += READ_ONCE(krcp->count);

	}



	return count;