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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: Joel Fernandes (Google) <joel@joelfernandes.org>
[ paulmck: Remove unused "flags" variable. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Joel Fernandes (Google) 2020-03-16 12:32:28 -04:00 committed by Paul E. McKenney
parent 9154244c1a
commit a6a82ce18b
1 changed files with 4 additions and 6 deletions
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10
kernel/rcu/tree.c
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@ -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;