The following commit has been merged into the core/rcu branch of tip:
Commit-ID: a6a82ce18ba443186545d3fefbee8b9419a859dc
Gitweb:
https://git.kernel.org/tip/a6a82ce18ba443186545d3fefbee8b9419a859dc
Author: Joel Fernandes (Google) <j...@joelfernandes.org>
AuthorDate: Mon, 16 Mar 2020 12:32:28 -04:00
Committer: Paul E. McKenney <paul...@kernel.org>
CommitterDate: Mon, 27 Apr 2020 11:02:50 -07:00
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) <j...@joelfernandes.org>
[ paulmck: Remove unused "flags" variable. ]
Signed-off-by: Paul E. McKenney <paul...@kernel.org>
---
kernel/rcu/tree.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index e299cd0..3f1f574 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -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;
