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From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     rcu@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, kernel-team@meta.com,
        rostedt@goodmis.org, "Uladzislau Rezki (Sony)" <urezki@gmail.com>,
        "Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH rcu 6/8] rcu/kvfree: Do not run a page work if a cache is disabled
Date:   Wed, 10 May 2023 10:02:40 -0700
Message-Id: <20230510170242.2187714-6-paulmck@kernel.org>
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From: "Uladzislau Rezki (Sony)" <urezki@gmail.com>

By default the cache size is 5 pages per CPU, but it can be disabled at
boot time by setting the rcu_min_cached_objs to zero.  When that happens,
the current code will uselessly set an hrtimer to schedule refilling this
cache with zero pages.  This commit therefore streamlines this process
by simply refusing the set the hrtimer when rcu_min_cached_objs is zero.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 51d84eabf645..18f592bf6dc6 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3225,6 +3225,10 @@ static void fill_page_cache_func(struct work_struct *work)
 static void
 run_page_cache_worker(struct kfree_rcu_cpu *krcp)
 {
+	// If cache disabled, bail out.
+	if (!rcu_min_cached_objs)
+		return;
+
 	if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING &&
 			!atomic_xchg(&krcp->work_in_progress, 1)) {
 		if (atomic_read(&krcp->backoff_page_cache_fill)) {
-- 
2.40.1