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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, Zqiang <qiang1.zhang@intel.com>,
        Uladzislau Rezki <urezki@gmail.com>,
        "Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH rcu 8/8] rcu/kvfree: Make drain_page_cache() take early return if cache is disabled
Date:   Wed, 10 May 2023 10:02:42 -0700
Message-Id: <20230510170242.2187714-8-paulmck@kernel.org>
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From: Zqiang <qiang1.zhang@intel.com>

If the rcutree.rcu_min_cached_objs kernel boot parameter is set to zero,
then krcp->page_cache_work will never be triggered to fill page cache.
In addition, the put_cached_bnode() will not fill page cache.  As a
result krcp->bkvcache will always be empty, so there is no need to acquire
krcp->lock to get page from krcp->bkvcache.  This commit therefore makes
drain_page_cache() return immediately if the rcu_min_cached_objs is zero.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 98f2e833e217..00ed45ddc6ca 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2902,6 +2902,9 @@ drain_page_cache(struct kfree_rcu_cpu *krcp)
 	struct llist_node *page_list, *pos, *n;
 	int freed = 0;
 
+	if (!rcu_min_cached_objs)
+		return 0;
+
 	raw_spin_lock_irqsave(&krcp->lock, flags);
 	page_list = llist_del_all(&krcp->bkvcache);
 	WRITE_ONCE(krcp->nr_bkv_objs, 0);
-- 
2.40.1