[PATCH rcu 8/8] rcu/kvfree: Make drain_page_cache() take early return if cache is disabled

From: Paul E. McKenney
Date: Wed May 10 2023 - 13:03:38 EST

From: Zqiang <qiang1.zhang@xxxxxxxxx>

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@xxxxxxxxx>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
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);