[PATCH v2] rcu/kvfree: Make drain_page_cache() call return directly if cache is disabled

[Zqiang]

If the rcu_min_cached_objs is set to zero at boot params, the
krcp->page_cache_work will not be triggered to fill page cache,
and the put_cached_bnode() also does not fill page cache, this
also means the krcp->bkvcache is always empty, so not need to
acquire unnecessary krcp->lock to get page from krcp->bkvcache,
this commit therefore make drain_page_cache() return directly if
the rcu_min_cached_objs is zero.

Signed-off-by: Zqiang <qiang1.zhang@xxxxxxxxx>
---
 kernel/rcu/tree.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 93faf9f5c58f..00620a2117de 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2924,6 +2924,9 @@ 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);
-- 
2.32.0