linux-kernel - [PATCH] rcu/kvfree: Make fill page cache start from krcp->nr_bkv

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Date:   Wed, 12 Apr 2023 22:31:27 +0800
From:   Zqiang <qiang1.zhang@...el.com>
To:     urezki@...il.com, paulmck@...nel.org, frederic@...nel.org,
        joel@...lfernandes.org, qiang1.zhang@...el.com
Cc:     qiang.zhang1211@...il.com, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] rcu/kvfree: Make fill page cache start from krcp->nr_bkv_objs

The fill_page_cache_func() is invoked and start from zero to
allocate nr_pages of page, if the kfree_rcu_work() executes before
the fill_page_cache_func(), the krcp->nr_bkv_objs is updated before
enter for-loop and equal to nr_pages, since the page is allocated
first, and then check the krcp->nr_bkv_objs in put_cached_bnode(),
this produces a meaningless __get_free_page() call, this commit
therefore make allocate page start from krcp->nr_bkv_objs and
check krcp->nr_bkv_objs before allocate page.

Signed-off-by: Zqiang <qiang1.zhang@...el.com>
---
 kernel/rcu/tree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 41daae3239b5..dcb86f9f2dd6 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3223,7 +3223,7 @@ static void fill_page_cache_func(struct work_struct *work)
 	nr_pages = atomic_read(&krcp->backoff_page_cache_fill) ?
 		1 : rcu_min_cached_objs;

-	for (i = 0; i < nr_pages; i++) {
+	for (i = READ_ONCE(krcp->nr_bkv_objs); i < nr_pages; i++) {
 		bnode = (struct kvfree_rcu_bulk_data *)
 			__get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);

-- 
2.32.0