linux-kernel - [PATCHi v4] rcu/kvfree: Prevents cache growing when the backoff_page_cache

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Message-Id: <20230411142733.1011223-1-qiang1.zhang@intel.com>
Date:   Tue, 11 Apr 2023 22:27:33 +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: [PATCHi v4] rcu/kvfree: Prevents cache growing when the backoff_page_cache_fill is set

Currently, in kfree_rcu_shrink_scan(), the drain_page_cache() is
executed before kfree_rcu_monitor() to drain page cache, if the bnode
structure's->gp_snap has done, the kvfree_rcu_bulk() will fill the
page cache again in kfree_rcu_monitor(), this commit add a check
for krcp structure's->backoff_page_cache_fill in put_cached_bnode(),
if the krcp structure's->backoff_page_cache_fill is set, prevent page
cache growing and start fill page from krcp->nr_bkv_objs, if the
krcp->nr_bkv_objs is greater or equal to nr_pages, not alloc page,
avoid unnecessary __get_free_page() calls.

Signed-off-by: Zqiang <qiang1.zhang@...el.com>
---
 kernel/rcu/tree.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 41daae3239b5..d5639025bd1a 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2908,6 +2908,8 @@ static inline bool
 put_cached_bnode(struct kfree_rcu_cpu *krcp,
 	struct kvfree_rcu_bulk_data *bnode)
 {
+	if (atomic_read(&krcp->backoff_page_cache_fill))
+		return false;
 	// Check the limit.
 	if (krcp->nr_bkv_objs >= rcu_min_cached_objs)
 		return false;
@@ -3223,7 +3225,7 @@ 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 = 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