linux-kernel - [RFC PATCH v3 06/12] mm: thp: make deferred split queue lock safe when the LRU pages reparented

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Date:   Wed, 21 Apr 2021 15:00:53 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     guro@...com, hannes@...xchg.org, mhocko@...nel.org,
        akpm@...ux-foundation.org, shakeelb@...gle.com,
        vdavydov.dev@...il.com
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        duanxiongchun@...edance.com, fam.zheng@...edance.com,
        bsingharora@...il.com, shy828301@...il.com,
        alex.shi@...ux.alibaba.com, Muchun Song <songmuchun@...edance.com>
Subject: [RFC PATCH v3 06/12] mm: thp: make deferred split queue lock safe when the LRU pages reparented

Similar to lruvec lock, we use the same approach to make the lock safe
when the LRU pages reparented.

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 mm/huge_memory.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 05ef9e8f9af5..25025bf988f8 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -497,6 +497,8 @@ static struct deferred_split *lock_split_queue(struct page *page)
 	struct deferred_split *queue;
 	struct mem_cgroup *memcg;
 
+	rcu_read_lock();
+retry:
 	memcg = page_memcg(compound_head(page));
 	if (memcg)
 		queue = &memcg->deferred_split_queue;
@@ -504,6 +506,17 @@ static struct deferred_split *lock_split_queue(struct page *page)
 		queue = &NODE_DATA(page_to_nid(page))->deferred_split_queue;
 	spin_lock(&queue->split_queue_lock);
 
+	if (unlikely(memcg != page_memcg(page))) {
+		spin_unlock(&queue->split_queue_lock);
+		goto retry;
+	}
+
+	/*
+	 * Preemption is disabled in the internal of spin_lock, which can serve
+	 * as RCU read-side critical sections.
+	 */
+	rcu_read_unlock();
+
 	return queue;
 }
 
@@ -513,6 +526,8 @@ static struct deferred_split *lock_split_queue_irqsave(struct page *page,
 	struct deferred_split *queue;
 	struct mem_cgroup *memcg;
 
+	rcu_read_lock();
+retry:
 	memcg = page_memcg(compound_head(page));
 	if (memcg)
 		queue = &memcg->deferred_split_queue;
@@ -520,6 +535,14 @@ static struct deferred_split *lock_split_queue_irqsave(struct page *page,
 		queue = &NODE_DATA(page_to_nid(page))->deferred_split_queue;
 	spin_lock_irqsave(&queue->split_queue_lock, *flags);
 
+	if (unlikely(memcg != page_memcg(page))) {
+		spin_unlock_irqrestore(&queue->split_queue_lock, *flags);
+		goto retry;
+	}
+
+	/* See the comments in lock_split_queue(). */
+	rcu_read_unlock();
+
 	return queue;
 }
 #else
-- 
2.11.0