[RFC PATCH v4 06/12] mm: thp: make deferred split queue lock safe when the LRU pages reparented

From: Muchun Song
Date: Thu May 27 2021 - 05:34:46 EST


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@xxxxxxxxxxxxx>
---
mm/huge_memory.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index d8590408abbb..8f0761563d46 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -506,6 +506,8 @@ 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;
@@ -513,6 +515,17 @@ 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;
}

@@ -522,6 +535,8 @@ 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;
@@ -529,6 +544,14 @@ 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