[RFC PATCH 10/15] mm: thp: make deferred split queue lock safe when the LRU pages reparented

From: Muchun Song
Date: Tue Mar 30 2021 - 06:23:38 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 | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 186dc11e8992..434cc7283a64 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -496,6 +496,8 @@ 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;
@@ -503,6 +505,17 @@ 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;
}

@@ -512,6 +525,8 @@ 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;
@@ -519,6 +534,17 @@ 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;
+ }
+
+ /*
+ * Preemption is disabled in the internal of spin_lock, which can serve
+ * as RCU read-side critical sections.
+ */
+ rcu_read_unlock();
+
return queue;
}
#else
--
2.11.0