mm: memcontrol: simplify lruvec_holds_page_lru_lock

We already have a helper lruvec_memcg() to get the memcg from lruvec, we
do not need to do it ourselves in the lruvec_holds_page_lru_lock().  So
use lruvec_memcg() instead.  And if mem_cgroup_disabled() returns false,
the page_memcg(page) (the LRU pages) cannot be NULL.  So remove the odd
logic of "memcg = page_memcg(page) ?  : root_mem_cgroup".  And use
lruvec_pgdat to simplify the code.  We can have a single definition for
this function that works for !CONFIG_MEMCG, CONFIG_MEMCG +
mem_cgroup_disabled() and CONFIG_MEMCG.

Link: https://lkml.kernel.org/r/20210417043538.9793-5-songmuchun@bytedance.comSigned-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/memcontrol.h

@@ -755,22 +755,6 @@ static inline struct lruvec *mem_cgroup_page_lruvec(struct page *page)
 	return mem_cgroup_lruvec(memcg, pgdat);
 }
 
-static inline bool lruvec_holds_page_lru_lock(struct page *page,
-					      struct lruvec *lruvec)
-{
-	pg_data_t *pgdat = page_pgdat(page);
-	const struct mem_cgroup *memcg;
-	struct mem_cgroup_per_node *mz;
-
-	if (mem_cgroup_disabled())
-		return lruvec == &pgdat->__lruvec;
-
-	mz = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
-	memcg = page_memcg(page) ? : root_mem_cgroup;
-
-	return lruvec->pgdat == pgdat && mz->memcg == memcg;
-}
-
 struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
 
 struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm);
@@ -1227,14 +1211,6 @@ static inline struct lruvec *mem_cgroup_page_lruvec(struct page *page)
 	return &pgdat->__lruvec;
 }
 
-static inline bool lruvec_holds_page_lru_lock(struct page *page,
-					      struct lruvec *lruvec)
-{
-	pg_data_t *pgdat = page_pgdat(page);
-
-	return lruvec == &pgdat->__lruvec;
-}
-
 static inline void lruvec_memcg_debug(struct lruvec *lruvec, struct page *page)
 {
 }
@@ -1516,6 +1492,13 @@ static inline void unlock_page_lruvec_irqrestore(struct lruvec *lruvec,
 	spin_unlock_irqrestore(&lruvec->lru_lock, flags);
 }
 
+static inline bool lruvec_holds_page_lru_lock(struct page *page,
+					      struct lruvec *lruvec)
+{
+	return lruvec_pgdat(lruvec) == page_pgdat(page) &&
+	       lruvec_memcg(lruvec) == page_memcg(page);
+}
+
 /* Don't lock again iff page's lruvec locked */
 static inline struct lruvec *relock_page_lruvec_irq(struct page *page,
 		struct lruvec *locked_lruvec)