[PATCH v9 19/20] mm/lru: add debug checking for page memcg moving

[Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>]

This debug patch could give some clues if there are sth out of
consideration.

Hugh Dickins reported a bug of this patch, Thanks!

Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: cgroups@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 include/linux/memcontrol.h |  6 ++++++
 mm/compaction.c            |  2 ++
 mm/memcontrol.c            | 15 +++++++++++++++
 3 files changed, 23 insertions(+)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index f60009580d2a..27c7bbe82125 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -431,6 +431,8 @@ struct lruvec *lock_page_lruvec_irqsave(struct page *page,
 void unlock_page_lruvec_irq(struct lruvec *lruvec);
 void unlock_page_lruvec_irqrestore(struct lruvec *lruvec, unsigned long flags);
 
+void lruvec_memcg_debug(struct lruvec *lruvec, struct page *page);
+
 static inline
 struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *css){
 	return css ? container_of(css, struct mem_cgroup, css) : NULL;
@@ -1191,6 +1193,10 @@ static inline void count_memcg_page_event(struct page *page,
 void count_memcg_event_mm(struct mm_struct *mm, enum vm_event_item idx)
 {
 }
+
+static inline void lruvec_memcg_debug(struct lruvec *lruvec, struct page *page)
+{
+}
 #endif /* CONFIG_MEMCG */
 
 /* idx can be of type enum memcg_stat_item or node_stat_item */
diff --git a/mm/compaction.c b/mm/compaction.c
index 4a773f0ffedf..40c270bd5092 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -984,6 +984,8 @@ static bool too_many_isolated(pg_data_t *pgdat)
 			compact_lock_irqsave(&lruvec->lru_lock, &flags, cc);
 			locked_lruvec = lruvec;
 
+			lruvec_memcg_debug(lruvec, page);
+
 			/* Try get exclusive access under lock */
 			if (!skip_updated) {
 				skip_updated = true;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 099926efbb48..2d71e53ead88 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1240,6 +1240,19 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgd
 	return lruvec;
 }
 
+void lruvec_memcg_debug(struct lruvec *lruvec, struct page *page)
+{
+#ifdef CONFIG_DEBUG_VM
+	if (mem_cgroup_disabled())
+		return;
+
+	if (!page->mem_cgroup)
+		VM_BUG_ON_PAGE(lruvec_memcg(lruvec) != root_mem_cgroup, page);
+	else
+		VM_BUG_ON_PAGE(lruvec_memcg(lruvec) != page->mem_cgroup, page);
+#endif
+}
+
 /* page must be isolated */
 struct lruvec *lock_page_lruvec_irq(struct page *page)
 {
@@ -1248,6 +1261,7 @@ struct lruvec *lock_page_lruvec_irq(struct page *page)
 	lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
 	spin_lock_irq(&lruvec->lru_lock);
 
+	lruvec_memcg_debug(lruvec, page);
 	return lruvec;
 }
 
@@ -1258,6 +1272,7 @@ struct lruvec *lock_page_lruvec_irqsave(struct page *page, unsigned long *flags)
 	lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
 	spin_lock_irqsave(&lruvec->lru_lock, *flags);
 
+	lruvec_memcg_debug(lruvec, page);
 	return lruvec;
 }
 
-- 
1.8.3.1