[PATCH] mm: account lazily freed anon pages in NR_FILE_PAGES

[Yafang Shao <laoar.shao@gmail.com>]

The memory utilization (Used / Total) is used to monitor the memory
pressure by us. If it is too high, it means the system may be OOM sooner
or later when swap is off, then we will make adjustment on this system.

However, this method is broken since MADV_FREE is introduced, because
these lazily free anonymous can be reclaimed under memory pressure while
they are still accounted in NR_ANON_MAPPED.

Furthermore, since commit f7ad2a6cb9f7 ("mm: move MADV_FREE pages into
LRU_INACTIVE_FILE list"), these lazily free anonymous pages are moved
from anon lru list into file lru list. That means
(Inactive(file) + Active(file)) may be much larger than Cached in
/proc/meminfo. That makes our users confused.

So we'd better account the lazily freed anonoymous pages in
NR_FILE_PAGES as well.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
---
 mm/memcontrol.c | 11 +++++++++--
 mm/rmap.c       | 26 ++++++++++++++++++--------
 mm/swap.c       |  2 ++
 mm/vmscan.c     |  2 ++
 4 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3dcbf24d2227..217a6f10fa8d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5659,8 +5659,15 @@ static int mem_cgroup_move_account(struct page *page,
 
 	if (PageAnon(page)) {
 		if (page_mapped(page)) {
-			__mod_lruvec_state(from_vec, NR_ANON_MAPPED, -nr_pages);
-			__mod_lruvec_state(to_vec, NR_ANON_MAPPED, nr_pages);
+			if (!PageSwapBacked(page) && !PageSwapCache(page) &&
+			    !PageUnevictable(page)) {
+				__mod_lruvec_state(from_vec, NR_FILE_PAGES, -nr_pages);
+				__mod_lruvec_state(to_vec, NR_FILE_PAGES, nr_pages);
+			} else {
+				__mod_lruvec_state(from_vec, NR_ANON_MAPPED, -nr_pages);
+				__mod_lruvec_state(to_vec, NR_ANON_MAPPED, nr_pages);
+			}
+
 			if (PageTransHuge(page)) {
 				__mod_lruvec_state(from_vec, NR_ANON_THPS,
 						   -nr_pages);
diff --git a/mm/rmap.c b/mm/rmap.c
index 1b84945d655c..690ca7ff2392 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1312,8 +1312,13 @@ static void page_remove_anon_compound_rmap(struct page *page)
 	if (unlikely(PageMlocked(page)))
 		clear_page_mlock(page);
 
-	if (nr)
-		__mod_lruvec_page_state(page, NR_ANON_MAPPED, -nr);
+	if (nr) {
+		if (PageLRU(page) && PageAnon(page) && !PageSwapBacked(page) &&
+		    !PageSwapCache(page) && !PageUnevictable(page))
+			__mod_lruvec_page_state(page, NR_FILE_PAGES, -nr);
+		else
+			__mod_lruvec_page_state(page, NR_ANON_MAPPED, -nr);
+	}
 }
 
 /**
@@ -1341,12 +1346,17 @@ void page_remove_rmap(struct page *page, bool compound)
 	if (!atomic_add_negative(-1, &page->_mapcount))
 		goto out;
 
-	/*
-	 * We use the irq-unsafe __{inc|mod}_zone_page_stat because
-	 * these counters are not modified in interrupt context, and
-	 * pte lock(a spinlock) is held, which implies preemption disabled.
-	 */
-	__dec_lruvec_page_state(page, NR_ANON_MAPPED);
+	if (PageLRU(page) && PageAnon(page) && !PageSwapBacked(page) &&
+	    !PageSwapCache(page) && !PageUnevictable(page)) {
+		__dec_lruvec_page_state(page, NR_FILE_PAGES);
+	} else {
+		/*
+		 * We use the irq-unsafe __{inc|mod}_zone_page_stat because
+		 * these counters are not modified in interrupt context, and
+		 * pte lock(a spinlock) is held, which implies preemption disabled.
+		 */
+		__dec_lruvec_page_state(page, NR_ANON_MAPPED);
+	}
 
 	if (unlikely(PageMlocked(page)))
 		clear_page_mlock(page);
diff --git a/mm/swap.c b/mm/swap.c
index 47a47681c86b..340c5276a0f3 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -601,6 +601,7 @@ static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec,
 
 		del_page_from_lru_list(page, lruvec,
 				       LRU_INACTIVE_ANON + active);
+		__mod_lruvec_state(lruvec, NR_ANON_MAPPED, -nr_pages);
 		ClearPageActive(page);
 		ClearPageReferenced(page);
 		/*
@@ -610,6 +611,7 @@ static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec,
 		 */
 		ClearPageSwapBacked(page);
 		add_page_to_lru_list(page, lruvec, LRU_INACTIVE_FILE);
+		__mod_lruvec_state(lruvec, NR_FILE_PAGES, nr_pages);
 
 		__count_vm_events(PGLAZYFREE, nr_pages);
 		__count_memcg_events(lruvec_memcg(lruvec), PGLAZYFREE,
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1b8f0e059767..4821124c70f7 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1428,6 +1428,8 @@ static unsigned int shrink_page_list(struct list_head *page_list,
 				goto keep_locked;
 			}
 
+			mod_lruvec_page_state(page, NR_ANON_MAPPED, nr_pages);
+			mod_lruvec_page_state(page, NR_FILE_PAGES, -nr_pages);
 			count_vm_event(PGLAZYFREED);
 			count_memcg_page_event(page, PGLAZYFREED);
 		} else if (!mapping || !__remove_mapping(mapping, page, true,
-- 
2.18.4