[PATCH v2] mm, memcg: add workingset_restore in memory.stat

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

There's a new workingset counter introduced in commit 1899ad18c607 ("mm:
workingset: tell cache transitions from workingset thrashing"). With the
help of this counter we can know the workingset is transitioning or
thrashing. To leverage the benifit of this counter to memcg, we should
introduce it into memory.stat. Then we could know the workingset of the
workload inside a memcg better.

Bellow is the verification of this new counter in memory.stat.
Read a file into the memory and then read it again to make these pages be
active. The size of this file is 1G. (memory.max is greater than file size)
The counters in memory.stat will be,
	inactive_file 0
	active_file 1073639424

	workingset_refault 0
	workingset_activate 0
	workingset_restore 0
	workingset_nodereclaim 0
Trigger the memcg reclaim by setting a lower value to memory.high, and
then some pages will be demoted into inactive list, and then some pages
in the inactive list will be evicted into the storage.
	inactive_file 498094080
	active_file 310063104

	workingset_refault 0
	workingset_activate 0
	workingset_restore 0
	workingset_nodereclaim 0
Then recover the memory.high and read the file into memory again. As a
result of it, the transitioning will occur. Bellow is the result of this
transitioning,
	inactive_file 498094080
	active_file 575397888

	workingset_refault 64746
	workingset_activate 64746
	workingset_restore 64746
	workingset_nodereclaim 0

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
---
 Documentation/admin-guide/cgroup-v2.rst | 3 +++
 mm/memcontrol.c                         | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index bcc80269bb6a..0733b659e757 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1329,6 +1329,9 @@ PAGE_SIZE multiple when read back.
 	  workingset_activate
 		Number of refaulted pages that were immediately activated
 
+	  workingset_restore
+		Number of transitioning of refaulted pages
+
 	  workingset_nodereclaim
 		Number of times a shadow node has been reclaimed
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 5beea03dd58a..0395e479995b 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1451,6 +1451,8 @@ static char *memory_stat_format(struct mem_cgroup *memcg)
 		       memcg_page_state(memcg, WORKINGSET_REFAULT));
 	seq_buf_printf(&s, "workingset_activate %lu\n",
 		       memcg_page_state(memcg, WORKINGSET_ACTIVATE));
+	seq_buf_printf(&s, "workingset_restore %lu\n",
+		       memcg_page_state(memcg, WORKINGSET_RESTORE));
 	seq_buf_printf(&s, "workingset_nodereclaim %lu\n",
 		       memcg_page_state(memcg, WORKINGSET_NODERECLAIM));
 
-- 
2.18.2