[PATCH] mm/memcontrol: Export memcg->watermark via sysfs for v2 memcg

[Ganesan Rajagopal <rganesan@arista.com>]

v1 memcg exports memcg->watermark as "memory.mem_usage_in_bytes" in
sysfs. This is missing for v2 memcg though "memory.current" is exported.
There is no other easy way of getting this information in Linux.
getrsuage() returns ru_maxrss but that's the max RSS of a single process
instead of the aggregated max RSS of all the processes. Hence, expose
memcg->watermark as "memory.watermark" for v2 memcg.

Signed-off-by: Ganesan Rajagopal <rganesan@arista.com>
---
 mm/memcontrol.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 725f76723220..57ed07deff3e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6098,6 +6098,14 @@ static u64 memory_current_read(struct cgroup_subsys_state *css,
 	return (u64)page_counter_read(&memcg->memory) * PAGE_SIZE;
 }
 
+static u64 memory_watermark_read(struct cgroup_subsys_state *css,
+				 struct cftype *cft)
+{
+	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
+
+	return (u64)memcg->memory.watermark * PAGE_SIZE;
+}
+
 static int memory_min_show(struct seq_file *m, void *v)
 {
 	return seq_puts_memcg_tunable(m,
@@ -6361,6 +6369,11 @@ static struct cftype memory_files[] = {
 		.flags = CFTYPE_NOT_ON_ROOT,
 		.read_u64 = memory_current_read,
 	},
+	{
+		.name = "watermark",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.read_u64 = memory_watermark_read,
+	},
 	{
 		.name = "min",
 		.flags = CFTYPE_NOT_ON_ROOT,
-- 
2.28.0