[PATCH RFC] mm: memcontrol: add cgroup v2 interface to read memory watermark

[Xi Ruoyao]

Introduce a control file memory.watermark showing the watermark
consumption of the cgroup and its descendants, in bytes.

Signed-off-by: Xi Ruoyao <xry111@xxxxxxxxxxxxxxxx>
---
 mm/memcontrol.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ba9138a4a1de..b1d968f2adcd 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5495,6 +5495,13 @@ 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,
@@ -5771,6 +5778,11 @@ 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,
-- 
Xi Ruoyao <xry111@xxxxxxxxxxxxxxxx>
School of Aerospace Science and Technology, Xidian University