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

[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@mengyan1223.wang>
---
 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@mengyan1223.wang>
School of Aerospace Science and Technology, Xidian University

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

[Tejun Heo]

On Sat, Jun 15, 2019 at 04:20:04PM +0800, Xi Ruoyao wrote:
> Introduce a control file memory.watermark showing the watermark
> consumption of the cgroup and its descendants, in bytes.
> 
> Signed-off-by: Xi Ruoyao <xry111@mengyan1223.wang>

Memory usage w/o pressure metric isn't all that useful and reporting
just the historical maximum of memory.current can be outright
misleading.  The use case of determining maximum amount of required
memory is legit but it needs to maintain sustained positive pressure
while taking measurements.  There are efforts on this front, so let's
not merge this one for now.

Nacked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun