[PATCH v2] cgroup/dmem: introduce a peak file

[Thadeu Lima de Souza Cascardo <cascardo@igalia.com>]

Just like we have memory.peak, introduce a dmem.peak, which uses the
page_counter support for that.

For now, make it read-only.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
---
Changes in v2:
- Make it read-only for now and adjust documentation accordingly.
- Link to v1: https://patch.msgid.link/20260506-dmem_peak-v1-0-8d803eb3449c@igalia.com
---
 Documentation/admin-guide/cgroup-v2.rst |  6 ++++++
 kernel/cgroup/dmem.c                    | 15 +++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 6efd0095ed99..d103623b2be4 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -2808,6 +2808,12 @@ DMEM Interface Files
 	The semantics are the same as for the memory cgroup controller, and are
 	calculated in the same way.
 
+  dmem.peak
+	A read-only nested-keyed file that exists on non-root cgroups.
+
+	The max device memory usage recorded for the cgroup and its
+	descendants since the creation of the cgroup for each region.
+
   dmem.capacity
 	A read-only file that describes maximum region capacity.
 	It only exists on the root cgroup. Not all memory can be
diff --git a/kernel/cgroup/dmem.c b/kernel/cgroup/dmem.c
index 4753a67d0f0f..6430c7ce1e03 100644
--- a/kernel/cgroup/dmem.c
+++ b/kernel/cgroup/dmem.c
@@ -182,6 +182,11 @@ static u64 get_resource_current(struct dmem_cgroup_pool_state *pool)
 	return pool ? page_counter_read(&pool->cnt) : 0;
 }
 
+static u64 get_resource_peak(struct dmem_cgroup_pool_state *pool)
+{
+	return pool ? READ_ONCE(pool->cnt.watermark) : 0;
+}
+
 static void reset_all_resource_limits(struct dmem_cgroup_pool_state *rpool)
 {
 	set_resource_min(rpool, 0);
@@ -808,6 +813,11 @@ static int dmemcg_limit_show(struct seq_file *sf, void *v,
 	return 0;
 }
 
+static int dmem_cgroup_region_peak_show(struct seq_file *sf, void *v)
+{
+	return dmemcg_limit_show(sf, v, get_resource_peak);
+}
+
 static int dmem_cgroup_region_current_show(struct seq_file *sf, void *v)
 {
 	return dmemcg_limit_show(sf, v, get_resource_current);
@@ -856,6 +866,11 @@ static struct cftype files[] = {
 		.name = "current",
 		.seq_show = dmem_cgroup_region_current_show,
 	},
+	{
+		.name = "peak",
+		.seq_show = dmem_cgroup_region_peak_show,
+		.flags = CFTYPE_NOT_ON_ROOT,
+	},
 	{
 		.name = "min",
 		.write = dmem_cgroup_region_min_write,

---
base-commit: d3b0a7f21119f5a66cb76aa28fb8cc13206aaf7d
change-id: 20260409-dmem_peak-3abc1be95072

Best regards,
--  
Thadeu Lima de Souza Cascardo <cascardo@igalia.com>