[PATCH v6 0/3] cgroup: dmem: add selftest helper and coverage

[PATCH v6 0/3] cgroup: dmem: add selftest helper and coverage

[Albert Esteve]

Hi all,

This small series adds practical test coverage for the dmem
cgroup controller.

The motivation came from following the recent dmem API discussion in
thread [1]. That discussion considered changing the dmem API and
adding a new knob. Currently there are no dedicated tests covering
dmem behaviour, which makes such changes riskier.

Adding selftests has an additional challenge: dmem charging paths
are driver-driven today, so regression testing is harder unless a
suitable driver is present in the test environment.

This series addresses that by adding:
- an out-of-tree dmem_selftest helper with alloc/free module parameters,
- KB() definition next to existing MB()/GB() helpers
- test_dmem for dmem.max enforcement and byte-accurate dmem.current

The goal is to make dmem behavior easier to validate when evolving the API
and implementation, while keeping tests deterministic and driver-independent.

Thanks.

[1] - https://lore.kernel.org/all/aZoHfloupKvF2oSu@fedora/

Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
Changes in v6:
- Drop virtme-ng wrappers
- Build the helper out of tree, drop CONFIG_DMEM_SELFTEST
- Rename charge/uncharge to alloc/free
- Add KB() in cgroup_util.h
- Use cg_read_key_long(), ARRAY_SIZE(), and KB()/MB() size literals
- Drop test_dmem_min/low
- Check dmem.current for exact equality
- stat() the helper once in main() instead of per-subtest
- Link to v5: https://lore.kernel.org/r/20260706-kunit_cgroups-v5-0-6c42c8753468@redhat.com

Changes in v5:
- Change parse_first_region() by find_selftest_region to scan
  dmem.capacity lines
- Use exact equality for limit readback, not values_close()
- Write VM tempfile to $SCRIPT_DIR
- Fix KTAP by dropping outer framing in test_dmem
- Use array for optional vng args to handle paths with spaces
- Respect O=/KBUILD_OUTPUT= when building, per bpf/vmtest.sh convention
- Link to v4: https://lore.kernel.org/r/20260519-kunit_cgroups-v4-0-f6c2f498fae4@redhat.com

Changes in v4:
- Fix charged_pool leak in dmem_selftest_init()
- Replace ssh-based VM approach in vmtest-dmem.sh with vng --exec
- Add main() wrapper to vmtest-dmem.sh
- Other small fixes suggested by Sashiko
- Link to v3: https://lore.kernel.org/r/20260504-kunit_cgroups-v3-0-4eac90b76f91@redhat.com

Changes in v3:
- Set charged flag on unexpected over-limit charge success.
- Add CONFIG_DMEM_SELFTEST=m to selftest config.
- Simplify -v to a boolean; single -v was a no-op.
- Unquote kernel_opt to avoid empty-string arg to vng.
- Document -b in usage() output.
- Link to v2: https://lore.kernel.org/r/20260421-kunit_cgroups-v2-0-bb6675d8249c@redhat.com

Changes in v2:
- Fix debugfs_create_dir() error check
- Fix module teardown race: call dmem_selftest_remove() before
  uncharging so debugfs files are torn down
- Use IS_ERR_OR_NULL() in selftest() sanity check
- Add CONFIG_CGROUP_DMEM=y to the cgroup selftest config
- Replace config-file parsing in check_guest_requirements() with
  a direct check of /sys/fs/cgroup/cgroup.controllers
- Add new patch 4 (from Eric Chanudet): vmtest-dmem.sh -b flag
  to configure and build a local kernel tree
- Link to v1: https://lore.kernel.org/r/20260327-kunit_cgroups-v1-0-971b3c739a00@redhat.com

---
Albert Esteve (3):
      selftests: cgroup: Add dmem_selftest helper module
      selftests: cgroup: Add KB() helper
      selftests: cgroup: Add dmem selftest coverage

 tools/testing/selftests/cgroup/.gitignore          |   1 +
 tools/testing/selftests/cgroup/Makefile            |   3 +
 tools/testing/selftests/cgroup/config              |   1 +
 .../selftests/cgroup/lib/include/cgroup_util.h     |   1 +
 tools/testing/selftests/cgroup/test_dmem.c         | 314 +++++++++++++++++++++
 .../testing/selftests/cgroup/test_modules/Makefile |  17 ++
 .../selftests/cgroup/test_modules/dmem_selftest.c  | 146 ++++++++++
 7 files changed, 483 insertions(+)
---
base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
change-id: 20260318-kunit_cgroups-7fb0b9e64017

Best regards,
-- 
Albert Esteve <aesteve@redhat.com>

[PATCH v6 1/3] selftests: cgroup: Add dmem_selftest helper module

[Albert Esteve]

Currently, dmem charging is driver-driven through direct
calls to dmem_cgroup_try_charge() (for example TTM).
That does not give cgroup selftests a generic way to
trigger alloc/free paths from userspace in a chosen
cgroup, so coverage of nested dmem.max still
needs a synthetic region.

Add tools/testing/selftests/cgroup/test_modules/dmem_selftest.c
as an OOT helper, built like other test_modules (no extra
Kconfig needed). Tests can insmod the .ko module to register a
"dmem_selftest" region.

Module parameters drive a single outstanding allocation against
the calling task's cgroup:

  /sys/module/dmem_selftest/parameters/alloc
  /sys/module/dmem_selftest/parameters/free

Writing a size to alloc triggers dmem_cgroup_try_charge() for
the calling task's cgroup. Writing to free with no argument
releases the outstanding charge via dmem_cgroup_uncharge().
Only a single outstanding charge is supported.

This provides a deterministic, driver-independent mechanism
for exercising dmem accounting paths in selftests.

Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
 tools/testing/selftests/cgroup/Makefile            |   1 +
 tools/testing/selftests/cgroup/config              |   1 +
 .../testing/selftests/cgroup/test_modules/Makefile |  17 +++
 .../selftests/cgroup/test_modules/dmem_selftest.c  | 146 +++++++++++++++++++++
 4 files changed, 165 insertions(+)

diff --git a/tools/testing/selftests/cgroup/Makefile b/tools/testing/selftests/cgroup/Makefile
index e01584c2189a..a08661320a07 100644
--- a/tools/testing/selftests/cgroup/Makefile
+++ b/tools/testing/selftests/cgroup/Makefile
@@ -6,6 +6,7 @@ all: ${HELPER_PROGS}
 TEST_FILES     := with_stress.sh
 TEST_PROGS     := test_stress.sh test_cpuset_prs.sh test_cpuset_v1_hp.sh
 TEST_GEN_FILES := wait_inotify
+TEST_GEN_MODS_DIR := test_modules
 # Keep the lists lexicographically sorted
 TEST_GEN_PROGS  = test_core
 TEST_GEN_PROGS += test_cpu
diff --git a/tools/testing/selftests/cgroup/config b/tools/testing/selftests/cgroup/config
index 39f979690dd3..2ee0488c3d65 100644
--- a/tools/testing/selftests/cgroup/config
+++ b/tools/testing/selftests/cgroup/config
@@ -1,5 +1,6 @@
 CONFIG_CGROUPS=y
 CONFIG_CGROUP_CPUACCT=y
+CONFIG_CGROUP_DMEM=y
 CONFIG_CGROUP_FREEZER=y
 CONFIG_CGROUP_SCHED=y
 CONFIG_MEMCG=y
diff --git a/tools/testing/selftests/cgroup/test_modules/Makefile b/tools/testing/selftests/cgroup/test_modules/Makefile
new file mode 100644
index 000000000000..dd8a17313cec
--- /dev/null
+++ b/tools/testing/selftests/cgroup/test_modules/Makefile
@@ -0,0 +1,17 @@
+# SPDX-License-Identifier: GPL-2.0
+TESTMODS_DIR := $(realpath $(dir $(abspath $(lastword $(MAKEFILE_LIST)))))
+KDIR ?= /lib/modules/$(shell uname -r)/build
+
+obj-m += dmem_selftest.o
+
+# Ensure that KDIR exists, otherwise skip the compilation
+modules:
+ifneq ("$(wildcard $(KDIR))", "")
+	$(Q)$(MAKE) -C $(KDIR) modules KBUILD_EXTMOD=$(TESTMODS_DIR)
+endif
+
+# Ensure that KDIR exists, otherwise skip the clean target
+clean:
+ifneq ("$(wildcard $(KDIR))", "")
+	$(Q)$(MAKE) -C $(KDIR) clean KBUILD_EXTMOD=$(TESTMODS_DIR)
+endif
diff --git a/tools/testing/selftests/cgroup/test_modules/dmem_selftest.c b/tools/testing/selftests/cgroup/test_modules/dmem_selftest.c
new file mode 100644
index 000000000000..a763a156f13f
--- /dev/null
+++ b/tools/testing/selftests/cgroup/test_modules/dmem_selftest.c
@@ -0,0 +1,146 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Kselftest helper for the dmem cgroup controller.
+ *
+ * Registers a synthetic dmem region so tests can trigger allocations
+ * from the calling task's cgroup via module parameters:
+ *   /sys/module/dmem_selftest/parameters/alloc
+ *   /sys/module/dmem_selftest/parameters/free
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/cgroup_dmem.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/mutex.h>
+#include <linux/panic.h>
+#include <linux/sysfs.h>
+
+#define DM_SELFTEST_REGION_NAME	"dmem_selftest"
+#define DM_SELFTEST_REGION_SIZE	(256ULL * 1024 * 1024)
+
+static struct dmem_cgroup_region *selftest_region;
+static struct dmem_cgroup_pool_state *alloc_pool;
+static u64 alloc_size;
+static DEFINE_MUTEX(alloc_lock);
+
+static int param_set_alloc(const char *val, const struct kernel_param *kp)
+{
+	struct dmem_cgroup_pool_state *pool = NULL, *limit = NULL;
+	u64 size;
+	int ret;
+
+	if (!selftest_region)
+		return -ENODEV;
+
+	ret = kstrtou64(val, 0, &size);
+	if (ret)
+		return ret;
+	if (!size || size > DM_SELFTEST_REGION_SIZE)
+		return -EINVAL;
+
+	mutex_lock(&alloc_lock);
+	if (alloc_pool) {
+		mutex_unlock(&alloc_lock);
+		return -EBUSY;
+	}
+
+	ret = dmem_cgroup_try_charge(selftest_region, size, &pool, &limit);
+	if (ret == -EAGAIN && limit)
+		dmem_cgroup_pool_state_put(limit);
+	if (ret) {
+		mutex_unlock(&alloc_lock);
+		return ret;
+	}
+
+	alloc_pool = pool;
+	alloc_size = size;
+	mutex_unlock(&alloc_lock);
+	return 0;
+}
+
+static int param_get_alloc(char *buffer, const struct kernel_param *kp)
+{
+	u64 size;
+
+	mutex_lock(&alloc_lock);
+	size = alloc_size;
+	mutex_unlock(&alloc_lock);
+	return sysfs_emit(buffer, "%llu\n", size);
+}
+
+static const struct kernel_param_ops alloc_ops = {
+	.set = param_set_alloc,
+	.get = param_get_alloc,
+};
+
+module_param_cb(alloc, &alloc_ops, NULL, 0644);
+MODULE_PARM_DESC(alloc, "Allocate (charge) SIZE bytes against the calling task's dmem cgroup");
+
+static int param_set_free(const char *val, const struct kernel_param *kp)
+{
+	mutex_lock(&alloc_lock);
+	if (!alloc_pool) {
+		mutex_unlock(&alloc_lock);
+		return -EINVAL;
+	}
+
+	dmem_cgroup_uncharge(alloc_pool, alloc_size);
+	alloc_pool = NULL;
+	alloc_size = 0;
+	mutex_unlock(&alloc_lock);
+	return 0;
+}
+
+static const struct kernel_param_ops free_ops = {
+	.flags = KERNEL_PARAM_OPS_FL_NOARG,
+	.set = param_set_free,
+};
+
+module_param_cb(free, &free_ops, NULL, 0200);
+MODULE_PARM_DESC(free, "Free the outstanding dmem selftest allocation");
+
+static int __init dmem_selftest_init(void)
+{
+	static const struct dmem_cgroup_init init = {
+		.size = DM_SELFTEST_REGION_SIZE,
+	};
+
+	selftest_region = dmem_cgroup_register_region(&init, DM_SELFTEST_REGION_NAME);
+	if (IS_ERR(selftest_region))
+		return PTR_ERR(selftest_region);
+	if (!selftest_region)
+		return -EINVAL;
+
+	add_taint(TAINT_TEST, LOCKDEP_STILL_OK);
+	pr_info("region '%s' registered; parameters alloc/free\n",
+		DM_SELFTEST_REGION_NAME);
+	return 0;
+}
+
+static void __exit dmem_selftest_exit(void)
+{
+	mutex_lock(&alloc_lock);
+	if (alloc_pool) {
+		dmem_cgroup_uncharge(alloc_pool, alloc_size);
+		alloc_pool = NULL;
+		alloc_size = 0;
+	}
+	mutex_unlock(&alloc_lock);
+
+	if (selftest_region) {
+		dmem_cgroup_unregister_region(selftest_region);
+		selftest_region = NULL;
+	}
+	pr_info("unloaded.\n");
+}
+
+module_init(dmem_selftest_init);
+module_exit(dmem_selftest_exit);
+
+MODULE_AUTHOR("Albert Esteve <aesteve@redhat.com>");
+MODULE_DESCRIPTION("Kselftest helper for cgroup dmem controller");
+MODULE_LICENSE("GPL");
+MODULE_INFO(test, "Y");

-- 
2.55.0

[PATCH v6 2/3] selftests: cgroup: Add KB() helper

[Albert Esteve]

cgroup_util.h already has MB() and GB() for size
literals. Add KB() in the same style so tests can
spell kilobyte values without in-code shifts.

Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
 tools/testing/selftests/cgroup/lib/include/cgroup_util.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
index 5d39c709ac7a..0e5d7b87ad19 100644
--- a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
+++ b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
@@ -6,6 +6,7 @@
 #define BUF_SIZE 4096
 #endif
 
+#define KB(x) (x << 10)
 #define MB(x) (x << 20)
 #define GB(x) ((unsigned long long)(x) << 30)
 

-- 
2.55.0

[PATCH v6 3/3] selftests: cgroup: Add dmem selftest coverage

[Albert Esteve]

Currently, tools/testing/selftests/cgroup/ has no
dmem-specific test. This leaves dmem accounting and
dmem.max enforcement largely unvalidated without a
production driver.

Add test_dmem, driven by the dmem_selftest helper module
parameters (alloc/free) on the dmem_selftest region.
insmod the helper before running the tests.

The tests cover:
- test_dmem_max: nested hierarchy with per-leaf dmem.max
  values and verifies that over-limit charges fail while
  in-limit charges succeed in dmem.current.
- test_dmem_alloc_byte_granularity: non-page-aligned alloc
  sizes, dmem.current equals the requested byte count, and
  free-to-zero behavior.

Limits are read with cg_read_key_long(). The helper is stat'd
in main() so a missing module skips the whole test instead
of each subtest.

Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
 tools/testing/selftests/cgroup/.gitignore  |   1 +
 tools/testing/selftests/cgroup/Makefile    |   2 +
 tools/testing/selftests/cgroup/test_dmem.c | 314 +++++++++++++++++++++++++++++
 3 files changed, 317 insertions(+)

diff --git a/tools/testing/selftests/cgroup/.gitignore b/tools/testing/selftests/cgroup/.gitignore
index 952e4448bf07..ea2322598217 100644
--- a/tools/testing/selftests/cgroup/.gitignore
+++ b/tools/testing/selftests/cgroup/.gitignore
@@ -2,6 +2,7 @@
 test_core
 test_cpu
 test_cpuset
+test_dmem
 test_freezer
 test_hugetlb_memcg
 test_kill
diff --git a/tools/testing/selftests/cgroup/Makefile b/tools/testing/selftests/cgroup/Makefile
index a08661320a07..d01e8eb1ead2 100644
--- a/tools/testing/selftests/cgroup/Makefile
+++ b/tools/testing/selftests/cgroup/Makefile
@@ -11,6 +11,7 @@ TEST_GEN_MODS_DIR := test_modules
 TEST_GEN_PROGS  = test_core
 TEST_GEN_PROGS += test_cpu
 TEST_GEN_PROGS += test_cpuset
+TEST_GEN_PROGS += test_dmem
 TEST_GEN_PROGS += test_freezer
 TEST_GEN_PROGS += test_hugetlb_memcg
 TEST_GEN_PROGS += test_kill
@@ -27,6 +28,7 @@ include lib/libcgroup.mk
 $(OUTPUT)/test_core: $(LIBCGROUP_O)
 $(OUTPUT)/test_cpu: $(LIBCGROUP_O)
 $(OUTPUT)/test_cpuset: $(LIBCGROUP_O)
+$(OUTPUT)/test_dmem: $(LIBCGROUP_O)
 $(OUTPUT)/test_freezer: $(LIBCGROUP_O)
 $(OUTPUT)/test_hugetlb_memcg: $(LIBCGROUP_O)
 $(OUTPUT)/test_kill: $(LIBCGROUP_O)
diff --git a/tools/testing/selftests/cgroup/test_dmem.c b/tools/testing/selftests/cgroup/test_dmem.c
new file mode 100644
index 000000000000..3793664678b9
--- /dev/null
+++ b/tools/testing/selftests/cgroup/test_dmem.c
@@ -0,0 +1,314 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test the dmem (device memory) cgroup controller.
+ *
+ * Depends on the dmem_selftest helper module
+ * (tools/testing/selftests/cgroup/test_modules/dmem_selftest.c).
+ */
+
+#define _GNU_SOURCE
+
+#include <linux/limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "kselftest.h"
+#include "cgroup_util.h"
+
+#define DM_SELFTEST_REGION	"dmem_selftest"
+#define DM_SELFTEST_ALLOC	"/sys/module/dmem_selftest/parameters/alloc"
+#define DM_SELFTEST_FREE	"/sys/module/dmem_selftest/parameters/free"
+
+static long dmem_read_limit(const char *cgroup, const char *ctrl)
+{
+	return cg_read_key_long(cgroup, ctrl, DM_SELFTEST_REGION " ");
+}
+
+static int dmem_write_limit(const char *cgroup, const char *ctrl, long val)
+{
+	char wr[64];
+
+	snprintf(wr, sizeof(wr), "%s %ld", DM_SELFTEST_REGION, val);
+	return cg_write(cgroup, ctrl, wr);
+}
+
+static int dmem_selftest_alloc(long bytes)
+{
+	char wr[32];
+
+	snprintf(wr, sizeof(wr), "%ld", bytes);
+	return write_text(DM_SELFTEST_ALLOC, wr, strlen(wr));
+}
+
+static int dmem_selftest_free(void)
+{
+	char wr[] = "1";
+
+	return write_text(DM_SELFTEST_FREE, wr, strlen(wr));
+}
+
+/*
+ * First, this test creates the following hierarchy:
+ * A
+ * A/B     dmem.max=8M
+ * A/B/C   dmem.max=2M
+ * A/B/D   dmem.max=1M
+ * A/B/E   dmem.max=75K
+ * A/B/F   dmem.max=25K
+ * A/B/G   dmem.max=8K
+ * A/B/H   dmem.max=0
+ *
+ * Then for each leaf cgroup it tries to alloc above dmem.max
+ * and expects the request to fail and dmem.current to remain
+ * unchanged.
+ *
+ * For leaves with non-zero dmem.max, it additionally allocs a
+ * smaller amount and verifies dmem.current matches the requested
+ * size exactly (the controller accounts in bytes, with no page
+ * rounding), then frees and verifies dmem.current returns
+ * to the previous value.
+ */
+static int test_dmem_max(const char *root)
+{
+	static const long leaf_max[] = {
+		MB(2), MB(1), KB(75), KB(25), KB(8), 0
+	};
+	static const long pass_sz[] = {
+		MB(1), MB(1), KB(4), KB(4), KB(4), 0
+	};
+	char *parent[2] = {NULL};
+	char *children[ARRAY_SIZE(leaf_max)] = {NULL};
+
+	_Static_assert(ARRAY_SIZE(pass_sz) == ARRAY_SIZE(leaf_max),
+		       "pass_sz doesn't match leaf_max length");
+	long cur_before, cur_after;
+	int ret = KSFT_FAIL;
+	int charged = 0;
+	int in_child = 0;
+	long v;
+	int i;
+
+	parent[0] = cg_name(root, "dmem_prot_0");
+	if (!parent[0])
+		goto cleanup;
+
+	parent[1] = cg_name(parent[0], "dmem_prot_1");
+	if (!parent[1])
+		goto cleanup;
+
+	if (cg_create(parent[0]))
+		goto cleanup;
+
+	if (cg_write(parent[0], "cgroup.subtree_control", "+dmem"))
+		goto cleanup;
+
+	if (cg_create(parent[1]))
+		goto cleanup;
+
+	if (cg_write(parent[1], "cgroup.subtree_control", "+dmem"))
+		goto cleanup;
+
+	for (i = 0; i < ARRAY_SIZE(children); i++) {
+		children[i] = cg_name_indexed(parent[1], "dmem_child", i);
+		if (!children[i])
+			goto cleanup;
+		if (cg_create(children[i]))
+			goto cleanup;
+	}
+
+	if (dmem_write_limit(parent[1], "dmem.max", MB(8)))
+		goto cleanup;
+	for (i = 0; i < ARRAY_SIZE(children); i++)
+		if (dmem_write_limit(children[i], "dmem.max", leaf_max[i]))
+			goto cleanup;
+
+	v = dmem_read_limit(parent[1], "dmem.max");
+	if (v != MB(8))
+		goto cleanup;
+	for (i = 0; i < ARRAY_SIZE(children); i++) {
+		v = dmem_read_limit(children[i], "dmem.max");
+		if (v != leaf_max[i])
+			goto cleanup;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(children); i++) {
+		if (cg_enter_current(children[i]))
+			goto cleanup;
+		in_child = 1;
+
+		cur_before = dmem_read_limit(children[i], "dmem.current");
+		if (cur_before < 0)
+			goto cleanup;
+
+		if (dmem_selftest_alloc(leaf_max[i] + 1) >= 0) {
+			charged = 1;
+			goto cleanup;
+		}
+
+		cur_after = dmem_read_limit(children[i], "dmem.current");
+		if (cur_after != cur_before)
+			goto cleanup;
+
+		if (pass_sz[i] > 0) {
+			if (dmem_selftest_alloc(pass_sz[i]) < 0)
+				goto cleanup;
+			charged = 1;
+
+			cur_after = dmem_read_limit(children[i], "dmem.current");
+			if (cur_after != cur_before + pass_sz[i])
+				goto cleanup;
+
+			if (dmem_selftest_free() < 0)
+				goto cleanup;
+			charged = 0;
+
+			cur_after = dmem_read_limit(children[i], "dmem.current");
+			if (cur_after != cur_before)
+				goto cleanup;
+		}
+
+		if (cg_enter_current(root))
+			goto cleanup;
+		in_child = 0;
+	}
+
+	ret = KSFT_PASS;
+
+cleanup:
+	if (charged)
+		dmem_selftest_free();
+	if (in_child)
+		cg_enter_current(root);
+	for (i = ARRAY_SIZE(children) - 1; i >= 0; i--) {
+		if (!children[i])
+			continue;
+		cg_destroy(children[i]);
+		free(children[i]);
+	}
+	for (i = ARRAY_SIZE(parent) - 1; i >= 0; i--) {
+		if (!parent[i])
+			continue;
+		cg_destroy(parent[i]);
+		free(parent[i]);
+	}
+	return ret;
+}
+
+/*
+ * Alloc non-page-aligned byte sizes and verify dmem.current matches
+ * the requested size exactly. The controller charges the byte count
+ * passed to dmem_cgroup_try_charge() with no page rounding, for this
+ * helper and for production drivers. Then free must return usage to 0.
+ */
+static int test_dmem_alloc_byte_granularity(const char *root)
+{
+	static const long sizes[] = {
+		1, 4095, 4097, KB(75) + 1, MB(1), MB(1) + 1
+	};
+	char *cg = NULL;
+	long cur;
+	int ret = KSFT_FAIL;
+	int charged = 0;
+	int in_child = 0;
+	size_t i;
+
+	cg = cg_name(root, "dmem_dbg_byte_gran");
+	if (!cg)
+		goto cleanup;
+
+	if (cg_create(cg))
+		goto cleanup;
+
+	if (dmem_write_limit(cg, "dmem.max", MB(16)))
+		goto cleanup;
+
+	if (cg_enter_current(cg))
+		goto cleanup;
+	in_child = 1;
+
+	for (i = 0; i < ARRAY_SIZE(sizes); i++) {
+		if (dmem_selftest_alloc(sizes[i]) < 0)
+			goto cleanup;
+		charged = 1;
+
+		cur = dmem_read_limit(cg, "dmem.current");
+		if (cur != sizes[i])
+			goto cleanup;
+
+		if (dmem_selftest_free() < 0)
+			goto cleanup;
+		charged = 0;
+
+		cur = dmem_read_limit(cg, "dmem.current");
+		if (cur != 0)
+			goto cleanup;
+	}
+
+	ret = KSFT_PASS;
+
+cleanup:
+	if (charged)
+		dmem_selftest_free();
+	if (in_child)
+		cg_enter_current(root);
+	if (cg) {
+		cg_destroy(cg);
+		free(cg);
+	}
+	return ret;
+}
+
+#define T(x) { x, #x }
+struct dmem_test {
+	int (*fn)(const char *root);
+	const char *name;
+} tests[] = {
+	T(test_dmem_max),
+	T(test_dmem_alloc_byte_granularity),
+};
+#undef T
+
+int main(int argc, char **argv)
+{
+	char root[PATH_MAX];
+	struct stat st;
+	int i;
+
+	ksft_print_header();
+
+	if (cg_find_unified_root(root, sizeof(root), NULL))
+		ksft_exit_skip("cgroup v2 isn't mounted\n");
+
+	if (cg_read_strstr(root, "cgroup.controllers", "dmem"))
+		ksft_exit_skip("dmem controller isn't available (CONFIG_CGROUP_DMEM?)\n");
+
+	if (cg_read_strstr(root, "cgroup.subtree_control", "dmem"))
+		if (cg_write(root, "cgroup.subtree_control", "+dmem"))
+			ksft_exit_skip("Failed to enable dmem controller\n");
+
+	if (stat(DM_SELFTEST_ALLOC, &st) < 0)
+		ksft_exit_skip(
+			"dmem_selftest helper not loaded (insmod test_modules/dmem_selftest.ko)\n");
+
+	if (dmem_read_limit(root, "dmem.capacity") < 0)
+		ksft_exit_skip("dmem_selftest region not registered\n");
+
+	ksft_set_plan(ARRAY_SIZE(tests));
+
+	for (i = 0; i < ARRAY_SIZE(tests); i++) {
+		switch (tests[i].fn(root)) {
+		case KSFT_PASS:
+			ksft_test_result_pass("%s\n", tests[i].name);
+			break;
+		default:
+			ksft_test_result_fail("%s\n", tests[i].name);
+			break;
+		}
+	}
+
+	ksft_finished();
+}

-- 
2.55.0