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

[R Nageswara Sastry <rnsastry@linux.ibm.com>]

On 31.08.2026 6:55 PM, Albert Esteve wrote:
> 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>
Tested-by: R Nageswara Sastry <rnsastry@linux.ibm.com>

System: ppc64le LPAR (IBM POWER), Linux 7.3-rc2

# insmod test_modules/dmem_selftest.ko
# ./test_dmem
TAP version 13
1..2
ok 1 test_dmem_max
ok 2 test_dmem_alloc_byte_granularity
# Totals: pass:2 fail:0 xfail:0 xpass:0 skip:0 error:0

> ---
>   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();
> +}
>
-- 
Thanks and Regards
R.Nageswara Sastry