On Mon, Aug 24, 2026 at 8:28 PM Michal Koutný <[email protected]> wrote:
>
> On Mon, Jul 06, 2026 at 02:06:41PM +0200, Albert Esteve <[email protected]>
> wrote:
> > +static long long dmem_read_limit_for_region(const char *cgroup, const char
> > *ctrl,
> > + const char *region_name)
>
> This should be replaceable with lib/cgroup_util.c:cg_read_key_long()
True. I'll take care of it.
>
> > +{
> > + char buf[4096];
> > + char *line, *saveptr = NULL;
> > + char fname[256];
> > + char fval[64];
> > +
> > + if (cg_read(cgroup, ctrl, buf, sizeof(buf)) < 0)
> > + return -2;
> > +
> > + for (line = strtok_r(buf, "\n", &saveptr); line;
> > + line = strtok_r(NULL, "\n", &saveptr)) {
> > + if (!line[0])
> > + continue;
> > + if (sscanf(line, "%255s %63s", fname, fval) != 2)
> > + continue;
> > + if (strcmp(fname, region_name))
> > + continue;
> > + if (!strcmp(fval, "max"))
> > + return -1;
> > + return strtoll(fval, NULL, 0);
> > + }
> > + return -2;
> > +}
> > +
> > +static long long dmem_read_limit(const char *cgroup, const char *ctrl)
> > +{
> > + return dmem_read_limit_for_region(cgroup, ctrl, DM_SELFTEST_REGION);
> > +}
> > +
> > +static int dmem_write_limit(const char *cgroup, const char *ctrl,
> > + const char *val)
> > +{
> > + char wr[512];
> > +
> > + snprintf(wr, sizeof(wr), "%s %s", DM_SELFTEST_REGION, val);
> > + return cg_write(cgroup, ctrl, wr);
> > +}
> > +
> > +static int dmem_selftest_charge_bytes(unsigned long long bytes)
> > +{
> > + char wr[32];
> > +
> > + snprintf(wr, sizeof(wr), "%llu", bytes);
> > + return write_text(DM_SELFTEST_CHARGE, wr, strlen(wr));
> > +}
> > +
> > +static int dmem_selftest_uncharge(void)
> > +{
> > + return write_text(DM_SELFTEST_UNCHARGE, "\n", 1);
> > +}
> > +
> > +/*
> > + * First, this test creates the following hierarchy:
> > + * A
> > + * A/B dmem.max=1M
> > + * A/B/C dmem.max=75K
> > + * A/B/D dmem.max=25K
> > + * A/B/E dmem.max=8K
> > + * A/B/F dmem.max=0
> > + *
> > + * Then for each leaf cgroup it tries to charge above dmem.max
> > + * and expects the charge request to fail and dmem.current to
> > + * remain unchanged.
> > + *
> > + * For leaves with non-zero dmem.max, it additionally charges a
> > + * smaller amount and verifies accounting grows within one PAGE_SIZE
> > + * rounding bound, then uncharges and verifies dmem.current returns
> > + * to the previous value.
> > + *
> > + */
> > +static int test_dmem_max(const char *root)
> > +{
> > + static const char * const leaf_max[] = { "75K", "25K", "8K", "0" };
> > + static const unsigned long long fail_sz[] = {
> > + (75ULL * 1024ULL) + 1ULL,
> > + (25ULL * 1024ULL) + 1ULL,
> > + (8ULL * 1024ULL) + 1ULL,
> > + 1ULL
> > + };
> > + static const unsigned long long pass_sz[] = {
> > + 4096ULL, 4096ULL, 4096ULL, 0ULL
> > + };
>
> Possibly those could be signed (to save the casts down below).
>
> > + char *parent[2] = {NULL};
> > + char *children[4] = {NULL};
> > + unsigned long long cap;
> > + long long page_size;
> > + long long cur_before, cur_after;
>
> Just `long` should be fine (with gcc).
>
> > + int ret = KSFT_FAIL;
> > + int charged = 0;
> > + int in_child = 0;
> > + long long v;
> > + int i;
> > +
> > + if (access(DM_SELFTEST_CHARGE, W_OK) != 0)
> > + return KSFT_SKIP;
> > +
> > + if (find_selftest_region(root, &cap) != 1)
> > + return KSFT_SKIP;
> > +
> > + page_size = sysconf(_SC_PAGESIZE);
> > + if (page_size <= 0)
> > + goto cleanup;
> > +
> > + 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 < 4; i++) {
>
> 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", "1M"))
> > + goto cleanup;
> > + for (i = 0; i < 4; i++)
>
> 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 != 1024LL * 1024LL)
>
> This...
>
> > + goto cleanup;
> > + v = dmem_read_limit(children[0], "dmem.max");
> > + if (v != 75LL * 1024LL)
>
> ...and these literals would be nicer with MB() macro and possibly added
> similar KB() macro.
>
> > + goto cleanup;
> > + v = dmem_read_limit(children[1], "dmem.max");
> > + if (v != 25LL * 1024LL)
> > + goto cleanup;
> > + v = dmem_read_limit(children[2], "dmem.max");
> > + if (v != 8LL * 1024LL)
> > + goto cleanup;
> > + v = dmem_read_limit(children[3], "dmem.max");
> > + if (v != 0)
> > + goto cleanup;
> > +
> > + for (i = 0; i < 4; i++) {
>
> for (i = 0; i < ARRAY_SIZE(children); i++) {
>
> (to avoid unnamed non-trivial constant)
>
> > + 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_charge_bytes(fail_sz[i]) >= 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_charge_bytes(pass_sz[i]) < 0)
> > + goto cleanup;
> > + charged = 1;
> > +
> > + cur_after = dmem_read_limit(children[i],
> > "dmem.current");
> > + if (cur_after < cur_before + (long long)pass_sz[i])
> > + goto cleanup;
> > + if (cur_after > cur_before + (long long)pass_sz[i] +
> > page_size)
> > + goto cleanup;
> > +
> > + if (dmem_selftest_uncharge() < 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_uncharge();
> > + if (in_child)
> > + cg_enter_current(root);
> > + for (i = 3; i >= 0; i--) {
>
> ditto with ARRAY_SIZE
>
> > + if (!children[i])
> > + continue;
> > + cg_destroy(children[i]);
> > + free(children[i]);
> > + }
> > + for (i = 1; i >= 0; i--) {
>
> ditto with ARRAY_SIZE
I'll address all the points raised (here and all the above).
>
> > + if (!parent[i])
> > + continue;
> > + cg_destroy(parent[i]);
> > + free(parent[i]);
> > + }
> > + return ret;
> > +}
> > +
> > +/*
> > + * This test sets dmem.min and dmem.low on a child cgroup, then charge
> > + * from that context and verify dmem.current tracks the charged bytes
> > + * (within one page rounding).
>
> I don't know, this doesn't test much of the .min nor .low protection,
> and the .current tracking is already tested by the above. I'd drop it
> for now.
Makes sense. I'll do that for the next version.
>
> > + */
> > +static int test_dmem_charge_with_attr(const char *root, bool min)
> > +{
> > + unsigned long long cap;
> > + const unsigned long long charge_sz = 12345ULL;
> > + const char *attribute = min ? "dmem.min" : "dmem.low";
> > + int ret = KSFT_FAIL;
> > + char *cg = NULL;
> > + long long cur;
> > + long long page_size;
> > + int charged = 0;
> > + int in_child = 0;
> > +
> > + if (access(DM_SELFTEST_CHARGE, W_OK) != 0)
> > + return KSFT_SKIP;
> > +
> > + if (find_selftest_region(root, &cap) != 1)
> > + return KSFT_SKIP;
> > +
> > + page_size = sysconf(_SC_PAGESIZE);
> > + if (page_size <= 0)
> > + goto cleanup;
> > +
> > + cg = cg_name(root, "test_dmem_attr");
> > + if (!cg)
> > + goto cleanup;
> > +
> > + if (cg_create(cg))
> > + goto cleanup;
> > +
> > + if (cg_enter_current(cg))
> > + goto cleanup;
> > + in_child = 1;
> > +
> > + if (dmem_write_limit(cg, attribute, "16K"))
> > + goto cleanup;
> > +
> > + if (dmem_selftest_charge_bytes(charge_sz) < 0)
> > + goto cleanup;
> > + charged = 1;
> > +
> > + cur = dmem_read_limit(cg, "dmem.current");
> > + if (cur < (long long)charge_sz)
> > + goto cleanup;
> > + if (cur > (long long)charge_sz + page_size)
> > + goto cleanup;
> > +
> > + if (dmem_selftest_uncharge() < 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_uncharge();
> > + if (in_child)
> > + cg_enter_current(root);
> > + cg_destroy(cg);
> > + free(cg);
> > + return ret;
> > +}
> > +
> > +static int test_dmem_min(const char *root)
> > +{
> > + return test_dmem_charge_with_attr(root, true);
> > +}
> > +
> > +static int test_dmem_low(const char *root)
> > +{
> > + return test_dmem_charge_with_attr(root, false);
> > +}
> > +
> > +/*
> > + * This test charges non-page-aligned byte sizes and verify dmem.current
> > + * stays consistent: it must account at least the requested bytes and
> > + * never exceed one kernel page of rounding overhead. Then uncharge must
> > + * return usage to 0.
>
> The lower bound makes sense. Could you explain more about the upper
> bound and granularity? That applies only for the test module or is that
> intended constraint for any dmem-charging driver?
Uhm, the upper bound was modeled on test_memcontrol.c. Those tests
cannot match memory.current exactly, so use lower bound plus
values_close().
But for dmem, it isn't necessary; it accounts for the requested size
with no page rounding or extra charge. I'll fix that and check for
equality.
Thanks for raising this.
>
> > + */
> > +static int test_dmem_charge_byte_granularity(const char *root)
> > +{
> > + static const unsigned long long sizes[] = { 1ULL, 4095ULL, 4097ULL,
> > 12345ULL };
> > + char *cg = NULL;
> > + unsigned long long cap;
> > + long long cur;
> > + long long page_size;
> > + int ret = KSFT_FAIL;
> > + int charged = 0;
> > + int in_child = 0;
> > + size_t i;
> > +
> > + if (access(DM_SELFTEST_CHARGE, W_OK) != 0)
> > + return KSFT_SKIP;
> > +
> > + if (find_selftest_region(root, &cap) != 1)
> > + return KSFT_SKIP;
> > +
> > + page_size = sysconf(_SC_PAGESIZE);
> > + if (page_size <= 0)
> > + goto cleanup;
> > +
> > + 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", "8M"))
> > + goto cleanup;
> > +
> > + if (cg_enter_current(cg))
> > + goto cleanup;
> > + in_child = 1;
> > +
> > + for (i = 0; i < ARRAY_SIZE(sizes); i++) {
> > + if (dmem_selftest_charge_bytes(sizes[i]) < 0)
> > + goto cleanup;
> > + charged = 1;
> > +
> > + cur = dmem_read_limit(cg, "dmem.current");
> > + if (cur < (long long)sizes[i])
> > + goto cleanup;
> > + if (cur > (long long)sizes[i] + page_size)
> > + goto cleanup;
> > +
> > + if (dmem_selftest_uncharge() < 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_uncharge();
> > + 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_min),
> > + T(test_dmem_low),
> > + T(test_dmem_charge_byte_granularity),
> > +};
> > +#undef T
> > +
> > +int main(int argc, char **argv)
> > +{
> > + char root[PATH_MAX];
> > + int i;
> > +
> > + ksft_print_header();
> > + ksft_set_plan(ARRAY_SIZE(tests));
> > +
> > + 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");
> > +
> > + 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;
> > + case KSFT_SKIP:
> > + ksft_test_result_skip(
> > + "%s (need CONFIG_DMEM_SELFTEST, modprobe
> > dmem_selftest)\n",
> > + tests[i].name);
>
> I'm worried that the KSFT_SKIP from a subtest might be too broad for the
> modprobe prompt.
> Perhaps you can check it by stat'ing DM_SELFTEST_CHARGE before any
> subtests start?
Agreed. I'll stat the helper in main().
BR,
Albert.
>
>
> > + break;
> > + default:
> > + ksft_test_result_fail("%s\n", tests[i].name);
> > + break;
> > + }
> > + }
> > +
> > + ksft_finished();
> > +}
> >
> > --
> > 2.54.0
> >
