[PATCH v4 1/7] selftests/cgroup: skip test_zswap if zswap is globally disabled

Li Wang
2026-03-22T06:11:09Z

test_zswap currently only checks whether zswap is present by testing
/sys/module/zswap. This misses the runtime global state exposed in
/sys/module/zswap/parameters/enabled.

When zswap is built/loaded but globally disabled, the zswap cgroup
selftests run in an invalid environment and may fail spuriously.

Check the runtime enabled state before running the tests:
- skip if zswap is not configured,
- fail if the enabled knob cannot be read,
- skip if zswap is globally disabled.

Also print a hint in the skip message on how to enable zswap.

Signed-off-by: Li Wang <liwang@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Yosry Ahmed <yosry@kernel.org>
---

Notes:
v4:
- No changes.

v3:
- Replace tri-state zswap_enabled() with check_zswap_enabled() for clearer flow.
- Move skip/fail decisions into the helper instead of branching in main().
- Make read failure reporting more explicit by naming
`/sys/module/zswap/parameters/enabled`.
- Keep skip hint for enabling zswap:
`echo 1 > /sys/module/zswap/parameters/enabled`.

v2:
- remove enable/disable_zswap functions
- skip the test if zswap is not enabled
- reporting fail when zswap_enabled return -1

tools/testing/selftests/cgroup/test_zswap.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
index 64ebc3f3f203..e69d845d3592 100644
--- a/tools/testing/selftests/cgroup/test_zswap.c
+++ b/tools/testing/selftests/cgroup/test_zswap.c
@@ -589,9 +589,21 @@ struct zswap_test {
};
#undef T

-static bool zswap_configured(void)
+static void check_zswap_enabled(void)
{
- return access("/sys/module/zswap", F_OK) == 0;
+ char value[2];
+
+ if (access("/sys/module/zswap", F_OK))
+ ksft_exit_skip("zswap isn't configured\n");
+
+ if (read_text("/sys/module/zswap/parameters/enabled", value,
+ sizeof(value)) <= 0)
+ ksft_exit_fail_msg("Failed to read "
+ "/sys/module/zswap/parameters/enabled\n");
+
+ if (value[0] == 'N')
+ ksft_exit_skip("zswap is disabled (hint: echo 1 > "
+ "/sys/module/zswap/parameters/enabled)\n");
}

int main(int argc, char **argv)
@@ -604,8 +616,7 @@ int main(int argc, char **argv)
if (cg_find_unified_root(root, sizeof(root), NULL))
ksft_exit_skip("cgroup v2 isn't mounted\n");

- if (!zswap_configured())
- ksft_exit_skip("zswap isn't configured\n");
+ check_zswap_enabled();

/*
* Check that memory controller is available:
--
2.53.0