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

Nhat Pham
2026-03-27T18:21:39Z

On Sun, Mar 22, 2026 at 2:11 AM Li Wang <liwang@redhat.com> wrote:
>
> 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
>

LGTM with Yosry's suggestion. If there's no other change you can also
submit a fixlet I guess?

With that:

Acked-by: Nhat Pham <nphamcs@gmail.com>