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

[Nhat Pham <nphamcs@gmail.com>]

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>