Re: [PATCH v3 4/5] selftests: cgroup: update per-memcg zswap writeback selftest

[Nhat Pham <nphamcs@gmail.com>]

On Tue, Oct 17, 2023 at 4:21 PM Nhat Pham <nphamcs@gmail.com> wrote:
>
> From: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
>
> The memcg-zswap self test is updated to adjust to the behavior change
> implemented by commit 87730b165089 ("zswap: make shrinking memcg-aware"),
> where zswap performs writeback for specific memcg.
>
> Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
> Signed-off-by: Nhat Pham <nphamcs@gmail.com>

/s/Signed-off/Acked
This is Domenico's work :) I used the wrong tag here. Should be:
Acked-by: Nhat Pham <nphamcs@gmail.com>

> ---
>  tools/testing/selftests/cgroup/test_zswap.c | 74 ++++++++++++++-------
>  1 file changed, 50 insertions(+), 24 deletions(-)
>
> diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
> index 49def87a909b..11271fabeffc 100644
> --- a/tools/testing/selftests/cgroup/test_zswap.c
> +++ b/tools/testing/selftests/cgroup/test_zswap.c
> @@ -50,9 +50,9 @@ static int get_zswap_stored_pages(size_t *value)
>         return read_int("/sys/kernel/debug/zswap/stored_pages", value);
>  }
>
> -static int get_zswap_written_back_pages(size_t *value)
> +static int get_cg_wb_count(const char *cg)
>  {
> -       return read_int("/sys/kernel/debug/zswap/written_back_pages", value);
> +       return cg_read_key_long(cg, "memory.stat", "zswap_wb");
>  }
>
>  static int allocate_bytes(const char *cgroup, void *arg)
> @@ -68,45 +68,71 @@ static int allocate_bytes(const char *cgroup, void *arg)
>         return 0;
>  }
>
> +static char *setup_test_group_1M(const char *root, const char *name)
> +{
> +       char *group_name = cg_name(root, name);
> +
> +       if (!group_name)
> +               return NULL;
> +       if (cg_create(group_name))
> +               goto fail;
> +       if (cg_write(group_name, "memory.max", "1M")) {
> +               cg_destroy(group_name);
> +               goto fail;
> +       }
> +       return group_name;
> +fail:
> +       free(group_name);
> +       return NULL;
> +}
> +
>  /*
>   * When trying to store a memcg page in zswap, if the memcg hits its memory
> - * limit in zswap, writeback should not be triggered.
> - *
> - * This was fixed with commit 0bdf0efa180a("zswap: do not shrink if cgroup may
> - * not zswap"). Needs to be revised when a per memcg writeback mechanism is
> - * implemented.
> + * limit in zswap, writeback should affect only the zswapped pages of that
> + * memcg.
>   */
>  static int test_no_invasive_cgroup_shrink(const char *root)
>  {
> -       size_t written_back_before, written_back_after;
>         int ret = KSFT_FAIL;
> -       char *test_group;
> +       size_t control_allocation_size = MB(10);
> +       char *control_allocation, *wb_group = NULL, *control_group = NULL;
>
>         /* Set up */
> -       test_group = cg_name(root, "no_shrink_test");
> -       if (!test_group)
> -               goto out;
> -       if (cg_create(test_group))
> +       wb_group = setup_test_group_1M(root, "per_memcg_wb_test1");
> +       if (!wb_group)
> +               return KSFT_FAIL;
> +       if (cg_write(wb_group, "memory.zswap.max", "10K"))
>                 goto out;
> -       if (cg_write(test_group, "memory.max", "1M"))
> +       control_group = setup_test_group_1M(root, "per_memcg_wb_test2");
> +       if (!control_group)
>                 goto out;
> -       if (cg_write(test_group, "memory.zswap.max", "10K"))
> +
> +       /* Push some test_group2 memory into zswap */
> +       if (cg_enter_current(control_group))
>                 goto out;
> -       if (get_zswap_written_back_pages(&written_back_before))
> +       control_allocation = malloc(control_allocation_size);
> +       for (int i = 0; i < control_allocation_size; i += 4095)
> +               control_allocation[i] = 'a';
> +       if (cg_read_key_long(control_group, "memory.stat", "zswapped") < 1)
>                 goto out;
>
> -       /* Allocate 10x memory.max to push memory into zswap */
> -       if (cg_run(test_group, allocate_bytes, (void *)MB(10)))
> +       /* Allocate 10x memory.max to push wb_group memory into zswap and trigger wb */
> +       if (cg_run(wb_group, allocate_bytes, (void *)MB(10)))
>                 goto out;
>
> -       /* Verify that no writeback happened because of the memcg allocation */
> -       if (get_zswap_written_back_pages(&written_back_after))
> -               goto out;
> -       if (written_back_after == written_back_before)
> +       /* Verify that only zswapped memory from gwb_group has been written back */
> +       if (get_cg_wb_count(wb_group) > 0 && get_cg_wb_count(control_group) == 0)
>                 ret = KSFT_PASS;
>  out:
> -       cg_destroy(test_group);
> -       free(test_group);
> +       cg_enter_current(root);
> +       if (control_group) {
> +               cg_destroy(control_group);
> +               free(control_group);
> +       }
> +       cg_destroy(wb_group);
> +       free(wb_group);
> +       if (control_allocation)
> +               free(control_allocation);
>         return ret;
>  }
>
> --
> 2.34.1