Re: [PATCH v8 5/6] selftests: cgroup: update per-memcg zswap writeback selftest

Chris Li
2023-12-08T00:43:35Z

Hi Nhat,

Thanks for the self test.

Acked-by: Chris Li <chrisl@kernel.org> (Google)

Chris

On Thu, Nov 30, 2023 at 11:40 AM 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>
> ---
> 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 c99d2adaca3f..47fdaa146443 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", "zswp_wb");
> }
>
> static long get_zswpout(const char *cgroup)
> @@ -73,6 +73,24 @@ 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;
> +}
> +
> /*
> * Sanity test to check that pages are written into zswap.
> */
> @@ -117,43 +135,51 @@ static int test_zswap_usage(const char *root)
>
> /*
> * 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
>