Re: [PATCH] selftests: cgroup: add tests to verify the zswap writeback path

[Usama Arif]

On 01/05/2024 11:04, Usama Arif wrote:
> The condition for writeback can be triggered by allocating random
> memory more than memory.high to push memory into zswap, more than
> zswap.max to trigger writeback if enabled, but less than memory.max
> so that OOM is not triggered. Both values of memory.zswap.writeback
> are tested.
>
> Signed-off-by: Usama Arif <usamaarif642@xxxxxxxxx>


Forgot to add:

Suggested-by: Nhat Pham <nphamcs@xxxxxxxxx>


> ---
>   tools/testing/selftests/cgroup/test_zswap.c | 83 +++++++++++++++++++++
>   1 file changed, 83 insertions(+)
>
> diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
> index f0e488ed90d8..fe0e7221525c 100644
> --- a/tools/testing/selftests/cgroup/test_zswap.c
> +++ b/tools/testing/selftests/cgroup/test_zswap.c
> @@ -94,6 +94,19 @@ static int allocate_bytes(const char *cgroup, void *arg)
>   	return 0;
>   }
>   
> +static int allocate_random_bytes(const char *cgroup, void *arg)
> +{
> +	size_t size = (size_t)arg;
> +	char *mem = (char *)malloc(size);
> +
> +	if (!mem)
> +		return -1;
> +	for (int i = 0; i < size; i++)
> +		mem[i] = rand() % 128;
> +	free(mem);
> +	return 0;
> +}
> +
>   static char *setup_test_group_1M(const char *root, const char *name)
>   {
>   	char *group_name = cg_name(root, name);
> @@ -248,6 +261,74 @@ static int test_zswapin(const char *root)
>   	return ret;
>   }
>   
> +/* Test to verify the zswap writeback path */
> +static int test_zswap_writeback(const char *root, bool wb)
> +{
> +	int ret = KSFT_FAIL;
> +	char *test_group;
> +	long zswpwb_before, zswpwb_after;
> +
> +	test_group = cg_name(root,
> +		wb ? "zswap_writeback_enabled_test" : "zswap_writeback_disabled_test");
> +	if (!test_group)
> +		goto out;
> +	if (cg_create(test_group))
> +		goto out;
> +	if (cg_write(test_group, "memory.max", "8M"))
> +		goto out;
> +	if (cg_write(test_group, "memory.high", "2M"))
> +		goto out;
> +	if (cg_write(test_group, "memory.zswap.max", "2M"))
> +		goto out;
> +	if (cg_write(test_group, "memory.zswap.writeback", wb ? "1" : "0"))
> +		goto out;
> +
> +	zswpwb_before = cg_read_key_long(test_group, "memory.stat", "zswpwb ");
> +	if (zswpwb_before < 0) {
> +		ksft_print_msg("failed to get zswpwb_before\n");
> +		goto out;
> +	}
> +
> +	/*
> +	 * Allocate more than memory.high to push memory into zswap,
> +	 * more than zswap.max to trigger writeback if enabled,
> +	 * but less than memory.max so that OOM is not triggered
> +	 */
> +	if (cg_run(test_group, allocate_random_bytes, (void *)MB(3)))
> +		goto out;
> +
> +	/* Verify that zswap writeback occurred only if writeback was enabled */
> +	zswpwb_after = cg_read_key_long(test_group, "memory.stat", "zswpwb ");
> +	if (wb) {
> +		if (zswpwb_after <= zswpwb_before) {
> +			ksft_print_msg("writeback enabled and zswpwb_after <= zswpwb_before\n");
> +			goto out;
> +		}
> +	} else {
> +		if (zswpwb_after != zswpwb_before) {
> +			ksft_print_msg("writeback disabled and zswpwb_after != zswpwb_before\n");
> +			goto out;
> +		}
> +	}
> +
> +	ret = KSFT_PASS;
> +
> +out:
> +	cg_destroy(test_group);
> +	free(test_group);
> +	return ret;
> +}
> +
> +static int test_zswap_writeback_enabled(const char *root)
> +{
> +	return test_zswap_writeback(root, true);
> +}
> +
> +static int test_zswap_writeback_disabled(const char *root)
> +{
> +	return test_zswap_writeback(root, false);
> +}
> +
>   /*
>    * When trying to store a memcg page in zswap, if the memcg hits its memory
>    * limit in zswap, writeback should affect only the zswapped pages of that
> @@ -425,6 +506,8 @@ struct zswap_test {
>   	T(test_zswap_usage),
>   	T(test_swapin_nozswap),
>   	T(test_zswapin),
> +	T(test_zswap_writeback_enabled),
> +	T(test_zswap_writeback_disabled),
>   	T(test_no_kmem_bypass),
>   	T(test_no_invasive_cgroup_shrink),
>   };