On Mon, Feb 05, 2024 at 02:56:08PM -0800, Nhat Pham wrote:
> Add a selftest to cover the zswapin code path, allocating more memory
> than the cgroup limit to trigger swapout/zswapout, then reading the
> pages back in memory several times. This is inspired by a recently
> encountered kernel crash on the zswapin path in our internal kernel,
> which went undetected because of a lack of test coverage for this path.
>
> Add a selftest to verify that when memory.zswap.max = 0, no pages can go
> to the zswap pool for the cgroup.
>
> Suggested-by: Rik van Riel <riel@xxxxxxxxxxx>
> Suggested-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
> Signed-off-by: Nhat Pham <nphamcs@xxxxxxxxx>
LGTM with a few nits below:
Acked-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Thanks!
> ---
> tools/testing/selftests/cgroup/test_zswap.c | 120 +++++++++++++++++++-
> 1 file changed, 119 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
> index 32ce975b21d1..c263610a4a60 100644
> --- a/tools/testing/selftests/cgroup/test_zswap.c
> +++ b/tools/testing/selftests/cgroup/test_zswap.c
> @@ -60,6 +60,27 @@ static long get_zswpout(const char *cgroup)
> return cg_read_key_long(cgroup, "memory.stat", "zswpout ");
> }
>
> +static int allocate_and_read_bytes(const char *cgroup, void *arg)
> +{
> + size_t size = (size_t)arg;
> + char *mem = (char *)malloc(size);
> + int ret = 0;
> +
> + if (!mem)
> + return -1;
> + for (int i = 0; i < size; i += 4095)
> + mem[i] = 'a';
> +
> + /* go through the allocated memory to (z)swap in and out pages */
nit: s/go/Go
> + for (int i = 0; i < size; i += 4095) {
> + if (mem[i] != 'a')
> + ret = -1;
> + }
> +
> + free(mem);
> + return ret;
> +}
> +
> static int allocate_bytes(const char *cgroup, void *arg)
> {
> size_t size = (size_t)arg;
> @@ -100,7 +121,6 @@ static int test_zswap_usage(const char *root)
> int ret = KSFT_FAIL;
> char *test_group;
>
> - /* Set up */
We removed this comment here.
> test_group = cg_name(root, "no_shrink_test");
> if (!test_group)
> goto out;
> @@ -133,6 +153,102 @@ static int test_zswap_usage(const char *root)
> return ret;
> }
>
> +/*
> + * Check that when memory.zswap.max = 0, no pages can go to the zswap pool for
> + * the cgroup.
> + */
> +static int test_swapin_nozswap(const char *root)
> +{
> + int ret = KSFT_FAIL;
> + char *test_group;
> + long swap_peak, zswpout;
> +
> + test_group = cg_name(root, "no_zswap_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.zswap.max", "0"))
> + goto out;
> +
> + /* Allocate and read more than memory.max to trigger swapin */
> + if (cg_run(test_group, allocate_and_read_bytes, (void *)MB(32)))
> + goto out;
> +
> + /* Verify that pages are swapped out, but no zswap happened */
> + swap_peak = cg_read_long(test_group, "memory.swap.peak");
> + if (swap_peak < 0) {
> + ksft_print_msg("failed to get cgroup's swap_peak\n");
> + goto out;
> + }
> +
> + if (swap_peak == 0) {
> + ksft_print_msg("pages should be swapped out\n");
> + goto out;
> + }
We can actually check that this number is >= 24M instead. Not a big
deal, but might as well.
> +
> + zswpout = get_zswpout(test_group);
> + if (zswpout < 0) {
> + ksft_print_msg("failed to get zswpout\n");
> + goto out;
> + }
> +
> + if (zswpout > 0) {
> + ksft_print_msg("zswapout > 0 when memory.zswap.max = 0\n");
> + goto out;
> + }
> +
> + ret = KSFT_PASS;
> +
> +out:
> + cg_destroy(test_group);
> + free(test_group);
> + return ret;
> +}
> +
> +/* Simple test to verify the (z)swapin code paths */
> +static int test_zswapin(const char *root)
> +{
> + int ret = KSFT_FAIL;
> + char *test_group;
> + long zswpin;
> +
> + /* Set up */
Yet we added a similar one here :)
> + test_group = cg_name(root, "zswapin_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.zswap.max", "max"))
> + goto out;
> +
> + /* Allocate and read more than memory.max to trigger (z)swap in */
> + if (cg_run(test_group, allocate_and_read_bytes, (void *)MB(32)))
> + goto out;
> +
> + zswpin = cg_read_key_long(test_group, "memory.stat", "zswpin ");
> + if (zswpin < 0) {
> + ksft_print_msg("failed to get zswpin\n");
> + goto out;
> + }
> +
> + if (zswpin == 0) {
> + ksft_print_msg("zswpin should not be 0\n");
> + goto out;
> + }
Same here, we can check that zswpin is at least 24M worth of events.
Again, not a big deal, but might as well.
