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@surriel.com Suggested-by: Yosry Ahmed yosryahmed@google.com Signed-off-by: Nhat Pham nphamcs@gmail.com --- 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 */ + 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 */ 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; + } + + 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 */ + 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; + } + + ret = KSFT_PASS; + +out: + cg_destroy(test_group); + free(test_group); + return ret; +} + /* * 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 @@ -309,6 +425,8 @@ struct zswap_test { const char *name; } tests[] = { T(test_zswap_usage), + T(test_swapin_nozswap), + T(test_zswapin), T(test_no_kmem_bypass), T(test_no_invasive_cgroup_shrink), };