From a549f9f31561a569e3c7a4cb6226a0b31d35fc89 Mon Sep 17 00:00:00 2001 From: Domenico Cerasuolo Date: Wed, 21 Jun 2023 17:35:47 +0200 Subject: selftests: cgroup: add test_zswap with no kmem bypass test Add a cgroup selftest that verifies memcg charging in zswap. The original issue was that kmem bypass was applied to pages swapped out to zswap by kswapd, resulting in zswapped memory not being charged. It was fixed by commit cd08d80ecdac("mm: correctly charge compressed memory to its memcg"). Link: https://lkml.kernel.org/r/20230621153548.428093-3-cerasuolodomenico@gmail.com Signed-off-by: Domenico Cerasuolo Cc: Dan Streetman Cc: Johannes Weiner Cc: Michal Hocko Cc: Muchun Song Cc: Nhat Pham Cc: Rik van Riel Cc: Roman Gushchin Cc: Seth Jennings Cc: Shakeel Butt Cc: Shuah Khan Cc: Tejun Heo Cc: Vitaly Wool Cc: Zefan Li Signed-off-by: Andrew Morton --- tools/testing/selftests/cgroup/test_zswap.c | 163 ++++++++++++++++++++++++++++ 1 file changed, 163 insertions(+) (limited to 'tools/testing/selftests/cgroup') diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c index 001533667322..e859fecd310b 100644 --- a/tools/testing/selftests/cgroup/test_zswap.c +++ b/tools/testing/selftests/cgroup/test_zswap.c @@ -4,15 +4,178 @@ #include #include #include +#include +#include +#include +#include +#include #include "../kselftest.h" #include "cgroup_util.h" +static int read_int(const char *path, size_t *value) +{ + FILE *file; + int ret = 0; + + file = fopen(path, "r"); + if (!file) + return -1; + if (fscanf(file, "%ld", value) != 1) + ret = -1; + fclose(file); + return ret; +} + +static int set_min_free_kb(size_t value) +{ + FILE *file; + int ret; + + file = fopen("/proc/sys/vm/min_free_kbytes", "w"); + if (!file) + return -1; + ret = fprintf(file, "%ld\n", value); + fclose(file); + return ret; +} + +static int read_min_free_kb(size_t *value) +{ + return read_int("/proc/sys/vm/min_free_kbytes", value); +} + +static int get_zswap_stored_pages(size_t *value) +{ + return read_int("/sys/kernel/debug/zswap/stored_pages", value); +} + +struct no_kmem_bypass_child_args { + size_t target_alloc_bytes; + size_t child_allocated; +}; + +static int no_kmem_bypass_child(const char *cgroup, void *arg) +{ + struct no_kmem_bypass_child_args *values = arg; + void *allocation; + + allocation = malloc(values->target_alloc_bytes); + if (!allocation) { + values->child_allocated = true; + return -1; + } + for (long i = 0; i < values->target_alloc_bytes; i += 4095) + ((char *)allocation)[i] = 'a'; + values->child_allocated = true; + pause(); + free(allocation); + return 0; +} + +/* + * When pages owned by a memcg are pushed to zswap by kswapd, they should be + * charged to that cgroup. This wasn't the case before commit + * cd08d80ecdac("mm: correctly charge compressed memory to its memcg"). + * + * The test first allocates memory in a memcg, then raises min_free_kbytes to + * a very high value so that the allocation falls below low wm, then makes + * another allocation to trigger kswapd that should push the memcg-owned pages + * to zswap and verifies that the zswap pages are correctly charged. + * + * To be run on a VM with at most 4G of memory. + */ +static int test_no_kmem_bypass(const char *root) +{ + size_t min_free_kb_high, min_free_kb_low, min_free_kb_original; + struct no_kmem_bypass_child_args *values; + size_t trigger_allocation_size; + int wait_child_iteration = 0; + long stored_pages_threshold; + struct sysinfo sys_info; + int ret = KSFT_FAIL; + int child_status; + char *test_group; + pid_t child_pid; + + /* Read sys info and compute test values accordingly */ + if (sysinfo(&sys_info) != 0) + return KSFT_FAIL; + if (sys_info.totalram > 5000000000) + return KSFT_SKIP; + values = mmap(0, sizeof(struct no_kmem_bypass_child_args), PROT_READ | + PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0); + if (values == MAP_FAILED) + return KSFT_FAIL; + if (read_min_free_kb(&min_free_kb_original)) + return KSFT_FAIL; + min_free_kb_high = sys_info.totalram / 2000; + min_free_kb_low = sys_info.totalram / 500000; + values->target_alloc_bytes = (sys_info.totalram - min_free_kb_high * 1000) + + sys_info.totalram * 5 / 100; + stored_pages_threshold = sys_info.totalram / 5 / 4096; + trigger_allocation_size = sys_info.totalram / 20; + + /* Set up test memcg */ + if (cg_write(root, "cgroup.subtree_control", "+memory")) + goto out; + test_group = cg_name(root, "kmem_bypass_test"); + if (!test_group) + goto out; + + /* Spawn memcg child and wait for it to allocate */ + set_min_free_kb(min_free_kb_low); + if (cg_create(test_group)) + goto out; + values->child_allocated = false; + child_pid = cg_run_nowait(test_group, no_kmem_bypass_child, values); + if (child_pid < 0) + goto out; + while (!values->child_allocated && wait_child_iteration++ < 10000) + usleep(1000); + + /* Try to wakeup kswapd and let it push child memory to zswap */ + set_min_free_kb(min_free_kb_high); + for (int i = 0; i < 20; i++) { + size_t stored_pages; + char *trigger_allocation = malloc(trigger_allocation_size); + + if (!trigger_allocation) + break; + for (int i = 0; i < trigger_allocation_size; i += 4095) + trigger_allocation[i] = 'b'; + usleep(100000); + free(trigger_allocation); + if (get_zswap_stored_pages(&stored_pages)) + break; + if (stored_pages < 0) + break; + /* If memory was pushed to zswap, verify it belongs to memcg */ + if (stored_pages > stored_pages_threshold) { + int zswapped = cg_read_key_long(test_group, "memory.stat", "zswapped "); + int delta = stored_pages * 4096 - zswapped; + int result_ok = delta < stored_pages * 4096 / 4; + + ret = result_ok ? KSFT_PASS : KSFT_FAIL; + break; + } + } + + kill(child_pid, SIGTERM); + waitpid(child_pid, &child_status, 0); +out: + set_min_free_kb(min_free_kb_original); + cg_destroy(test_group); + free(test_group); + return ret; +} + #define T(x) { x, #x } struct zswap_test { int (*fn)(const char *root); const char *name; } tests[] = { + T(test_no_kmem_bypass), }; #undef T -- cgit v1.2.3