Replace the manual sleep-and-retry logic in test_kmem_dead_cgroups() with the new helper `cg_read_key_long_poll()`. This change improves the robustness of the test by polling the "nr_dying_descendants" counter in `cgroup.stat` until it reaches 0 or the timeout is exceeded.
Additionally, increase the retry timeout to 8 seconds (from 5 seconds) based on testing results: - With 5-second timeout: 4/20 runs passed. - With 8-second timeout: 20/20 runs passed. The 8 second timeout is based on stress testing of test_kmem_dead_cgroups() under load: 5 seconds was occasionally not enough for reclaim of dying descendants to complete, whereas 8 seconds consistently covered the observed latencies. This value is intended as a generous upper bound for the asynchronous reclaim and is not tied to any specific kernel constant, so it can be adjusted in the future if reclaim behavior changes. Signed-off-by: Guopeng Zhang <[email protected]> Reviewed-by: Shakeel Butt <[email protected]> --- tools/testing/selftests/cgroup/test_kmem.c | 33 ++++++++++------------ 1 file changed, 15 insertions(+), 18 deletions(-) diff --git a/tools/testing/selftests/cgroup/test_kmem.c b/tools/testing/selftests/cgroup/test_kmem.c index ca38525484e3..eeabd34bf083 100644 --- a/tools/testing/selftests/cgroup/test_kmem.c +++ b/tools/testing/selftests/cgroup/test_kmem.c @@ -26,6 +26,7 @@ */ #define MAX_VMSTAT_ERROR (4096 * 64 * get_nprocs()) +#define KMEM_DEAD_WAIT_RETRIES 80 static int alloc_dcache(const char *cgroup, void *arg) { @@ -306,9 +307,7 @@ static int test_kmem_dead_cgroups(const char *root) { int ret = KSFT_FAIL; char *parent; - long dead; - int i; - int max_time = 20; + long dead = -1; parent = cg_name(root, "kmem_dead_cgroups_test"); if (!parent) @@ -323,21 +322,19 @@ static int test_kmem_dead_cgroups(const char *root) if (cg_run_in_subcgroups(parent, alloc_dcache, (void *)100, 30)) goto cleanup; - for (i = 0; i < max_time; i++) { - dead = cg_read_key_long(parent, "cgroup.stat", - "nr_dying_descendants "); - if (dead == 0) { - ret = KSFT_PASS; - break; - } - /* - * Reclaiming cgroups might take some time, - * let's wait a bit and repeat. - */ - sleep(1); - if (i > 5) - printf("Waiting time longer than 5s; wait: %ds (dead: %ld)\n", i, dead); - } + /* + * Allow up to ~8s for reclaim of dying descendants to complete. + * This is a generous upper bound derived from stress testing, not + * from a specific kernel constant, and can be adjusted if reclaim + * behavior changes in the future. + */ + dead = cg_read_key_long_poll(parent, "cgroup.stat", + "nr_dying_descendants ", 0, KMEM_DEAD_WAIT_RETRIES, + DEFAULT_WAIT_INTERVAL_US); + if (dead) + goto cleanup; + + ret = KSFT_PASS; cleanup: cg_destroy(parent); -- 2.25.1
