Commit 50133c09 authored by Guopeng Zhang's avatar Guopeng Zhang Committed by Tejun Heo
Browse files

selftests: cgroup: Replace sleep with cg_read_key_long_poll() for waiting on nr_dying_descendants 



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: default avatarGuopeng Zhang <zhangguopeng@kylinos.cn>
Reviewed-by: default avatarShakeel Butt <shakeel.butt@linux.dev>
Acked-by: default avatarMichal Koutný <mkoutny@suse.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 6360d444

tools/testing/selftests/cgroup/test_kmem.c

+15 −18
Original line number Diff line number Diff line
@@ -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.

	 * 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.

	 */

		sleep(1);

		if (i > 5)

			printf("Waiting time longer than 5s; wait: %ds (dead: %ld)\n", i, dead);

	}

	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);