[PATCH v4 6/7] selftest/cgroup: fix zswap test_no_invasive_cgroup_shrink on large pagesize system

Li Wang
2026-03-22T06:11:43Z

test_no_invasive_cgroup_shrink uses fixed zswap/memory limits and
allocation sizes that are too small on systems with large PAGE_SIZE
(e.g. 64K). In that case, the test may fail to build enough pressure
to trigger zswap writeback reliably, leading to false failures.

Make the test size parameters PAGE_SIZE-aware and consistent:
- set control_allocation_size to PAGE_SIZE * 1024,
- set memory.zswap.max to PAGE_SIZE,
- set memory.max of both cgroups to control_allocation_size / 2,
- allocate control_allocation_size in wb_group (2x memory.max).

This keeps the test behavior stable across 4K and 64K PAGE_SIZE
configurations and avoids spurious failures in
test_no_invasive_cgroup_shrink.

=== Error Log ===
# getconf PAGESIZE
65536

# ./test_zswap
TAP version 13
...
ok 5 test_zswap_writeback_disabled
ok 6 # SKIP test_no_kmem_bypass
not ok 7 test_no_invasive_cgroup_shrink

Signed-off-by: Li Wang <liwang@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Yosry Ahmed <yosryahmed@google.com>
---

Notes:
v4:
- Use use %zu in print pagesize format.
v3:
- Make PAGE_SIZE aware instead of using fixed sizing.
- Set memory.max for wb_group/control_group to control_allocation_size/2.
- Update wb_group pressure allocation to control_allocation_size.
- Clarify commit message to focus on this test's sizing issue.
v2:
- No change.

tools/testing/selftests/cgroup/test_zswap.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
index 407cfb6ae34d..ec7f0bd515e1 100644
--- a/tools/testing/selftests/cgroup/test_zswap.c
+++ b/tools/testing/selftests/cgroup/test_zswap.c
@@ -421,17 +421,26 @@ static int test_zswap_writeback_disabled(const char *root)
static int test_no_invasive_cgroup_shrink(const char *root)
{
int ret = KSFT_FAIL;
- size_t control_allocation_size = MB(10);
+ size_t control_allocation_size = pagesize * 1024;
+ char zswap_max_buf[32], mem_max_buf[32];
char *control_allocation = NULL, *wb_group = NULL, *control_group = NULL;

+ snprintf(zswap_max_buf, sizeof(zswap_max_buf), "%zu", pagesize);
+ snprintf(mem_max_buf, sizeof(mem_max_buf), "%zu", control_allocation_size / 2);
+
wb_group = setup_test_group_1M(root, "per_memcg_wb_test1");
if (!wb_group)
return KSFT_FAIL;
- if (cg_write(wb_group, "memory.zswap.max", "10K"))
+ if (cg_write(wb_group, "memory.zswap.max", zswap_max_buf))
+ goto out;
+ if (cg_write(wb_group, "memory.max", mem_max_buf))
goto out;
+
control_group = setup_test_group_1M(root, "per_memcg_wb_test2");
if (!control_group)
goto out;
+ if (cg_write(control_group, "memory.max", mem_max_buf))
+ goto out;

/* Push some test_group2 memory into zswap */
if (cg_enter_current(control_group))
@@ -442,8 +451,8 @@ static int test_no_invasive_cgroup_shrink(const char *root)
if (cg_read_key_long(control_group, "memory.stat", "zswapped") < 1)
goto out;

- /* Allocate 10x memory.max to push wb_group memory into zswap and trigger wb */
- if (cg_run(wb_group, allocate_bytes, (void *)MB(10)))
+ /* Allocate 2x memory.max to push wb_group memory into zswap and trigger wb */
+ if (cg_run(wb_group, allocate_bytes, (void *)control_allocation_size))
goto out;

/* Verify that only zswapped memory from gwb_group has been written back */
--
2.53.0