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selftests/cgroup: test_zswap: wait for asynchronous writeback

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zswap writeback is asynchronous, but test_zswap.c checks writeback
counters immediately after reclaim/trigger paths.  On some platforms (e.g.
ppc64le), this can race with background writeback and cause spurious
failures even when behavior is correct.

Add wait_for_writeback() to poll get_cg_wb_count() with a bounded
timeout, and use it in:

  test_zswap_writeback_one() when writeback is expected
  test_no_invasive_cgroup_shrink() for the wb_group check

This keeps the original before/after assertion style while making the
tests robust against writeback completion latency.

No test behavior change, selftest stability improvement only.

Link: https://lore.kernel.org/20260424040059.12940-9-li.wang@linux.dev
Signed-off-by: Li Wang <li.wang@linux.dev>
Acked-by: Nhat Pham <nphamcs@gmail.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: 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>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Jiayuan Chen <jiayuan.chen@linux.dev>
Cc: Waiman Long <longman@redhat.com>
Cc: Yosry Ahmed <yosry@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Li Wang 2026-04-24 12:00:59 +08:00 committed by Andrew Morton
parent 883015a9c3
commit e5ab892d05
1 changed files with 26 additions and 2 deletions
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28
tools/testing/selftests/cgroup/test_zswap.c
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@ -120,6 +120,27 @@ static char *setup_test_group_1M(const char *root, const char *name)
return NULL;
}
/*
* Writeback is asynchronous; poll until at least one writeback has
* been recorded for @cg, or until @timeout_ms has elapsed.
*/
static long wait_for_writeback(const char *cg, int timeout_ms)
{
long elapsed, count;
for (elapsed = 0; elapsed < timeout_ms; elapsed += 100) {
count = get_cg_wb_count(cg);
if (count < 0)
return -1;
if (count > 0)
return count;
usleep(100000);
}
return 0;
}
/*
* Sanity test to check that pages are written into zswap.
*/
@ -345,7 +366,10 @@ static int test_zswap_writeback_one(const char *cgroup, bool wb)
return -1;
/* Verify that zswap writeback occurred only if writeback was enabled */
zswpwb_after = get_cg_wb_count(cgroup);
if (wb)
zswpwb_after = wait_for_writeback(cgroup, 5000);
else
zswpwb_after = get_cg_wb_count(cgroup);
if (zswpwb_after < 0)
return -1;
@ -476,7 +500,7 @@ static int test_no_invasive_cgroup_shrink(const char *root)
}
/* Verify that only zswapped memory from gwb_group has been written back */
if (get_cg_wb_count(wb_group) > 0 && get_cg_wb_count(zw_group) == 0)
if (wait_for_writeback(wb_group, 5000) > 0 && get_cg_wb_count(zw_group) == 0)
ret = KSFT_PASS;
out:
cg_enter_current(root);