From: Li Wang <li.wang@linux.dev>
To: akpm@linux-foundation.org, tj@kernel.org, longman@redhat.com,
roman.gushchin@linux.dev, hannes@cmpxchg.org, yosry@kernel.org,
jiayuan.chen@linux.dev, nphamcs@gmail.com,
chengming.zhou@linux.dev, mkoutny@suse.com, shuah@kernel.org
Cc: linux-mm@kvack.org, cgroups@vger.kernel.org,
linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
Michal Hocko <mhocko@kernel.org>,
Muchun Song <muchun.song@linux.dev>,
Shakeel Butt <shakeel.butt@linux.dev>,
Yosry Ahmed <yosryahmed@google.com>
Subject: [PATCH v7 8/8] selftests/cgroup: test_zswap: wait for asynchronous writeback
Date: Fri, 24 Apr 2026 12:00:59 +0800 [thread overview]
Message-ID: <20260424040059.12940-9-li.wang@linux.dev> (raw)
In-Reply-To: <20260424040059.12940-1-li.wang@linux.dev>
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.
Signed-off-by: Li Wang <li.wang@linux.dev>
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>
Acked-by: Nhat Pham <nphamcs@gmail.com>
---
tools/testing/selftests/cgroup/test_zswap.c | 28 +++++++++++++++++++--
1 file changed, 26 insertions(+), 2 deletions(-)
diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
index 5fe0cffb557..49b36ee7916 100644
--- a/tools/testing/selftests/cgroup/test_zswap.c
+++ b/tools/testing/selftests/cgroup/test_zswap.c
@@ -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);
--
2.53.0
next prev parent reply other threads:[~2026-04-24 4:02 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-24 4:00 [PATCH v7 0/8] selftests/cgroup: improve zswap tests robustness and support large page sizes Li Wang
2026-04-24 4:00 ` [PATCH v7 1/8] selftests/cgroup: skip test_zswap if zswap is globally disabled Li Wang
2026-04-24 4:00 ` [PATCH v7 2/8] selftests/cgroup: avoid OOM in test_swapin_nozswap Li Wang
2026-04-24 4:00 ` [PATCH v7 3/8] selftests/cgroup: use runtime page size for zswpin check Li Wang
2026-04-24 4:00 ` [PATCH v7 4/8] selftests/cgroup: rename PAGE_SIZE to BUF_SIZE in cgroup_util Li Wang
[not found] ` <20260424051557.8AA6AC19425@smtp.kernel.org>
2026-04-24 6:04 ` Li Wang
2026-04-24 4:00 ` [PATCH v7 5/8] selftests/cgroup: replace hardcoded page size values in test_zswap Li Wang
2026-04-24 5:20 ` Jiayuan Chen
2026-04-24 4:00 ` [PATCH v7 6/8] selftest/cgroup: fix zswap test_no_invasive_cgroup_shrink on large pagesize system Li Wang
2026-04-24 4:00 ` [PATCH v7 7/8] selftest/cgroup: fix zswap attempt_writeback() on 64K " Li Wang
2026-04-24 4:00 ` Li Wang [this message]
2026-04-24 10:06 ` [PATCH v7 0/8] selftests/cgroup: improve zswap tests robustness and support large page sizes Andrew Morton
2026-04-24 11:14 ` Li Wang
2026-04-24 13:31 ` Andrew Morton
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