[PATCH 3/3] selftests: add test for zswapin

Nhat Pham
2024-01-29T22:45:46Z

We recently encountered a kernel crash on the zswapin path in our
internal kernel, which went undetected because of a lack of test
coverage for this path. Add a selftest to cover this code path,
allocating more memories than the cgroup limit to trigger
swapout/zswapout, then reading the pages back in memories several times.

Also add a variant of this test that runs with zswap disabled, to verify
swapin correctness as well.

Suggested-by: Rik van Riel <riel@surriel.com>
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
---
tools/testing/selftests/cgroup/test_zswap.c | 67 ++++++++++++++++++++-
1 file changed, 65 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
index 32ce975b21d1..86231c86dc89 100644
--- a/tools/testing/selftests/cgroup/test_zswap.c
+++ b/tools/testing/selftests/cgroup/test_zswap.c
@@ -60,17 +60,39 @@ static long get_zswpout(const char *cgroup)
return cg_read_key_long(cgroup, "memory.stat", "zswpout ");
}

-static int allocate_bytes(const char *cgroup, void *arg)
+static int allocate_bytes_and_read(const char *cgroup, void *arg, bool read)
{
size_t size = (size_t)arg;
char *mem = (char *)malloc(size);
+ int ret = 0;

if (!mem)
return -1;
for (int i = 0; i < size; i += 4095)
mem[i] = 'a';
+
+ if (read) {
+ /* cycle through the allocated memory to (z)swap in and out pages */
+ for (int t = 0; t < 5; t++) {
+ for (int i = 0; i < size; i += 4095) {
+ if (mem[i] != 'a')
+ ret = -1;
+ }
+ }
+ }
+
free(mem);
- return 0;
+ return ret;
+}
+
+static int allocate_bytes(const char *cgroup, void *arg)
+{
+ return allocate_bytes_and_read(cgroup, arg, false);
+}
+
+static int read_bytes(const char *cgroup, void *arg)
+{
+ return allocate_bytes_and_read(cgroup, arg, true);
}

static char *setup_test_group_1M(const char *root, const char *name)
@@ -133,6 +155,45 @@ static int test_zswap_usage(const char *root)
return ret;
}

+/* Simple test to verify the (z)swapin code paths */
+static int test_zswapin_size(const char *root, char *zswap_size)
+{
+ int ret = KSFT_FAIL;
+ char *test_group;
+
+ /* Set up */
+ test_group = cg_name(root, "zswapin_test");
+ if (!test_group)
+ goto out;
+ if (cg_create(test_group))
+ goto out;
+ if (cg_write(test_group, "memory.max", "8M"))
+ goto out;
+ if (cg_write(test_group, "memory.zswap.max", zswap_size))
+ goto out;
+
+ /* Allocate and read more than memory.max to trigger (z)swap in */
+ if (cg_run(test_group, read_bytes, (void *)MB(32)))
+ goto out;
+
+ ret = KSFT_PASS;
+
+out:
+ cg_destroy(test_group);
+ free(test_group);
+ return ret;
+}
+
+static int test_swapin(const char *root)
+{
+ return test_zswapin_size(root, "0");
+}
+
+static int test_zswapin_no_limit(const char *root)
+{
+ return test_zswapin_size(root, "max");
+}
+
/*
* When trying to store a memcg page in zswap, if the memcg hits its memory
* limit in zswap, writeback should affect only the zswapped pages of that
@@ -309,6 +370,8 @@ struct zswap_test {
const char *name;
} tests[] = {
T(test_zswap_usage),
+ T(test_swapin),
+ T(test_zswapin_no_limit),
T(test_no_kmem_bypass),
T(test_no_invasive_cgroup_shrink),
};
--
2.39.3