On Mon, Jan 29, 2024 at 02:45:42PM -0800, Nhat Pham wrote:
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
s/memories/memory
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++) {
What benefit does the iteration serve here? I would guess one iteration is enough to swap everything in at least once, no?
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);
}
I don't like how we reuse allocate_bytes_and_read(), we are not saving much. Let's keep allocate_bytes() as-is and add a separate helper. Also, I think allocate_and_read_bytes() is easier to read.
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");
+}
Why are we testing the no zswap case? I am all for testing but it seems out of scope here. It would have been understandable if we are testing memory.zswap.max itself, but we are not doing that.
FWIW, I think the tests here should really be separated from cgroup tests, but I understand why they were added here. There is a lot of testing for memcg interface and control for zswap, and a lot of nice helpers present.