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 <[email protected]> > Signed-off-by: Nhat Pham <[email protected]> > --- > 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.
