Hey Nhat, I have a few more comments, sorry for not catching everything the first time around.
Adding Roman to CC. On Wed, Jan 31, 2024 at 07:27:18PM -0800, Nhat Pham wrote: > Add a selftest to cover the zswapin code path, allocating more memory > than the cgroup limit to trigger swapout/zswapout, then reading the > pages back in memory several times. This is inspired by a recently > encountered 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 verify that when memory.zswap.max = 0, no pages can go > to the zswap pool for the cgroup. > > Suggested-by: Rik van Riel <[email protected]> > Suggested-by: Yosry Ahmed <[email protected]> > Signed-off-by: Nhat Pham <[email protected]> > --- > tools/testing/selftests/cgroup/test_zswap.c | 97 +++++++++++++++++++++ > 1 file changed, 97 insertions(+) > > diff --git a/tools/testing/selftests/cgroup/test_zswap.c > b/tools/testing/selftests/cgroup/test_zswap.c > index 32ce975b21d1..14d1f18f1098 100644 > --- a/tools/testing/selftests/cgroup/test_zswap.c > +++ b/tools/testing/selftests/cgroup/test_zswap.c > @@ -60,6 +60,27 @@ static long get_zswpout(const char *cgroup) > return cg_read_key_long(cgroup, "memory.stat", "zswpout "); > } > > +static int allocate_bytes_and_read(const char *cgroup, void *arg) I think allocate_and_read_bytes() is easier to read, but I don't feel strongly about it. > +{ > + 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'; cgroup_util.h defines PAGE_SIZE, see alloc_anon() for example. On that note, alloc_anon() is awfully close to allocate_bytes() below, perhaps we should consolidate them. The only difference I see is that alloc_anon() does not check for the allocation failure, but a lot of functions in cgroup_helpers.c don't, so it seems intentional for simplification. > + > + /* go through the allocated memory to (z)swap in and out pages */ > + for (int i = 0; i < size; i += 4095) { > + if (mem[i] != 'a') > + ret = -1; > + } > + > + free(mem); > + return ret; > +} > + > static int allocate_bytes(const char *cgroup, void *arg) > { > size_t size = (size_t)arg; > @@ -133,6 +154,80 @@ static int test_zswap_usage(const char *root) > return ret; > } > > +/* > + * Check that when memory.zswap.max = 0, no pages can go to the zswap pool > for > + * the cgroup. > + */ > +static int test_swapin_nozswap(const char *root) > +{ > + int ret = KSFT_FAIL; > + char *test_group; > + long zswpout; > + > + /* Set up */ I think this comment is unnecessary. > + test_group = cg_name(root, "no_zswap_test"); > + > + if (!test_group) > + goto out; > + if (cg_create(test_group)) > + goto out; > + if (cg_write(test_group, "memory.max", "8M")) > + goto out; > + /* Disable zswap */ I think this comment is unnecessary. > + if (cg_write(test_group, "memory.zswap.max", "0")) > + goto out; > + > + /* Allocate and read more than memory.max to trigger swapin */ > + if (cg_run(test_group, allocate_bytes_and_read, (void *)MB(32))) > + goto out; > + > + /* Verify that no zswap happened */ If we want to be really meticulous, we can verify that we did swap out, but not to zswap. IOW, we can check memory.swap.current or something. > + zswpout = get_zswpout(test_group); > + if (zswpout < 0) { > + ksft_print_msg("Failed to get zswpout\n"); > + goto out; > + } else if (zswpout > 0) { nit: This can be a separate if condition, I think it would be more inline with the style of separate consecutive if blocks we are following. > + ksft_print_msg( > + "Pages should not go to zswap when memory.zswap.max = > 0\n"); We can probably avoid the line break with something more concise, for example: "zswapout > 0 when zswap is disabled" or "zswapout > 0 when memory.zswap.max = 0" > + goto out; > + } > + ret = KSFT_PASS; > + > +out: > + cg_destroy(test_group); > + free(test_group); > + return ret; > +} > + > +/* Simple test to verify the (z)swapin code paths */ > +static int test_zswapin_no_limit(const char *root) I think test_zswapin() is enough to be distinct from test_swapin_nozswap(). The limit is not a factor here AFAICT. > +{ > + int ret = KSFT_FAIL; > + char *test_group; > + > + /* Set up */ I think this comment is unnecessary. > + 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", "max")) > + goto out; > + > + /* Allocate and read more than memory.max to trigger (z)swap in */ > + if (cg_run(test_group, allocate_bytes_and_read, (void *)MB(32))) > + goto out; We should probably check for a positive zswapin here, no? > + > + ret = KSFT_PASS; > + > +out: > + cg_destroy(test_group); > + free(test_group); > + return ret; > +} > + > /* > * 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 +404,8 @@ struct zswap_test { > const char *name; > } tests[] = { > T(test_zswap_usage), > + T(test_swapin_nozswap), > + T(test_zswapin_no_limit), > T(test_no_kmem_bypass), > T(test_no_invasive_cgroup_shrink), > }; > -- > 2.39.3
