The patch titled Subject: selftests: add a sanity check for zswap has been added to the -mm mm-unstable branch. Its filename is selftests-add-a-sanity-check-for-zswap.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-add-a-sanity-check-for-zswap.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Nhat Pham <nphamcs@xxxxxxxxx> Subject: selftests: add a sanity check for zswap Date: Fri, 20 Oct 2023 15:20:09 -0700 We recently encountered a bug that makes all zswap store attempt fail. Specifically, after: "141fdeececb3 mm/zswap: delay the initialization of zswap" if we build a kernel with zswap disabled by default, then enabled after the swapfile is set up, the zswap tree will not be initialized. As a result, all zswap store calls will be short-circuited. We have to perform another swapon to get zswap working properly again. Fortunately, this issue has since been fixed by the patch that kills frontswap: "42c06a0e8ebe mm: kill frontswap" which performs zswap_swapon() unconditionally, i.e always initializing the zswap tree. This test add a sanity check that ensure zswap storing works as intended. Link: https://lkml.kernel.org/r/20231020222009.2358953-1-nphamcs@xxxxxxxxx Signed-off-by: Nhat Pham <nphamcs@xxxxxxxxx> Acked-by: Rik van Riel <riel@xxxxxxxxxxx> Cc: Domenico Cerasuolo <cerasuolodomenico@xxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Shuah Khan <shuah@xxxxxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Cc: Zefan Li <lizefan.x@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- tools/testing/selftests/cgroup/test_zswap.c | 48 ++++++++++++++++++ 1 file changed, 48 insertions(+) --- a/tools/testing/selftests/cgroup/test_zswap.c~selftests-add-a-sanity-check-for-zswap +++ a/tools/testing/selftests/cgroup/test_zswap.c @@ -55,6 +55,11 @@ static int get_zswap_written_back_pages( return read_int("/sys/kernel/debug/zswap/written_back_pages", value); } +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) { size_t size = (size_t)arg; @@ -69,6 +74,48 @@ static int allocate_bytes(const char *cg } /* + * Sanity test to check that pages are written into zswap. + */ +static int test_zswap_usage(const char *root) +{ + long zswpout_before, zswpout_after; + int ret = KSFT_FAIL; + char *test_group; + + /* Set up */ + test_group = cg_name(root, "no_shrink_test"); + if (!test_group) + goto out; + if (cg_create(test_group)) + goto out; + if (cg_write(test_group, "memory.max", "1M")) + goto out; + + zswpout_before = get_zswpout(test_group); + if (zswpout_before < 0) { + ksft_print_msg("Failed to get zswpout\n"); + goto out; + } + + /* Allocate more than memory.max to push memory into zswap */ + if (cg_run(test_group, allocate_bytes, (void *)MB(4))) + goto out; + + /* Verify that pages come into zswap */ + zswpout_after = get_zswpout(test_group); + if (zswpout_after <= zswpout_before) { + ksft_print_msg("zswpout does not increase after test program\n"); + goto out; + } + 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 not be triggered. * @@ -235,6 +282,7 @@ struct zswap_test { int (*fn)(const char *root); const char *name; } tests[] = { + T(test_zswap_usage), T(test_no_kmem_bypass), T(test_no_invasive_cgroup_shrink), }; _ Patches currently in -mm which might be from nphamcs@xxxxxxxxx are zswap-export-compression-failure-stats.patch selftests-add-a-sanity-check-for-zswap.patch