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Wed, 17 Jun 2026 21:50:04 -0700 (PDT) From: Hao Jia To: akpm@linux-foundation.org, tj@kernel.org, hannes@cmpxchg.org, shakeel.butt@linux.dev, mhocko@kernel.org, yosry@kernel.org, mkoutny@suse.com, nphamcs@gmail.com, chengming.zhou@linux.dev, muchun.song@linux.dev, roman.gushchin@linux.dev Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Hao Jia Subject: [PATCH v4 5/5] selftests/cgroup: Add tests for zswap proactive writeback Date: Thu, 18 Jun 2026 12:48:57 +0800 Message-Id: <20260618044857.69439-6-jiahao.kernel@gmail.com> X-Mailer: git-send-email 2.39.2 (Apple Git-143) In-Reply-To: <20260618044857.69439-1-jiahao.kernel@gmail.com> References: <20260618044857.69439-1-jiahao.kernel@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Hao Jia Add test_zswap_proactive_writeback() to cover the new memory.reclaim "zswap_writeback_only" key. The test populates a memory cgroup zswap pool, triggers proactive writeback, and verifies the behavior by observing the change in zswpwb_proactive_b. Invalid input combinations are also covered. Extend test_zswap_writeback_one() to assert that the existing non-proactive writeback path leaves zswpwb_proactive_b at zero. Signed-off-by: Hao Jia --- tools/testing/selftests/cgroup/test_zswap.c | 153 +++++++++++++++++++- 1 file changed, 152 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c index 49b36ee79160..9c153fdd3a08 100644 --- a/tools/testing/selftests/cgroup/test_zswap.c +++ b/tools/testing/selftests/cgroup/test_zswap.c @@ -60,7 +60,12 @@ static int get_zswap_stored_pages(size_t *value) static long get_cg_wb_count(const char *cg) { - return cg_read_key_long(cg, "memory.stat", "zswpwb"); + return cg_read_key_long(cg, "memory.stat", "zswpwb "); +} + +static long get_cg_pwb_bytes(const char *cg) +{ + return cg_read_key_long(cg, "memory.stat", "zswpwb_proactive_b "); } static long get_zswpout(const char *cgroup) @@ -355,6 +360,7 @@ static int attempt_writeback(const char *cgroup, void *arg) static int test_zswap_writeback_one(const char *cgroup, bool wb) { long zswpwb_before, zswpwb_after; + long pwb_bytes; zswpwb_before = get_cg_wb_count(cgroup); if (zswpwb_before != 0) { @@ -362,6 +368,12 @@ static int test_zswap_writeback_one(const char *cgroup, bool wb) return -1; } + pwb_bytes = get_cg_pwb_bytes(cgroup); + if (pwb_bytes != 0) { + ksft_print_msg("zswpwb_proactive_b_before = %ld instead of 0\n", pwb_bytes); + return -1; + } + if (cg_run(cgroup, attempt_writeback, (void *) &wb)) return -1; @@ -379,6 +391,17 @@ static int test_zswap_writeback_one(const char *cgroup, bool wb) return -1; } + /* + * attempt_writeback() does not use the proactive writeback path, so + * zswpwb_proactive_b must stay at zero regardless of whether + * writeback was enabled. + */ + pwb_bytes = get_cg_pwb_bytes(cgroup); + if (pwb_bytes != 0) { + ksft_print_msg("zswpwb_proactive_b_after is %ld, expected 0\n", pwb_bytes); + return -1; + } + return 0; } @@ -770,6 +793,133 @@ static int test_zswap_incompressible(const char *root) return ret; } +/* + * Trigger proactive zswap writeback with the following steps: + * 1. Allocate memory. + * 2. Push allocated memory into zswap. + * 3. Proactively write back zswap pages to swap + * using "zswap_writeback_only". + */ +static int proactive_writeback_workload(const char *cgroup, void *arg) +{ + long pagesize = sysconf(_SC_PAGESIZE); + size_t memsize = pagesize * 1024; + char reclaim_cmd[64]; + char buf[pagesize]; + long zswap_usage; + int ret = -1; + int rc; + char *mem; + + mem = (char *)malloc(memsize); + if (!mem) + return ret; + + for (int i = 0; i < pagesize; i++) + buf[i] = i < pagesize / 2 ? (char)i : 0; + for (int i = 0; i < memsize; i += pagesize) + memcpy(&mem[i], buf, pagesize); + + /* Evict allocated memory into zswap. */ + if (cg_write_numeric(cgroup, "memory.reclaim", memsize)) { + ksft_print_msg("Failed to push pages into zswap\n"); + goto out; + } + + zswap_usage = cg_read_long(cgroup, "memory.zswap.current"); + if (zswap_usage <= 0) { + ksft_print_msg("no zswap pool to write back\n"); + goto out; + } + + /* Trigger proactive zswap writeback. */ + snprintf(reclaim_cmd, sizeof(reclaim_cmd), "%zu zswap_writeback_only", zswap_usage); + rc = cg_write(cgroup, "memory.reclaim", reclaim_cmd); + if (rc && rc != -EAGAIN) { + ksft_print_msg("proactive zswap writeback failed: %d\n", rc); + goto out; + } + + ret = 0; +out: + free(mem); + return ret; +} + +static int check_writeback_invalid_inputs(const char *cgroup) +{ + static char * const bad_inputs[] = { + "zswap_writeback_only", + "1M zswap_writeback_only swappiness=60", + "1M swappiness=60 zswap_writeback_only", + "1M zswap_writeback_only swappiness=max", + "1M swappiness=max zswap_writeback_only", + }; + int i, rc; + + for (i = 0; i < ARRAY_SIZE(bad_inputs); i++) { + rc = cg_write(cgroup, "memory.reclaim", bad_inputs[i]); + if (rc != -EINVAL) { + ksft_print_msg("memory.reclaim '%s': returned %d, expected %d\n", + bad_inputs[i], rc, -EINVAL); + return -1; + } + } + return 0; +} + +static int test_zswap_proactive_writeback(const char *root) +{ + long wb_before, wb_after; + long pwb_b_before, pwb_b_after; + long wb_delta, pwb_b_delta; + int ret = KSFT_FAIL; + char *test_group; + + if (cg_read_strcmp(root, "memory.zswap.writeback", "1")) + return KSFT_SKIP; + + test_group = cg_name(root, "zswap_proactive_test"); + if (!test_group) + return KSFT_FAIL; + if (cg_create(test_group)) + goto out; + if (check_writeback_invalid_inputs(test_group)) + goto out; + + pwb_b_before = get_cg_pwb_bytes(test_group); + wb_before = get_cg_wb_count(test_group); + if (pwb_b_before < 0 || wb_before < 0) + goto out; + + if (cg_run(test_group, proactive_writeback_workload, NULL)) + goto out; + + pwb_b_after = get_cg_pwb_bytes(test_group); + wb_after = get_cg_wb_count(test_group); + if (pwb_b_after < 0 || wb_after < 0) + goto out; + + pwb_b_delta = pwb_b_after - pwb_b_before; + wb_delta = wb_after - wb_before; + + if (pwb_b_delta <= 0) { + ksft_print_msg("zswpwb_proactive_b did not increase: delta=%ld\n", + pwb_b_delta); + goto out; + } + if (wb_delta <= 0) { + ksft_print_msg("zswpwb did not increase: delta=%ld\n", wb_delta); + goto out; + } + + ret = KSFT_PASS; +out: + cg_destroy(test_group); + free(test_group); + return ret; +} + #define T(x) { x, #x } struct zswap_test { int (*fn)(const char *root); @@ -783,6 +933,7 @@ struct zswap_test { T(test_no_kmem_bypass), T(test_no_invasive_cgroup_shrink), T(test_zswap_incompressible), + T(test_zswap_proactive_writeback), }; #undef T -- 2.34.1