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    Subject[PATCH v3 4/5] selftests: cgroup: update per-memcg zswap writeback selftest
    Date
    From: Domenico Cerasuolo <cerasuolodomenico@gmail.com>

    The memcg-zswap self test is updated to adjust to the behavior change
    implemented by commit 87730b165089 ("zswap: make shrinking memcg-aware"),
    where zswap performs writeback for specific memcg.

    Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
    Signed-off-by: Nhat Pham <nphamcs@gmail.com>
    ---
    tools/testing/selftests/cgroup/test_zswap.c | 74 ++++++++++++++-------
    1 file changed, 50 insertions(+), 24 deletions(-)

    diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
    index 49def87a909b..11271fabeffc 100644
    --- a/tools/testing/selftests/cgroup/test_zswap.c
    +++ b/tools/testing/selftests/cgroup/test_zswap.c
    @@ -50,9 +50,9 @@ static int get_zswap_stored_pages(size_t *value)
    return read_int("/sys/kernel/debug/zswap/stored_pages", value);
    }

    -static int get_zswap_written_back_pages(size_t *value)
    +static int get_cg_wb_count(const char *cg)
    {
    - return read_int("/sys/kernel/debug/zswap/written_back_pages", value);
    + return cg_read_key_long(cg, "memory.stat", "zswap_wb");
    }

    static int allocate_bytes(const char *cgroup, void *arg)
    @@ -68,45 +68,71 @@ static int allocate_bytes(const char *cgroup, void *arg)
    return 0;
    }

    +static char *setup_test_group_1M(const char *root, const char *name)
    +{
    + char *group_name = cg_name(root, name);
    +
    + if (!group_name)
    + return NULL;
    + if (cg_create(group_name))
    + goto fail;
    + if (cg_write(group_name, "memory.max", "1M")) {
    + cg_destroy(group_name);
    + goto fail;
    + }
    + return group_name;
    +fail:
    + free(group_name);
    + return NULL;
    +}
    +
    /*
    * When trying to store a memcg page in zswap, if the memcg hits its memory
    - * limit in zswap, writeback should not be triggered.
    - *
    - * This was fixed with commit 0bdf0efa180a("zswap: do not shrink if cgroup may
    - * not zswap"). Needs to be revised when a per memcg writeback mechanism is
    - * implemented.
    + * limit in zswap, writeback should affect only the zswapped pages of that
    + * memcg.
    */
    static int test_no_invasive_cgroup_shrink(const char *root)
    {
    - size_t written_back_before, written_back_after;
    int ret = KSFT_FAIL;
    - char *test_group;
    + size_t control_allocation_size = MB(10);
    + char *control_allocation, *wb_group = NULL, *control_group = NULL;

    /* Set up */
    - test_group = cg_name(root, "no_shrink_test");
    - if (!test_group)
    - goto out;
    - if (cg_create(test_group))
    + wb_group = setup_test_group_1M(root, "per_memcg_wb_test1");
    + if (!wb_group)
    + return KSFT_FAIL;
    + if (cg_write(wb_group, "memory.zswap.max", "10K"))
    goto out;
    - if (cg_write(test_group, "memory.max", "1M"))
    + control_group = setup_test_group_1M(root, "per_memcg_wb_test2");
    + if (!control_group)
    goto out;
    - if (cg_write(test_group, "memory.zswap.max", "10K"))
    +
    + /* Push some test_group2 memory into zswap */
    + if (cg_enter_current(control_group))
    goto out;
    - if (get_zswap_written_back_pages(&written_back_before))
    + control_allocation = malloc(control_allocation_size);
    + for (int i = 0; i < control_allocation_size; i += 4095)
    + control_allocation[i] = 'a';
    + if (cg_read_key_long(control_group, "memory.stat", "zswapped") < 1)
    goto out;

    - /* Allocate 10x memory.max to push memory into zswap */
    - if (cg_run(test_group, allocate_bytes, (void *)MB(10)))
    + /* Allocate 10x memory.max to push wb_group memory into zswap and trigger wb */
    + if (cg_run(wb_group, allocate_bytes, (void *)MB(10)))
    goto out;

    - /* Verify that no writeback happened because of the memcg allocation */
    - if (get_zswap_written_back_pages(&written_back_after))
    - goto out;
    - if (written_back_after == written_back_before)
    + /* Verify that only zswapped memory from gwb_group has been written back */
    + if (get_cg_wb_count(wb_group) > 0 && get_cg_wb_count(control_group) == 0)
    ret = KSFT_PASS;
    out:
    - cg_destroy(test_group);
    - free(test_group);
    + cg_enter_current(root);
    + if (control_group) {
    + cg_destroy(control_group);
    + free(control_group);
    + }
    + cg_destroy(wb_group);
    + free(wb_group);
    + if (control_allocation)
    + free(control_allocation);
    return ret;
    }

    --
    2.34.1
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