On Wed, May 8, 2024 at 3:22 AM Usama Arif <usamaarif642@xxxxxxxxx> wrote:
>
> Attempt writeback with the below steps and check using
> memory.stat.zswpwb if zswap writeback occurred:
> 1. Allocate memory.
> 2. Reclaim memory equal to the amount that was allocated in step 1.
> This will move it into zswap.
> 3. Save current zswap usage.
> 4. Move the memory allocated in step 1 back in from zswap.
> 5. Set zswap.max to half the amount that was recorded in step 3.
> 6. Attempt to reclaim memory equal to the amount that was allocated,
> this will either trigger writeback if it's enabled, or reclamation
> will fail if writeback is disabled as there isn't enough zswap
> space.
>
> Suggested-by: Nhat Pham <nphamcs@xxxxxxxxx>
> Signed-off-by: Usama Arif <usamaarif642@xxxxxxxxx>
> ---
>
> v3 -> v4 (Yosry Ahmed):
> - Use a fixed page-sized buffer for filling and checking memory when
> attempting writeback
> - Use cg_write_numeric instead of cg_write for memory.reclaim
> - Improved error checking for zswpwb_before and zswpwb_after
>
> v2 -> v3:
> - Remove memory.max (Yosry Ahmed)
> - change from random allocation of memory to increasing and 0 allocation
> (Yosry Ahmed)
> - stricter error checking when writeback is disabled (Yosry Ahmed)
> - Ensure zswpwb_before == 0 (Yosry Ahmed)
> - Variable definition reorder, function name change (Yosry Ahmed)
>
> v1 -> v2:
> - Change method of causing writeback from limit zswap to memory reclaim.
> (Further described in commit message) (Yosry Ahmed)
> - Document why using random memory (Nhat Pham)
> ---
> tools/testing/selftests/cgroup/test_zswap.c | 130 +++++++++++++++++++-
> 1 file changed, 129 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
> index f0e488ed90d8..beab9b979957 100644
> --- a/tools/testing/selftests/cgroup/test_zswap.c
> +++ b/tools/testing/selftests/cgroup/test_zswap.c
> @@ -50,7 +50,7 @@ static int get_zswap_stored_pages(size_t *value)
> return read_int("/sys/kernel/debug/zswap/stored_pages", value);
> }
>
> -static int get_cg_wb_count(const char *cg)
> +static long get_cg_wb_count(const char *cg)
> {
> return cg_read_key_long(cg, "memory.stat", "zswpwb");
> }
> @@ -248,6 +248,132 @@ static int test_zswapin(const char *root)
> return ret;
> }
>
> +/*
> + * Attempt writeback with the following steps:
> + * 1. Allocate memory.
> + * 2. Reclaim memory equal to the amount that was allocated in step 1.
> + This will move it into zswap.
> + * 3. Save current zswap usage.
> + * 4. Move the memory allocated in step 1 back in from zswap.
> + * 5. Set zswap.max to half the amount that was recorded in step 3.
> + * 6. Attempt to reclaim memory equal to the amount that was allocated,
> + this will either trigger writeback if it's enabled, or reclamation
> + will fail if writeback is disabled as there isn't enough zswap space.
> + */
> +static int attempt_writeback(const char *cgroup, void *arg)
> +{
> + long pagesize = sysconf(_SC_PAGESIZE);
> + char *test_group = arg;
> + size_t memsize = MB(4);
> + char buf[pagesize];
> + long zswap_usage;
> + bool wb_enabled;
> + int ret = -1;
> + char *mem;
> +
> + wb_enabled = cg_read_long(test_group, "memory.zswap.writeback");
> + mem = (char *)malloc(memsize);
> + if (!mem)
> + return ret;
> +
> + /*
> + * Fill half of each page with increasing data, and keep other
> + * half empty, this will result in data that is still compressible
> + * and ends up in zswap, with material zswap usage.
> + */
> + 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);
> +
> + /* Try and reclaim allocated memory */
> + if (cg_write_numeric(test_group, "memory.reclaim", memsize)) {
> + ksft_print_msg("Failed to reclaim all of the requested memory\n");
> + goto out;
> + }
> +
> + zswap_usage = cg_read_long(test_group, "memory.zswap.current");
> +
> + /* zswpin */
> + for (int i = 0; i < memsize; i += pagesize) {
> + if (memcmp(&mem[i], buf, pagesize)) {
> + ksft_print_msg("invalid memory\n");
> + goto out;
> + }
> + }
> +
> + if (cg_write_numeric(test_group, "memory.zswap.max", zswap_usage/2))
> + goto out;
> +
> + /*
> + * If writeback is enabled, trying to reclaim memory now will trigger a
> + * writeback as zswap.max is half of what was needed when reclaim ran the first time.
> + * If writeback is disabled, memory reclaim will fail as zswap is limited and
> + * it can't writeback to swap.
> + */
> + ret = cg_write(test_group, "memory.reclaim", "4M");
We need cg_write_numeric(.., memsize) here as well.
Otherwise, this LGTM. After fixing this, feel free to add:
Acked-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
> + if (!wb_enabled)
> + ret = (ret == -EAGAIN) ? 0 : -1;
> +
> +out:
> + free(mem);
> + return ret;
> +}
> +
> +/* Test to verify the zswap writeback path */
> +static int test_zswap_writeback(const char *root, bool wb)
> +{
> + long zswpwb_before, zswpwb_after;
> + int ret = KSFT_FAIL;
> + char *test_group;
> +
> + test_group = cg_name(root, "zswap_writeback_test");
> + if (!test_group)
> + goto out;
> + if (cg_create(test_group))
> + goto out;
> + if (cg_write(test_group, "memory.zswap.writeback", wb ? "1" : "0"))
> + goto out;
> +
> + zswpwb_before = get_cg_wb_count(test_group);
> + if (zswpwb_before != 0) {
> + ksft_print_msg("zswpwb_before = %ld instead of 0\n", zswpwb_before);
> + goto out;
> + }
> +
> + if (cg_run(test_group, attempt_writeback, (void *) test_group))
> + goto out;
> +
> + /* Verify that zswap writeback occurred only if writeback was enabled */
> + zswpwb_after = get_cg_wb_count(test_group);
> + if (zswpwb_after < 0)
> + goto out;
> +
> + if (wb != !!zswpwb_after) {
> + ksft_print_msg("zswpwb_after is %ld while wb is %s",
> + zswpwb_after, wb ? "enabled" : "disabled");
> + goto out;
> + }
> +
> + ret = KSFT_PASS;
> +
> +out:
> + cg_destroy(test_group);
> + free(test_group);
> + return ret;
> +}
> +
> +static int test_zswap_writeback_enabled(const char *root)
> +{
> + return test_zswap_writeback(root, true);
> +}
> +
> +static int test_zswap_writeback_disabled(const char *root)
> +{
> + return test_zswap_writeback(root, false);
> +}
> +
> /*
> * 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
> @@ -425,6 +551,8 @@ struct zswap_test {
> T(test_zswap_usage),
> T(test_swapin_nozswap),
> T(test_zswapin),
> + T(test_zswap_writeback_enabled),
> + T(test_zswap_writeback_disabled),
> T(test_no_kmem_bypass),
> T(test_no_invasive_cgroup_shrink),
> };
> --
> 2.43.0
>
