Re: [PATCH v1 5/5] kselftests: cgroup: add perpcu memory accounting test

Dennis Zhou
2020-06-05T20:07:56Z

On Thu, May 28, 2020 at 04:25:08PM -0700, Roman Gushchin wrote:
> Add a simple test to check the percpu memory accounting.
> The test creates a cgroup tree with 1000 child cgroups
> and checks values of memory.current and memory.stat::percpu.
>
> Signed-off-by: Roman Gushchin <guro@fb.com>
> ---
> tools/testing/selftests/cgroup/test_kmem.c | 59 ++++++++++++++++++++++
> 1 file changed, 59 insertions(+)
>
> diff --git a/tools/testing/selftests/cgroup/test_kmem.c b/tools/testing/selftests/cgroup/test_kmem.c
> index 5224dae216e5..a0d4f1a3137d 100644
> --- a/tools/testing/selftests/cgroup/test_kmem.c
> +++ b/tools/testing/selftests/cgroup/test_kmem.c
> @@ -331,6 +331,64 @@ static int test_kmem_dead_cgroups(const char *root)
> return ret;
> }
>
> +/*
> + * This test creates a sub-tree with 1000 memory cgroups.
> + * Then it checks that the memory.current on the parent level
> + * is greater than 0 and approximates matches the percpu value
> + * from memory.stat.
> + */
> +static int test_percpu_basic(const char *root)
> +{
> + int ret = KSFT_FAIL;
> + char *parent, *child;
> + long current, percpu;
> + int i;
> +
> + parent = cg_name(root, "percpu_basic_test");
> + if (!parent)
> + goto cleanup;
> +
> + if (cg_create(parent))
> + goto cleanup;
> +
> + if (cg_write(parent, "cgroup.subtree_control", "+memory"))
> + goto cleanup;
> +
> + for (i = 0; i < 1000; i++) {
> + child = cg_name_indexed(parent, "child", i);
> + if (!child)
> + return -1;
> +
> + if (cg_create(child))
> + goto cleanup_children;
> +
> + free(child);
> + }
> +
> + current = cg_read_long(parent, "memory.current");
> + percpu = cg_read_key_long(parent, "memory.stat", "percpu ");
> +
> + if (current > 0 && percpu > 0 && abs(current - percpu) <
> + 4096 * 32 * get_nprocs())

So this is checking that we've allocated less than 32 pages per cpu over
1000 child cgroups that's not percpu memory? Is there a more definitive
measurement or at least a comment we can leave saying why this limit was
chosen.

> + ret = KSFT_PASS;
> + else
> + printf("memory.current %ld\npercpu %ld\n",
> + current, percpu);
> +
> +cleanup_children:
> + for (i = 0; i < 1000; i++) {
> + child = cg_name_indexed(parent, "child", i);
> + cg_destroy(child);
> + free(child);
> + }
> +
> +cleanup:
> + cg_destroy(parent);
> + free(parent);
> +
> + return ret;
> +}
> +
> #define T(x) { x, #x }
> struct kmem_test {
> int (*fn)(const char *root);
> @@ -341,6 +399,7 @@ struct kmem_test {
> T(test_kmem_proc_kpagecgroup),
> T(test_kmem_kernel_stacks),
> T(test_kmem_dead_cgroups),
> + T(test_percpu_basic),
> };
> #undef T
>
> --
> 2.25.4
>
>