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

[Dennis Zhou <dennis@kernel.org>]

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
> 
>