Re: [PATCH v4 4/4] selftests: cgroup: add a selftest for memory.reclaim

[Shakeel Butt]

On Thu, Apr 21, 2022 at 11:44:26PM +0000, Yosry Ahmed wrote:
> Add a new test for memory.reclaim that verifies that the interface
> correctly reclaims memory as intended, from both anon and file pages.
> 
> Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
> Acked-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>
> ---
>  .../selftests/cgroup/test_memcontrol.c        | 86 +++++++++++++++++++
>  1 file changed, 86 insertions(+)
> 
> diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c b/tools/testing/selftests/cgroup/test_memcontrol.c
> index f2ffb3a30194..5f7c20de2426 100644
> --- a/tools/testing/selftests/cgroup/test_memcontrol.c
> +++ b/tools/testing/selftests/cgroup/test_memcontrol.c
> @@ -760,6 +760,91 @@ static int test_memcg_max(const char *root)
>  	return ret;
>  }
>  
> +/*
> + * This test checks that memory.reclaim reclaims the given
> + * amount of memory (from both anon and file).
> + */
> +static int test_memcg_reclaim(const char *root)
> +{
> +	int ret = KSFT_FAIL, fd, retries;
> +	char *memcg;
> +	long current, to_reclaim;
> +	char buf[64];
> +
> +	memcg = cg_name(root, "memcg_test");
> +	if (!memcg)
> +		goto cleanup;
> +
> +	if (cg_create(memcg))
> +		goto cleanup;
> +
> +	current = cg_read_long(memcg, "memory.current");
> +	if (current != 0)
> +		goto cleanup;
> +
> +	cg_run_nowait(memcg, alloc_anon_noexit, (void *) MB(50));

Don't you need is_swap_enabled() check before deciding to do the anon
allocations?

> +	sleep(1);
> +
> +	fd = get_temp_fd();
> +	if (fd < 0)
> +		goto cleanup;
> +
> +	cg_run_nowait(memcg, alloc_pagecache_50M_noexit, (void *)(long)fd);
> +	sleep(1);

These sleep(1)s do not seem robust. Since kernel keeps the page cache
around, you can convert anon to use tmpfs and use simple cg_run to
trigger the allocations of anon (tmpfs) and file which will remain in
memory even after return from cg_run.