selftests: cgroup: add test_zswap program

Patch series "selftests: cgroup: add zswap test program".

This series adds 2 zswap related selftests that verify known and fixed
issues.  A new dedicated test program (test_zswap) is proposed since the
test cases are specific to zswap and hosts specific helpers.

The first patch adds the (empty) test program, while the other 2 add an
actual test function each.


This patch (of 3):

Add empty cgroup-zswap self test scaffold program, test functions to be
added in the next commits.

Link: https://lkml.kernel.org/r/20230621153548.428093-1-cerasuolodomenico@gmail.com
Link: https://lkml.kernel.org/r/20230621153548.428093-2-cerasuolodomenico@gmail.com


Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Cc: Zefan Li <lizefan.x@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>