Re: [PATCH v2 2/4] selftests/cgroup: add memcg_stat_cross_cpu correctness test for flush

[Ziyang Men <ziyang.meme@gmail.com>]

On Wed, Jul 22, 2026 at 11:42:58AM -0700, JP Kobryn wrote:
>On 7/21/26 10:48 AM, Ziyang Men wrote:
>>Add a test_progs selftest that verifies the memory-cgroup BPF kfuncs
>>return values that agree with what userspace reads from cgroupfs, across
>>a whole cgroup subtree that has been charged on many CPUs.
>>
>>It complements the existing cgroup_iter_memcg test.  cgroup_iter_memcg
>>calls the memcg kfuncs on a single cgroup (BPF_CGROUP_ITER_SELF_ONLY) and
>>only asserts each value is greater than zero, so it never checks that a
>>value is actually correct.  This test compares the kfunc values against
>>what userspace reads from memory.stat, and checks every node in the
>>cgroup tree.
>>
>Can you extend the existing test instead of adding a new one?

Hi JP,

Good suggestion. Actually extending the exisiting one was the plan in the v1.
However, existing selftests with similar purpose is the cgroup_iter_memcg, which
is in the bpf/. After discussed with the bpf reviewer in v1, we think this
selftest may suit better in the cgroup/ rather than the bpf/, since 1) it tests
the cgroup functionalities (bpf is a tool), and 2) together with the selftest,
this patch serials also ships a common Makefile lib.bpf.mk for easily compiling
selftests for other subsystems using bpf. Currently there is no other selftests
in cgroup/ relies on BPF and we think it is good to put this selftest here as
the first consumer.

We appreciate any possible suggestions. Thanks very much!

Best,
Ziyang