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From:   Hao Luo <haoluo@google.com>
Date:   Mon, 18 Jul 2022 17:19:30 -0700
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Subject: Re: [PATCH bpf-next v3 8/8] bpf: add a selftest for cgroup
 hierarchical stats collection
To:     Yosry Ahmed <yosryahmed@google.com>
Cc:     Yonghong Song <yhs@fb.com>, Alexei Starovoitov <ast@kernel.org>,
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On Mon, Jul 18, 2022 at 12:34 PM Yosry Ahmed <yosryahmed@google.com> wrote:
>
[...]
>
> I think I figured this one out (the CI failure). I set max_entries for
> the maps in the test to 10, because I have 1 entry per-cgroup, and I
> have less than 10 cgroups. When I run the test with other tests I
> *think* there are other cgroups that are being created, so the number
> exceeds 10, and some of the entries for the test cgroups cannot be
> created.

Using hashmap to store per-cgroup data is only a short-term solution.
We should work on extending cgroup-local storage to tracing programs.
Maybe as a follow-up change once cgroup_iter is merged.

> in the bpf trace produced by my test, and the error turned out to be
> -E2BIG. I increased max_entries to 100 and it seems to be consistently
> passing when run with all the other tests, using both test_progs and
> test_progs-no_alu32.
>
> Please find a diff attached fixing this problem and a few other nits:
> - Return meaningful exit codes from the reclaimer() child process and
> check them in induce_vmscan().
> - Make buf and path variables static in get_cgroup_vmscan_delay()
> - Print error code in bpf trace when we fail to create a bpf map entry.
> - Print 0 instead of -1 when we can't find a map entry, to avoid
> underflowing the unsigned counters in the test.
>
> Let me know if this diff works or not, and if I need to send a new
> version with the diff or not. Also let me know if this fixes the
> failures that you have been seeing locally (which looked different
> from the CI failures).
>

Yosry, I also need to address Yonghong's comments in the cgroup_iter
patch, so we need to send v4 anyway.

Hao

> Thanks!
>
[...]