Re: [RFC PATCH v4 4/4] selftest/bpf: add selftest for BPF based THP order seletection

[Yafang Shao <laoar.shao@gmail.com>]

On Tue, Jul 29, 2025 at 11:36 PM Zi Yan <ziy@nvidia.com> wrote:
>
> On 29 Jul 2025, at 5:18, Yafang Shao wrote:
>
> > This self-test verifies that PMD-mapped THP allocation is restricted in
> > page faults for tasks within a specific cgroup, while still permitting
> > THP allocation via khugepaged.
> >
> > Since THP allocation depends on various factors (e.g., system memory
> > pressure), using the actual allocated THP size for validation is
> > unreliable. Instead, we check the return value of get_suggested_order(),
> > which indicates whether the system intends to allocate a THP, regardless of
> > whether the allocation ultimately succeeds.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> > ---
> >  tools/testing/selftests/bpf/config            |   2 +
> >  .../selftests/bpf/prog_tests/thp_adjust.c     | 183 ++++++++++++++++++
> >  .../selftests/bpf/progs/test_thp_adjust.c     |  69 +++++++
> >  .../bpf/progs/test_thp_adjust_failure.c       |  24 +++
> >  4 files changed, 278 insertions(+)
> >  create mode 100644 tools/testing/selftests/bpf/prog_tests/thp_adjust.c
> >  create mode 100644 tools/testing/selftests/bpf/progs/test_thp_adjust.c
> >  create mode 100644 tools/testing/selftests/bpf/progs/test_thp_adjust_failure.c
> >
>
> The program below will only work on architectures with 4KB base page
> and PMD order is 9. It is better to read base page size and PMD page size
> from the system.

Thanks for the suggestion. I’ll change it.

-- 
Regards
Yafang