Re: [PATCH v2] ksm_tests: Skip hugepage test when Transparent Hugepages are disabled

[Li Wang <liwang@redhat.com>]

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Hi David,

On Tue, Jun 24, 2025 at 4:25 PM David Hildenbrand <david@redhat.com> wrote:

> On 24.06.25 05:27, Li Wang wrote:
> > Some systems (e.g. minimal or real-time kernels) may not enable
> > Transparent Hugepages (THP), causing MADV_HUGEPAGE to return EINVAL.
> > This patch introduces a runtime check using the existing THP sysfs
> > interface and skips the hugepage merging test (`-H`) when THP is
> > not available.
> >
> > To avoid those failures:
>
> But we deliberately have in tools/testing/selftests/mm/config:
>
> CONFIG_TRANSPARENT_HUGEPAGE=y
>
> So isn't this rather a test setup issue? Meaning, the environment is
> not well prepared.
>

It's true that CONFIG_TRANSPARENT_HUGEPAGE=y is explicitly
enabled in tools/testing/selftests/mm/config, so ideally the runtime
environment should also support THP.

However, in practice, we've found that on some systems:

- THP is disabled at boot time (transparent_hugepage=never)
- Or manually disabled via sysfs
- Or unavailable in RT kernels, containers, or minimal CI environments

In these cases, the test will fail with EINVAL on madvise(MADV_HUGEPAGE),
even though the kernel config is correct.

To make the test suite more robust and avoid false negatives, this patch
adds a runtime check for /sys/kernel/mm/transparent_hugepage/enabled.

If THP is not available, the hugepage test (-H) is skipped with a clear
message.


-- 
Regards,
Li Wang

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