Re: [PATCH v4 7/7] selftests: prctl: introduce tests for disabling THPs except for madvise

[Lorenzo Stoakes]

On Wed, Aug 13, 2025 at 06:24:11PM +0200, David Hildenbrand wrote:
> > > +
> > > +FIXTURE_SETUP(prctl_thp_disable_except_madvise)
> > > +{
> > > +	if (!thp_available())
> > > +		SKIP(return, "Transparent Hugepages not available\n");
> > > +
> > > +	self->pmdsize = read_pmd_pagesize();
> > > +	if (!self->pmdsize)
> > > +		SKIP(return, "Unable to read PMD size\n");
> > > +
> > > +	if (prctl(PR_SET_THP_DISABLE, 1, PR_THP_DISABLE_EXCEPT_ADVISED, NULL, NULL))
> > > +		SKIP(return, "Unable to set PR_THP_DISABLE_EXCEPT_ADVISED\n");
> >
> > This should be a test fail I think, as the only ways this could fail are
> > invalid flags, or failure to obtain an mmap write lock.
>
> Running a kernel that does not support it?

I can't see anything in the kernel to #ifdef it out so I suppose you mean
running these tests on an older kernel?

But this is an unsupported way of running self-tests, they are tied to the
kernel version in which they reside, and test that specific version.

Unless I'm missing something here?

>
> We could check the errno to distinguish I guess.

Which one? manpage says -EINVAL, but can also be due to incorrect invocation,
which would mean a typo could mean tests pass but your tests do nothing :)

>
> --
> Cheers,
>
> David / dhildenb
>