Re: [PATCH v2 3/3] selftests/mm/charge_reserved_hugetlb: fix hugetlbfs mount size for large hugepages

[Li Wang <liwang@redhat.com>]

On Sun, Dec 21, 2025 at 5:49 PM David Hildenbrand (Red Hat)
<david@kernel.org> wrote:
>
> On 12/21/25 10:44, Li Wang wrote:
> > David Hildenbrand (Red Hat) <david@kernel.org> wrote:
> >> On 12/21/25 09:58, Li Wang wrote:
> >>> charge_reserved_hugetlb.sh mounts a hugetlbfs instance at /mnt/huge with
> >>> a fixed size of 256M. On systems with large base hugepages (e.g. 512MB),
> >>> this is smaller than a single hugepage, so the hugetlbfs mount ends up
> >>> with effectively zero capacity (often visible as size=0 in mount output).
> >>>
> >>> As a result, write_to_hugetlbfs fails with ENOMEM and the test can hang
> >>> waiting for progress.
> >>
> >> I'm curious, what's the history of using "256MB" in the first place (or
> >> specifying any size?).
> >
> > Seems the script initializes it with "256MB" from:
> >
> > commit 29750f71a9b4cfae57cdddfbd8ca287eddca5503
> > Author: Mina Almasry <almasrymina@google.com>
> > Date:   Wed Apr 1 21:11:38 2020 -0700
> >
> >      hugetlb_cgroup: add hugetlb_cgroup reservation tests
>
> What would happen if we don't specify a size at all?

It still works well, I have gone through the whole file and
there is no subtest that relies on the 256M capability.

So we could just:

    mount -t hugetlbfs -o pagesize=${MB}M none /mnt/huge

-- 
Regards,
Li Wang