Re: [PATCH 1/1] mm/hugetlb: do not dissolve gigantic pages without runtime support

[Longlong Xia]

在 2026/8/19 16:52, David Hildenbrand (Arm) 写道:
> On 8/17/26 18:20, Longlong Xia wrote:
> > From: Longlong Xia <xialonglong@xxxxxxxxxx>
> >
> > dissolve_free_hugetlb_folio() doesn't check hstate_is_gigantic_no_runtime(h)
> > though remove_hugetlb_folio()/update_and_free_hugetlb_folio() silently
> > bail for such folios
> That's odd. Why do they silently skip such folios instead of warning that
> something unexpected is happening?
>
> This screams for a cleanup unless I am missing something :)
Because until this patch, dissolve_free_hugetlb_folio() was the one caller
that didn't filter hstate_is_gigantic_no_runtime() upstream. A WARN
would have fired on a real path: hotplug or hwpoison dissolving
a boot gigantic page on a no-runtime arch. So it had to stay silent.


This patch guards that last caller. The rest either check
hstate_is_gigantic_no_runtime() before calling, or operate on folios that
can't be gigantic_no_runtime (surplus/temporary gigantic folios aren't
created once alloc_gigantic_frozen_folio() returns NULL).

With the gap closed the bail can become a VM_WARN_ON_ONCE:

  // mm/hugetlb.c:1401  remove_hugetlb_folio
  if (hstate_is_gigantic_no_runtime(h)) {
+       /* Callers must filter gigantic_no_runtime upstream. */
+       VM_WARN_ON_ONCE(1);
        return;
  }

  // mm/hugetlb.c:1463  __update_and_free_hugetlb_folio
  if (hstate_is_gigantic_no_runtime(h)) {
+       /* Callers must filter gigantic_no_runtime upstream. */
+       VM_WARN_ON_ONCE(1);
        return;
  }

Separate follow-up, or fold into a v2 of this patch?

Thanks,

Longlong