On Thu, May 09, 2024 at 05:46:55AM -0700, Christoph Hellwig wrote:
> On Thu, May 09, 2024 at 12:31:07PM +0000, Pankaj Raghav (Samsung) wrote:
> > > Well, that's why I suggest doing it at mount time. Asking for it deep
> > > down in the write code is certainly going to be a bit problematic.
> >
> > Makes sense. But failing to mount because we can't get a huge zero folio
> > seems wrong as we still can't guarantee it even at mount time.
> >
> > With the current infrastructure I don't see anyway of geting a huge zero
> > folio that is guaranteed so that we don't need any fallback.
>
> You export get_huge_zero_page, put_huge_zero_page (they might need a
> rename and kerneldoc for the final version) and huge_zero_folio or a
> wrapper to get it, and then call get_huge_zero_page from mount,
static bool get_huge_zero_page(void)
{
struct folio *zero_folio;
retry:
if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
return true;
zero_folio = folio_alloc((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
HPAGE_PMD_ORDER);
if (!zero_folio) {
We might still fail here during mount. My question is: do we also fail
the mount if folio_alloc fails?
count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
return false;
}
...
> from unmount and just use huge_zero_folio which is guaranteed to
> exist once get_huge_zero_page succeeded.
>
--
Pankaj Raghav
