Re: [PATCH v8 08/15] hugetlb: Use the has_hwpoisoned flag

[Matthew Wilcox <willy@infradead.org>]

On Tue, Aug 04, 2026 at 12:28:06PM -0400, Gregory Price wrote:
> Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>

Thanks, will add.

> > -#if defined(CONFIG_MEMORY_FAILURE) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
> > +#if defined(CONFIG_MEMORY_FAILURE) && defined(CONFIG_LARGE_FOLIO)
> >  /*
> > - * PageHasHWPoisoned indicates that at least one subpage is hwpoisoned in the
> > - * compound page.
> > + * folio_has_hwpoisoned indicates that at least one page is hwpoisoned in the
> > + * folio.  That page will usually also have the HWPoison flag set, but this
> > + * is not possible for folios which have HVO (see memory-failure for the
> > + * scheme used in that case).  You probably don't want to call this directly;
> > + * use folio_has_hwpoisoned_page() instead.
> >   *
> >   * This flag is set by hwpoison handler.  Cleared by THP split or free page.
> >   */
> 
> Had to google HVO, and didn't see HVO directly mentioned in
> memory-failure.  Maybe worth expanding HVO to its actual definition and
> a sentence on the quirk.

It is mentioned earlier in the same file:

include/linux/page-flags.h:      * Limit mask usage to HugeTLB vmemmap optimization (HVO) where it

but that's not obvious when reading a patch.  I'll just expand it here:

 * The has_hwpoisoned flag indicates that at least one page is hwpoisoned
 * in the folio.  That page will usually also have the HWPoison flag
 * set, but this is not possible for folios which have HugeTLB vmemmap
 * optimization (see hugetlb_update_hwpoison() for the scheme used
 * in that case).  You probably don't want to call this directly; use
 * folio_has_hwpoisoned_page() instead.

> Does "Hugepage Vmapmem Optimization" just report poison for the head and
> we lose the sub-page poison information in general?

We only lose the sub-folio poison information if kmalloc fails in
hugetlb_update_hwpoison().  In the happy case, we retain knowledge
of which pages contain hwpoison (and later in this series, we actually
expose that information instead of just pretending the whole folio is
poisoned)