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

[Gregory Price <gourry@gourry.net>]

On Fri, Jul 31, 2026 at 09:07:53PM +0100, Matthew Wilcox (Oracle) wrote:
> Other large folios use the has_hwpoisoned flag.  Convert hugetlb to match.
> This will help us use the per-page hwpoison flag in the future.
> 
> Also introduce a folio_test_huge_poison().  This has exactly the same
> meaning as folio_test_has_hwpoisoned() but can be used when we don't have
> a reference to the folio containing the page.  folio_test_has_hwpoisoned()
> can race with folio splitting / reallocation and trip the assertions
> in const_folio_flags().
> 
> This closes a gap where a page in a previously-poisoned hugetlb folio
> could be observed to not have the hwpoison bit set.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

one question inline, but this seems straightforward.

Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>

> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 4185a03a45cf..4fab3fbfd430 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -893,14 +893,19 @@ static inline int PageTransCompound(const struct page *page)
>  TESTPAGEFLAG_FALSE(TransCompound, transcompound)
>  #endif
>  
> -#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.

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

~Gregory