Re: [PATCH 1/1] mm: prevent poison consumption when splitting THP

[Wei Yang]

On Mon, Sep 29, 2025 at 09:34:12AM +0200, David Hildenbrand wrote:
>On 28.09.25 05:28, Qiuxu Zhuo wrote:
[...]
>
>Hm, I wonder if we should actually check in try_to_map_unused_to_zeropage()
>whether the page has the hwpoison flag set. Nothing wrong with scanning
>non-affected pages.
>
>In thp_underused() we should just skip the folio entirely I guess, so keep
>it simple.
>
>So what about something like this:
>
>diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>index 9c38a95e9f091..d4109fd7fa1f2 100644
>--- a/mm/huge_memory.c
>+++ b/mm/huge_memory.c
>@@ -4121,6 +4121,9 @@ static bool thp_underused(struct folio *folio)
>        if (khugepaged_max_ptes_none == HPAGE_PMD_NR - 1)
>                return false;
>+       folio_contain_hwpoisoned_page(folio)
>+               return false;
>+

One question.

When hardware detect error, it would immediately trigger memory_failure()? Or
it will wait until the memory is accessed?

>        for (i = 0; i < folio_nr_pages(folio); i++) {
>                kaddr = kmap_local_folio(folio, i * PAGE_SIZE);
>                if (!memchr_inv(kaddr, 0, PAGE_SIZE)) {
>diff --git a/mm/migrate.c b/mm/migrate.c
>index 9e5ef39ce73af..393fc2ffc96e5 100644
>--- a/mm/migrate.c
>+++ b/mm/migrate.c
>@@ -305,8 +305,9 @@ static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw,
>        pte_t newpte;
>        void *addr;
>-       if (PageCompound(page))
>+       if (PageCompound(page) || PageHWPoison(page))
>                return false;
>+
>        VM_BUG_ON_PAGE(!PageAnon(page), page);
>        VM_BUG_ON_PAGE(!PageLocked(page), page);
>        VM_BUG_ON_PAGE(pte_present(ptep_get(pvmw->pte)), page);
>
>
>-- 
>Cheers
>
>David / dhildenb
>

-- 
Wei Yang
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