Re: [PATCH mm-new 1/1] mm/khugepaged: abort collapse scan on non-swap entries

[David Hildenbrand]

On 24.09.25 12:02, Lance Yang wrote:
> From: Lance Yang <lance.yang@xxxxxxxxx>
>
> The existing check in hpage_collapse_scan_pmd() is specific to uffd-wp
> markers. Other special markers (e.g., GUARD, POISONED) would not be caught
> early, leading to failures deeper in the swap-in logic.
>
> hpage_collapse_scan_pmd()
>   `- collapse_huge_page()
>       `- __collapse_huge_page_swapin() -> fails!
>
> As David suggested[1], this patch skips any such non-swap entries early.
> If a special marker is found, the scan is aborted immediately with the
> SCAN_PTE_NON_PRESENT result, as Lorenzo suggested[2], avoiding wasted
> work.

Note that I suggested to skip all non-present entries except swap 
entries, which includes migration entries, hwpoisoned entries etc.

--
Cheers

David / dhildenb