Re: [PATCH mm-new v2 1/1] mm/khugepaged: abort collapse scan on non-swap entries

[Lance Yang]

On 2025/10/1 16:31, David Hildenbrand wrote:
> On 01.10.25 05:22, Lance Yang wrote:
> > From: Lance Yang <lance.yang@xxxxxxxxx>
> >
> > Currently, special non-swap entries (like migration, hwpoison, or PTE
> > markers) are not caught early in hpage_collapse_scan_pmd(), leading to
> > failures deep 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 any one is found, the scan is aborted immediately with the
> > SCAN_PTE_NON_PRESENT result, as Lorenzo suggested[2], avoiding wasted
> > work.
> >
> > [1] https://lore.kernel.org/linux-mm/7840f68e-7580-42cb- 
> > a7c8-1ba64fd6df69@xxxxxxxxxx
> > [2] https://lore.kernel.org/linux-mm/7df49fe7-c6b7-426a-8680- 
> > dcd55219c8bd@lucifer.local
> >
> > Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
> > Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
> > Signed-off-by: Lance Yang <lance.yang@xxxxxxxxx>
> > ---
>
> Could have mentioned you adjust the flow of code to resemble what we 
> have in __collapse_huge_page_isolate().

Thanks for pointing that out! Let's do that separately. I'm working
on a follow-up patch that will unify the scanning with the
almost-duplicated code as you suggested ;)

> Acked-by: David Hildenbrand <david@xxxxxxxxxx>

Cheers!