Re: [PATCH v3] ksm: use range-walk function to jump over holes in scan_get_next_rmap_item

[David Hildenbrand]

On 16.10.25 03:22, Pedro Demarchi Gomes wrote:
> Currently, scan_get_next_rmap_item() walks every page address in a VMA
> to locate mergeable pages. This becomes highly inefficient when scanning
> large virtual memory areas that contain mostly unmapped regions.
>
> This patch replaces the per-address lookup with a range walk using
> walk_page_range(). The range walker allows KSM to skip over entire
> unmapped holes in a VMA, avoiding unnecessary lookups.
> This problem was previously discussed in [1].
>
> [1] https://lore.kernel.org/linux-mm/423de7a3-1c62-4e72-8e79-19a6413e420c@xxxxxxxxxx/
>
> ---
>
> v3:
>    - Treat THPs in ksm_pmd_entry
>    - Update ksm_scan.address outside walk_page_range
>    - Change goto to while loop
>
> v2: https://lore.kernel.org/all/20251014151126.87589-1-pedrodemargomes@xxxxxxxxx/
>    - Use pmd_entry to walk page range
>    - Use cond_resched inside pmd_entry()
>    - walk_page_range returns page+folio
>
> v1: https://lore.kernel.org/all/20251014055828.124522-1-pedrodemargomes@xxxxxxxxx/
>
> Reported-by: craftfever <craftfever@xxxxxxxxxx>
> Closes: https://lkml.kernel.org/r/020cf8de6e773bb78ba7614ef250129f11a63781@xxxxxxxxx
> Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Pedro Demarchi Gomes <pedrodemargomes@xxxxxxxxx>
> ---

This patch will need some more work.

@Andrew, please drop it for now.

--
Cheers

David / dhildenb