Re: [PATCH v7 7/7] mm: madvise: Avoid split during MADV_PAGEOUT and MADV_COLD

[David Hildenbrand]

On 08.04.24 20:39, Ryan Roberts wrote:
> Rework madvise_cold_or_pageout_pte_range() to avoid splitting any large
> folio that is fully and contiguously mapped in the pageout/cold vm
> range. This change means that large folios will be maintained all the
> way to swap storage. This both improves performance during swap-out, by
> eliding the cost of splitting the folio, and sets us up nicely for
> maintaining the large folio when it is swapped back in (to be covered in
> a separate series).
>
> Folios that are not fully mapped in the target range are still split,
> but note that behavior is changed so that if the split fails for any
> reason (folio locked, shared, etc) we now leave it as is and move to the
> next pte in the range and continue work on the proceeding folios.
> Previously any failure of this sort would cause the entire operation to
> give up and no folios mapped at higher addresses were paged out or made
> cold. Given large folios are becoming more common, this old behavior
> would have likely lead to wasted opportunities.
>
> While we are at it, change the code that clears young from the ptes to
> use ptep_test_and_clear_young(), via the new mkold_ptes() batch helper
> function. This is more efficent than get_and_clear/modify/set,
> especially for contpte mappings on arm64, where the old approach would
> require unfolding/refolding and the new approach can be done in place.
>
> Reviewed-by: Barry Song <v-songbaohua@xxxxxxxx>
> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
> ---

Acked-by: David Hildenbrand <david@xxxxxxxxxx>

--
Cheers,

David / dhildenb