Re: [PATCH RFC 12/13] mm/huge_memory: lift order-0 restriction for swapcache split

On Fri Aug 7, 2026 at 5:17 PM EDT, Kairui Song via B4 Relay wrote:
> From: Kairui Song <[email protected]>
>
> The restriction that swapcache folios can only be uniformly split to
> order 0 dates back to when the swap cache was managed via address_space
> mapping (swap_address_space).  The old split loop only created order-0
> sub-folios with a fixed stride, so non-uniform split and non-zero order
> were rightfully blocked.
>
> After the swap cache switched to swap table under a cluster lock,
> __swap_cache_replace_folio already gained the ability to replace any
> number of entries for any sub-folio size in one cluster, and the old
> swap_address_space locking and limit was removed. The restriction
> became obsolete but persisted through multiple refactorings.
>
> Drop it now: swapcache folios can be split to any supported order with
> either uniform or non-uniform split, except order-1 which is not
> supported for anon folios. Mappingless swap cache folios could be either
> anon or shmem, so for now we just simply forbid order-1 for all swapcache.
>
> Signed-off-by: Kairui Song <[email protected]>
> ---
>  mm/huge_memory.c | 32 +++++++++++++-------------------
>  1 file changed, 13 insertions(+), 19 deletions(-)
>

LGTM. BTW, __split_huge_page_to_list_to_order()'s comment also needs an
update about splitting to order-1 folios.

Acked-by: Zi Yan <[email protected]>


-- 
Best Regards,
Yan, Zi