Re: [PATCH v3 15/18] mm/huge_memory: lift order-0 restriction for swapcache split

[Kairui Song]

On Fri, Aug 28, 2026 at 12:51 AM David Hildenbrand (Arm)
<david@xxxxxxxxxx> wrote:
>
> On 8/20/26 20:55, Kairui Song via B4 Relay wrote:
> > From: Kairui Song <kasong@xxxxxxxxxxx>
> >
> > 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.
> >
> > Acked-by: Zi Yan <ziy@xxxxxxxxxx>
> > Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
> > ---
>
> In contrast to the other cleanup patches, this patch changes behavior.
>
> I would suggest to send all cleanups first, and send this out separately, such
> that it gets proper attention and doesn't get buried in a sequence of
> harmlessly-looking cleanups :)

No problem, send this later then :)