Re: [PATCH] mm/huge_memory.c: introduce split_unmapped_folio_to_order

[Zi Yan <ziy@nvidia.com>]

On 13 Nov 2025, at 11:02, Lorenzo Stoakes wrote:

> On Thu, Nov 13, 2025 at 04:36:01PM +0100, Francois Dugast wrote:
>> Hi Balbir,
>>
>> On Wed, Nov 12, 2025 at 03:46:33PM +1100, Balbir Singh wrote:
>>> Unmapped was added as a parameter to __folio_split() and related
>>> call sites to support splitting of folios already in the midst
>>> of a migration. This special case arose for device private folio
>>> migration since during migration there could be a disconnect between
>>> source and destination on the folio size.
>>>
>>> Introduce split_unmapped_folio_to_order() to handle this special case.
>>> This in turn removes the special casing introduced by the unmapped
>>> parameter in __folio_split().
>>
>> Such a helper would be needed in drm_pagemap_migrate_to_devmem when
>> reallocating a device folio to smaller pages.
>>
>> Could we export it (EXPORT_SYMBOL)?

drm_pagemap_migrate_to_devmem() is a function defined in tree, you
just need to include huge_mm.h to use split_unmapped_folio_to_order().
Why do you need to export split_unmapped_folio_to_order()?

>
> As a rule we don't export things from core mm. And certainly not to non-GPL
> modules.
>
> Unless David feels very differently or there's some enormously compelling
> reason for it I'd really rather we didn't.


Best Regards,
Yan, Zi