Re: [PATCH v22 1/4] mm: add MAP_DROPPABLE for designating always lazily freeable mappings

David Hildenbrand
2024-07-11T19:22:06Z

On 11.07.24 21:17, Linus Torvalds wrote:
> On Thu, 11 Jul 2024 at 12:08, David Hildenbrand <david@redhat.com> wrote:
>>
>> We also have these folio_mark_dirty() calls, for example in
>> unpin_user_pages_dirty_lock(). Hm ... so preventing the folio from
>> getting dirtied is likely shaky.
>
> I do wonder if we should just disallow page pinning for these pages
> entirely. When the page can get replaced by zeroes at any time,
> pinning it doesn't make much sense.
>
> Except we do have that whole "fast" case that intentionally doesn't
> take locks and doesn't have a vma. Darn.

Yeah, and I think it should all be simpler; we shouldn't have to
special-case these cases everywhere.

Maybe we can just find a way to not do *folio_set_swapbacked() without a
VMA.

--
Cheers,

David / dhildenb