Re: ZONE_DEVICE refcounting

Alistair Popple
2024-03-21T05:36:44Z

Alistair Popple <apopple@nvidia.com> writes:

> Dan Williams <dan.j.williams@intel.com> writes:
>
>> Alistair Popple wrote:
>
> I also noticed folio_anon() is not safe to call on a FS DAX page due to
> sharing PAGE_MAPPING_DAX_SHARED.

Also it feels like I could be missing something here. AFAICT the
page->mapping and page->index fields can't actually be used outside of
fs/dax because they are overloaded for the shared case. Therefore
setting/clearing them could be skipped and the only reason for doing so
is so dax_associate_entry()/dax_disassociate_entry() can generate
warnings which should never occur anyway. So all that code is
functionally unnecessary.

I guess that makes sense because DAX pages aren't in the pagecache or
LRU and therefore nothing tries to look them up via the normal
rmap. Does that sounds about right or did I miss something?

- Alistair