Re: [PATCH v2 0/7] convert most filesystems to pin_user_pages_fast()

John Hubbard
2022-09-06T07:11:04Z

On 9/5/22 23:36, Christoph Hellwig wrote:
> On Tue, Aug 30, 2022 at 09:18:36PM -0700, John Hubbard wrote:
>> The conversion is temporarily guarded by
>> CONFIG_BLK_USE_PIN_USER_PAGES_FOR_DIO. In the future (not part of this
>> series), when we are certain that all filesystems have converted their
>> Direct IO paths to FOLL_PIN, then we can do the final step, which is to
>> get rid of CONFIG_BLK_USE_PIN_USER_PAGES_FOR_DIO and search-and-replace
>> the dio_w_*() functions with their final names (see bvec.h changes).
>
> What is the the point of these wrappers? We should be able to
> convert one caller at a time in an entirely safe way.

I would be delighted if that were somehow possible. Every time I think
it's possible, it has fallen apart. The fact that bio_release_pages()
will need to switch over from put_page() to unpin_user_page(), combined
with the fact that there are a lot of callers that submit bios, has
led me to the current approach.

What did you have in mind?

thanks,

--
John Hubbard
NVIDIA