Re: [PATCH 4/5] bio: introduce BIO_FOLL_PIN flag

[Christoph Hellwig]

On Fri, Aug 21, 2020 at 09:20:58PM -0700, John Hubbard wrote:
> Add a new BIO_FOLL_PIN flag to struct bio, whose "short int" flags field
> was full, thuse triggering an expansion of the field from 16, to 32
> bits. This allows for a nice assertion in bio_release_pages(), that the
> bio page release mechanism matches the page acquisition mechanism.
> 
> Set BIO_FOLL_PIN whenever pin_user_pages_fast() is used, and check for
> BIO_FOLL_PIN before using unpin_user_page().

When would the flag not be set when BIO_NO_PAGE_REF is not set?

Also I don't think we can't just expand the flags field, but I can send
a series to kill off two flags.