Re: [PATCH v7 2/8] iov_iter: Add a function to extract a page list from an iterator

[David Hildenbrand]

On 23.01.23 14:19, David Howells wrote:
> David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> > Switching from FOLL_GET to FOLL_PIN was in the works by John H. Not sure what
> > the status is. Interestingly, Documentation/core-api/pin_user_pages.rst
> > already documents that "CASE 1: Direct IO (DIO)" uses FOLL_PIN ... which does,
> > unfortunately, no reflect reality yet.
>
> Yeah - I just came across that.
>
> Should iov_iter.c then switch entirely to using pin_user_pages(), rather than
> get_user_pages()?  In which case my patches only need keep track of
> pinned/not-pinned and never "got".

That would be the ideal case: whenever intending to access page content, 
use FOLL_PIN instead of FOLL_GET.

The issue that John was trying to sort out was that there are plenty of 
callsites that do a simple put_page() instead of calling 
unpin_user_page(). IIRC, handling that correctly in existing code -- 
what was pinned must be released via unpin_user_page() -- was the 
biggest workitem.

Not sure how that relates to your work here (that's why I was asking): 
if you could avoid FOLL_GET, that would be great :)

--
Thanks,

David / dhildenb