Messages in this thread | | | Date | Mon, 23 Jan 2023 14:24:13 +0100 | Subject | Re: [PATCH v7 2/8] iov_iter: Add a function to extract a page list from an iterator | From | David Hildenbrand <> |
| |
On 23.01.23 14:19, David Howells wrote: > David Hildenbrand <david@redhat.com> 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
| |