David Hildenbrand <david@xxxxxxxxxx> wrote: > 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 :) Well, it simplifies things a bit. I can make the new iov_iter_extract_pages() just do "pin" or "don't pin" and do no ref-getting at all. Things can be converted over to "unpin the pages or doing nothing" as they're converted over to using iov_iter_extract_pages() from iov_iter_get_pages*(). The block bio code then only needs a single bit of state: pinned or not pinned. For cifs RDMA, do I need to make it pass in FOLL_LONGTERM? And does that need a special cleanup? sk_buff fragment handling could still be tricky. I'm thinking that in that code I'll need to store FOLL_GET/PIN in the bottom two bits of the frag page pointer. Sometimes it allocates a new page and attaches it (have ref); sometimes it does zerocopy to/from a page (have pin) and sometimes it may be pointing to a kernel buffer (don't pin or ref). David
