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
