Messages in this thread | | | Date | Mon, 23 Jan 2023 15:20:41 +0100 | Subject | Re: [PATCH v7 2/8] iov_iter: Add a function to extract a page list from an iterator | From | David Hildenbrand <> |
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On 23.01.23 14:38, David Howells wrote: > David Hildenbrand <david@redhat.com> 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.
Unfortunately, I'll have to let BIO experts comment on that :) I only know the MM side of things here.
> > For cifs RDMA, do I need to make it pass in FOLL_LONGTERM? And does that need > a special cleanup?
Anything that holds pins "possibly forever" should that. vmsplice() is another example that should use it, once properly using FOLL_PIN. [FOLL_GET | FOLL_LONGTERM is not really used/defined with semantics]
> > 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 >
-- Thanks,
David / dhildenb
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