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    SubjectRe: [RFC PATCH 2/2] mm/gup: introduce vaddr_pin_pages_remote()
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    On 8/12/19 4:49 PM, Ira Weiny wrote:
    > On Sun, Aug 11, 2019 at 06:50:44PM -0700, john.hubbard@gmail.com wrote:
    >> From: John Hubbard <jhubbard@nvidia.com>
    ...
    >> diff --git a/drivers/infiniband/core/umem_odp.c b/drivers/infiniband/core/umem_odp.c
    >> index 53085896d718..fdff034a8a30 100644
    >> --- a/drivers/infiniband/core/umem_odp.c
    >> +++ b/drivers/infiniband/core/umem_odp.c
    >> @@ -534,7 +534,7 @@ static int ib_umem_odp_map_dma_single_page(
    >> }
    >>
    >> out:
    >> - put_user_page(page);
    >> + vaddr_unpin_pages(&page, 1, &umem_odp->umem.vaddr_pin);
    >>
    >> if (remove_existing_mapping) {
    >> ib_umem_notifier_start_account(umem_odp);
    >> @@ -635,9 +635,10 @@ int ib_umem_odp_map_dma_pages(struct ib_umem_odp *umem_odp, u64 user_virt,
    >> * complex (and doesn't gain us much performance in most use
    >> * cases).
    >> */
    >> - npages = get_user_pages_remote(owning_process, owning_mm,
    >> + npages = vaddr_pin_pages_remote(owning_process, owning_mm,
    >> user_virt, gup_num_pages,
    >> - flags, local_page_list, NULL, NULL);
    >> + flags, local_page_list, NULL, NULL,
    >> + &umem_odp->umem.vaddr_pin);
    >
    > Thinking about this part of the patch... is this pin really necessary? This
    > code is not doing a long term pin. The page just needs a reference while we
    > map it into the devices page tables. Once that is done we should get notifiers
    > if anything changes and we can adjust. right?
    >

    OK, now it's a little interesting: the FOLL_PIN is necessary, but maybe not
    FOLL_LONGTERM. Illustrating once again that it's actually necessary to allow
    these flags to vary independently.

    And that leads to another API refinement idea: let's set FOLL_PIN within the
    vaddr_pin_pages*() wrappers, and set FOLL_LONGTER in the *callers* of those
    wrappers, yes?

    thanks,
    --
    John Hubbard
    NVIDIA

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