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    SubjectRe: [PATCH v4 21/23] mm: use custom page_free for P2PDMA pages
    On Wed, Nov 17, 2021 at 02:54:08PM -0700, Logan Gunthorpe wrote:
    > When P2PDMA pages are passed to userspace, they will need to be
    > reference counted properly and returned to their genalloc after their
    > reference count returns to 1. This is accomplished with the existing
    > DEV_PAGEMAP_OPS and the .page_free() operation.
    >
    > Change CONFIG_P2PDMA to select CONFIG_DEV_PAGEMAP_OPS and add
    > MEMORY_DEVICE_PCI_P2PDMA to page_is_devmap_managed(),
    > devmap_managed_enable_[put|get]() and free_devmap_managed_page().

    Uuuh. We are trying hard to kill off this magic free at refcount 1
    behavior in the amdgpu device coherent series. We really should not
    add more of this.

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