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    SubjectRe: [PATCH v4 21/23] mm: use custom page_free for P2PDMA pages


    On 2021-12-21 2:06 a.m., Christoph Hellwig wrote:
    > 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.

    Ah, ok. I found Ralph's patch that cleans this up and I can try to
    rebase this onto it for future postings until it gets merged.

    Your other comments I can address for the next time I post this series.

    Thanks for the review!

    Logan

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