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    SubjectRe: [PATCH v5 00/12] vfio, dax: prevent long term filesystem-dax pins and other fixes
    On Fri, Mar 2, 2018 at 2:10 PM, Christoph Hellwig <hch@lst.de> wrote:
    > I really don't like these IS_DEVDAX and IS_FSDAX flags. We should
    > stop pretending DAX is a global per-inode choice and get rid of these
    > magic flags entirely. So please convert the instances inside the
    > various file systems to checking the file system mount options instead.
    >
    > For the core ones we'll need to differentiate:
    >
    > - the checks in generic_file_read_iter and __generic_file_write_iter
    > seem to not be needed anymore at all since we stopped abusing the
    > direct I/O code for DAX, so they should probably be removed.
    > - io_is_direct is a weird check and should probably just go away,
    > as there is not point in always setting IOCB_DIRECT for DAX I/O
    > - fadvise should either become a file op, or a flag on the inode that
    > fadvice is supported instead of the nasty noop_backing_dev_info or
    > DAX check.
    > - Ditto for madvise
    > - vma_is_dax should probably be replaced with a VMA flag.
    > - thp_get_unmapped_area I don't really understand why we have a dax
    > check there.
    > - dax_mapping will be much harder to sort out.
    >
    > But all these DAX flags certainly look like a major hodge podge to me.

    They are indeed a hodge-podge. The problem is that the current
    IS_DAX() is broken. So I'd like to propose fixing IS_DAX() with
    IS_FSDAX() + IS_DEVDAX() for 4.16-rc4 and queue up these wider reworks
    you propose for the next merge window.

    Acceptable?

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