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    SubjectRe: [PATCH 1/2] drm: add cache support for arm64
    On Thu, Aug 8, 2019 at 12:59 AM Christoph Hellwig <hch@lst.de> wrote:
    >
    > On Wed, Aug 07, 2019 at 10:30:04AM -0700, Rob Clark wrote:
    > > So, we do end up using GFP_HIGHUSER, which appears to get passed thru
    > > when shmem gets to the point of actually allocating pages.. not sure
    > > if that just ends up being a hint, or if it guarantees that we don't
    > > get something in the linear map.
    > >
    > > (Bear with me while I "page" this all back in.. last time I dug thru
    > > the shmem code was probably pre-armv8, or at least before I had any
    > > armv8 hw)
    >
    > GFP_HIGHUSER basically just means that this is an allocation that could
    > dip into highmem, in which case it would not have a kernel mapping.
    > This can happen on arm + LPAE, but not on arm64.

    Just a dumb question, but why is *all* memory in the linear map on
    arm64? It would seem useful to have a source of pages that is not in
    the linear map.
    I guess it is mapped as huge pages (or something larger than 4k pages)?

    Any recommended reading to understand how/why the kernel address space
    is setup the way it is (so I can ask fewer dumb questions)?

    BR,
    -R

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