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    SubjectRe: [PATCH] Add support for usbfs zerocopy.
    On Wed, Jan 06, 2016 at 10:35:05AM -0500, Alan Stern wrote:
    > Indeed, the I/O operations we are using with mmap here are not reads or
    > writes; they are ioctls. As far as I know, the kernel doesn't have any
    > defined interface for zerocopy ioctls.

    IF it was using mmap for I/O it would read in through the page fault
    handler an then mark the page dirty for writeback by the VM. Thats
    clearly not the case.

    Instead it's using mmap on a file as a pecial purpose anonymous
    memory allocator, bypassing the VM and VM policies, including
    allowing to pin kernel memory that way.

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