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    SubjectRe: VM_RESERVED [was Re: mapping user space buffer to kernel address space]

    On Fri, 20 Oct 2000, Andrea Arcangeli wrote:
    > The page count of the mapped pages should be ok, it seems those mapped pages
    > have a reference count of 1 just from the vmalloc allocation and they use
    > PG_reserved just to skip swap_out, but I feel safer too if the bttv maintainers
    > will check it and send it to you themself after checking it's correct. (I only
    > verified that it was compiling correctly)

    Note that the page count should _not_ be one: the page could should be

    Basically, the "nopage()" function has to do a "get_page(page)". But if
    the page is marked PG_reserved, that would hide a bug in a drievr that
    doesn't do that part.

    Also, I suspect some drivers do the "remap_page_range() one page at a
    time", and again exactly due to page count issues remap_page_range() will
    refuse to touch pages that aren't marked PG_reserved. So I wholeheartedly
    agree with your change, but I just suspect it will break drivers that have
    depended on the fact that PG_reserved means that they can be lazy and not
    bother about getting all the details right.

    Not that I mind breaking drivers in general, but not right now.


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