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    SubjectRe: fix iounmap and a pageattr memleak (x86 and x86-64)
    On Tue, Nov 02, 2004 at 05:34:08PM -0500, Jason Baron wrote:
    > I've seen the page_count being -1 (not sure why), for a number of pages in
    > the identity mapped region...So the BUG() on 0 doesn't seem valid to me.

    bugcheck on 0 is valid there, it signals memleak. page_count == -1
    signals another bug that might or might not be fixed by this as far as I
    can tell (this furthermore is a pte, so it sure can't have page_count ==
    0 or -1). So please try to track down which pages had page_count == -1.

    Note, we must not confuse page->count with page_count, for the former
    value -1 means "in the freelist". For the latter it signals a bug.

    > Also, in order to tell if the pages should be merged back to create a huge
    > page, i don't see how the patch differentiates b/w pages that were split
    > and those that weren't simply based on the page_count....

    that's a page_count of the _pte_, not of the pages. so we're guaranteed
    it's always 1 unless we deal with this very pageattr code that is the
    only one that evers boost a pte page_count to > 1.

    If you mean how can we provide an universal API with only keeping track
    of things with the page_count of the pte, we can't, and that's why it's
    not an universal API and that's why some symmetry is required by the
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