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    SubjectRe: [patch 4/6] mm: merge populate and nopage into fault (fixes nonlinear)
    On Wed, Mar 07, 2007 at 10:32:22AM +0100, Peter Zijlstra wrote:
    > On Wed, 2007-03-07 at 01:07 -0800, Andrew Morton wrote:
    > > On Wed, 07 Mar 2007 09:51:57 +0100 Miklos Szeredi <miklos@szeredi.hu> wrote:
    > >
    > > > > > Dirty page accounting doesn't work either on
    > > > > > non-linear mappings
    > > > >
    > > > > It doesn't? Confused - these things don't have anything to do with each
    > > > > other do they?
    > > >
    > > > Look in page_mkclean(). Where does it handle non-linear mappings?
    > > >
    > >
    > > OK, I'd forgotten about that. It won't break dirty memory accounting,
    > > but it'll potentially break dirty memory balancing.
    > >
    > > If we have the wrong page (due to nonlinear), page_check_address() will
    > > fail and we'll leave the pte dirty. That puts us back to the pre-2.6.17
    > > algorithms and I guess it'll break the msync guarantees.
    > >
    > > Peter, I thought we went through the nonlinear problem ages ago and decided
    > > it was OK?
    >
    > Can recollect as much, I modelled it after page_referenced() and can't
    > find any VM_NONLINEAR specific code in there either.
    >
    > Will have a hard look, but if its broken, then page_referenced if
    > equally broken it seems, which would make page reclaim funny in the
    > light of nonlinear mappings.

    page_referenced is just an heuristic, and it ignores nonlinear mappings
    and the page which will get filtered down to try_to_unmap.

    Page reclaim is already "funny" for nonlinear mappings, page_referenced
    is the least of its worries ;) It works, though.


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