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    SubjectRe: Active Memory Defragmentation: Our implementation & problems
    >> There are a couple of special cases that might be feasible without making
    >> an ungodly mess. PTE pages spring to mind (particularly as they can be
    >> in highmem too). They should be reasonably easy to move (assuming we can
    >> use rmap to track them back to the process they belong to to lock them ...
    >> hmmm ....)
    >
    > We don't do any pte page reclaim at any time other than process exit and
    > there are plenty of pte pages we can just plain free anyway. Anthing
    > that's completely mapping page cache, for instance.
    >
    > In the replacement case, taking mm->page_table_lock, doing the copy, and
    > replacing the pointer from the pmd should be all that it takes. But, I
    > wonder if we could miss any sets of the pte dirty bit this way...

    As long as we make sure the process doesn't run during the move, I don't
    see why it'd be a problem. But I am less than convinced that rmap will
    lead us back from the PTE page to the mm, at least w/o modification.

    M.

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