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    SubjectRe: [PATCH 0/4] Swap migration V3: Overview
    Andrew Morton wrote:
    > Christoph Lameter <clameter@sgi.com> wrote:
    >
    >>Page migration is also useful for other purposes:
    >>
    >> 1. Memory hotplug. Migrating processes off a memory node that is going
    >> to be disconnected.
    >>
    >> 2. Remapping of bad pages. These could be detected through soft ECC errors
    >> and other mechanisms.
    >
    >
    > It's only useful for these things if it works with close-to-100% reliability.
    >
    > And there are are all sorts of things which will prevent that - mlock,
    > ongoing direct-io, hugepages, whatever.
    >
    In lhms tree, current status is below: (If I'm wrong, plz fix)
    ==
    For mlock, direct page migration will work fine. try_to_unmap_one()
    in -mhp tree has an argument *force* and ignore VM_LOCKED, it's for this.

    For direct-io, we have to wait for completion.
    The end of I/O is not notified and memory_migrate() is just polling pages.

    For hugepages, we'll need hugepage demand paging and more work, I think.
    ==

    When a process migrates to other nodes by hand, it can cooperate with migration
    subsystem. So we don't have to be afraid of some special using of memory, in many case.
    I think Christoph's approach will work fine.

    When it comes to memory-hotplug, arbitrary processes are affected.
    It's more difficult.

    We should focus on 'process migraion on demand', in this thread.

    -- Kame

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