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    SubjectRe: [PATCH] Add __GFP_MOVABLE for callers to flag allocations that may be migrated
    On Mon, 4 Dec 2006 11:41:42 -0800 (PST)
    Christoph Lameter <clameter@sgi.com> wrote:

    > > That depends on how we do hot-unplug, if we do it. I continue to suspect
    > > that it'll be done via memory zones: effectively by resurrecting
    > > GFP_HIGHMEM. In which case there's little overlap with anti-frag. (btw, I
    > > have a suspicion that the most important application of memory hot-unplug
    > > will be power management: destructively turning off DIMMs).
    >
    > There are numerous other uses as well (besides DIMM and node unplug):
    >
    > 1. Faulty DIMM isolation
    > 2. Virtual memory managers can reduce memory without resorting to
    > balloons.
    > 3. Physical removal and exchange of memory while a system is running
    > (Likely necessary to complement hotplug cpu, cpus usually come
    > with memory).
    >
    > The multi zone approach does not work with NUMA. NUMA only supports a
    > single zone for memory policy control etc.

    Wot? memory policies are a per-vma thing?

    Plus NUMA of course supports more that a single zone. Perhaps you meant
    one zone per node. If you did, that's a pretty dumb-sounding restriction
    and I don't know where you got it from.

    > Also multiple zones carry with
    > it a management overhead that is unnecessary for the MOVABLE/UNMOVABLE
    > distinction.

    I suspect you'll have to live with that. I've yet to see a vaguely sane
    proposal to otherwise prevent unreclaimable, unmoveable kernel allocations
    from landing in a hot-unpluggable physical memory region.
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