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    SubjectRe: [PATCH 00/10] mm: Linux VM Infrastructure to support Memory Power Management
    I was kinda hoping for something a bit simpler than that.  I'd boil down
    what you were saying to this:

    1. The kernel must be aware of how the pieces of hardware are
    mapped in to the system's physical address space
    2. The kernel must have a mechanism in place to minimize access to
    specific pieces of hardware
    3. For destructive power-down operations, the kernel should have a
    mechanism in place to ensure that no valuable data is contained
    in the memory to be powered down.

    Is that complete?

    On Wed, 2011-06-29 at 18:30 +0530, Ankita Garg wrote:
    > 1) Dynamic Power Transition: The memory controller can have the ability
    > to automatically transition regions of memory into lower power states
    > when they are devoid of references for a pre-defined threshold amount of
    > time. Memory contents are preserved in the low power states and accessing
    > memory that is at a low power state takes a latency hit.
    > 2) Dynamic Power Off: If a region is free/unallocated, the software can
    > indicate to the controller to completely turn off power to a certain
    > region. Memory contents are lost and hence the software has to be
    > absolutely sure about the usage statistics of the particular region. This
    > is a runtime capability, where the required amount of memory can be
    > powered 'ON' to match the workload demands.
    > 3) Partial Array Self-Refresh (PASR): If a certain regions of memory is
    > free/unallocated, the software can indicate to the controller to not
    > refresh that region when the system goes to suspend-to-ram state and
    > thereby save standby power consumption.

    (3) is simply a subset of (2), but with the additional restriction that
    the power off can only occur during a suspend operation.

    Let's say we fully implemented support for (2). What would be missing
    to support PASR?

    -- Dave

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