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    SubjectRe: Frontswap [PATCH 0/4] (was Transcendent Memory): overview
    On 04/25/2010 04:37 PM, Dan Magenheimer wrote:
    >> My issue is with the API's synchronous nature. Both RAM and more
    >> exotic
    >> memories can be used with DMA instead of copying. A synchronous
    >> interface gives this up.
    >> :
    >> Let's not allow the urge to merge prevent us from doing the right
    >> thing.
    >> :
    >> I see. Given that swap-to-flash will soon be way more common than
    >> frontswap, it needs to be solved (either in flash or in the swap code).
    > While I admit that I started this whole discussion by implying
    > that frontswap (and cleancache) might be useful for SSDs, I think
    > we are going far astray here. Frontswap is synchronous for a
    > reason: It uses real RAM, but RAM that is not directly addressable
    > by a (guest) kernel. SSD's (at least today) are still I/O devices;
    > even though they may be very fast, they still live on a PCI (or
    > slower) bus and use DMA. Frontswap is not intended for use with
    > I/O devices.
    > Today's memory technologies are either RAM that can be addressed
    > by the kernel, or I/O devices that sit on an I/O bus. The
    > exotic memories that I am referring to may be a hybrid:
    > memory that is fast enough to live on a QPI/hypertransport,
    > but slow enough that you wouldn't want to randomly mix and
    > hand out to userland apps some pages from "exotic RAM" and some
    > pages from "normal RAM". Such memory makes no sense today
    > because OS's wouldn't know what to do with it. But it MAY
    > make sense with frontswap (and cleancache).
    > Nevertheless, frontswap works great today with a bare-metal
    > hypervisor. I think it stands on its own merits, regardless
    > of one's vision of future SSD/memory technologies.

    Even when frontswapping to RAM on a bare metal hypervisor it makes sense
    to use an async API, in case you have a DMA engine on board.

    error compiling committee.c: too many arguments to function

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