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    SubjectRe: [Lhms-devel] [PATCH 0/7] Fragmentation Avoidance V19

    * Gerrit Huizenga <gh@us.ibm.com> wrote:

    >
    > On Wed, 02 Nov 2005 11:41:31 +0100, Ingo Molnar wrote:
    > >
    > > * Gerrit Huizenga <gh@us.ibm.com> wrote:
    > >
    > > > > generic unpluggable kernel RAM _will not work_.
    > > >
    > > > Actually, it will. Well, depending on terminology.
    > >
    > > 'generic unpluggable kernel RAM' means what it says: any RAM seen by the
    > > kernel can be unplugged, always. (as long as the unplug request is
    > > reasonable and there is enough free space to migrate in-use pages to).
    >
    > Okay, I understand your terminology. Yes, I can not point to any
    > particular piece of memory and say "I want *that* one" and have that
    > request succeed. However, I can say "find me 50 chunks of memory
    > of your choosing" and have a very good chance of finding enough
    > memory to satisfy my request.

    but that's obviously not 'generic unpluggable kernel RAM'. It's very
    special RAM: RAM that is free or easily freeable. I never argued that
    such RAM is not returnable to the hypervisor.

    > > reliable unmapping of "generic kernel RAM" is not possible even in a
    > > virtualized environment. Think of the 'live pointers' problem i outlined
    > > in an earlier mail in this thread today.
    >
    > Yeah - and that isn't what is being proposed here. The goal is to
    > ask the kernel to identify some memory which can be legitimately
    > freed and hasten the freeing of that memory.

    but that's very easy to identify: check the free list or the clean
    list(s). No defragmentation necessary. [unless the unit of RAM mapping
    between hypervisor and guest is too coarse (i.e. not 4K pages).]

    Ingo
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