Messages in this thread | | | Date | Wed, 2 Nov 2005 13:00:48 +0100 | From | Ingo Molnar <> | Subject | Re: [Lhms-devel] [PATCH 0/7] Fragmentation Avoidance V19 |
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* 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).]
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