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

Ingo Molnar
2005-11-02T10:41:31Z

* 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).

> There are two usage models here - those which intend to remove
> physical elements and those where the kernel returnss management of
> its virtualized "physical" memory to a hypervisor. In the latter
> case, a hypervisor already maintains a virtual map of the memory and
> the OS needs to release virtualized "physical" memory. I think you
> are referring to RAM here as the physical component; however these
> same defrag patches help where a hypervisor is maintaining the real
> physical memory below the operating system and the OS is managing a
> virtualized "physical" memory.

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.

Ingo