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

[Ingo Molnar]

* Gerrit Huizenga <gh@xxxxxxxxxx> 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
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