Re: [Xen-devel] Proposed new "memory capacity claim" hypercall/feature

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 30.10.12 at 00:21, Dan Magenheimer <dan.magenheimer@xxxxxxxxxx> wrote:
>>  From: Tim Deegan [mailto:tim@xxxxxxx]
>> As I said, I'm not opposed to this, though even after reading through
>> the other thread I'm not convinced that it's necessary (except in cases
>> where guest-controlled operations are allowed to consume unbounded
>> memory, which frankly gives me the heebie-jeebies).
> 
> A really detailed discussion of tmem would probably be good but,
> yes, with tmem, guest-controlled* operations can and frequently will
> absorb ALL physical RAM.  However, this is "freeable" (ephemeral)
> memory used by the hypervisor on behalf of domains, not domain-owned
> memory.
> 
> * "guest-controlled" I suspect is the heebie-jeebie word... in
>   tmem, a better description might be "guest-controls-which-data-
>   and-hypervisor-controls-how-many-pages"

But isn't tmem use supposed to be transparent in this respect, i.e.
if a "normal" allocation cannot be satisfied, tmem would jump in
and free sufficient space? In which case there's no need to do
any accounting outside of the control tools (leaving aside the
smaller hypervisor internal allocations, which the tool stack needs
to provide room for anyway).

Jan


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