Re: [Xen-devel] RE: tmem - really default to on?

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> Tim Deegan <Tim.Deegan@xxxxxxxxxx> 09.02.10 11:45 >>>
>At 17:18 +0000 on 08 Feb (1265649531), Dan Magenheimer wrote:
>> The order=2 shadow page allocation should also probably be
>> considered a "bug" for post-4.0 as, I think, even ballooning
>> will eventually fragment memory and theoretically 75% of
>> physical memory might be unused and domain creation (or PV
>> migration) will fail.
>
>I think the correct approach to all of this is to move system-wide to
>allocating memory in 2MB contiguous aligned chunks.  There's no sense in
>doing guest allocations any finer-grained than that and there are
>noticeable performance wins from all the superpage support that's gone
>in recently.  Then little things like needing 16k contiguous areas just
>go away.

I have to admit that I can't see how this would work with ballooning,
or (if the balloon driver was adjusted to deal with this) with
fragmentation inside Dom0 (or any other guest that memory is
intended to be removed from). Nor am I sure tmem could be
changed to deal with 2Mb chunks instead of 4k ones.

Jan


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