Re: [Xen-devel] domain creation vs querying free memory (xend and xl)

[Tim Deegan <tim@xxxxxxx>]

At 13:03 -0700 on 01 Oct (1349096617), Dan Magenheimer wrote:
> Bearing in mind that I know almost nothing about xl or
> the tools layer, and that, as a result, I tend to look
> for hypervisor solutions, I'm thinking it's not possible to
> solve this without direct participation of the hypervisor anyway,
> at least while ensuring the solution will successfully
> work with any memory technology that involves ballooning
> with the possibility of overcommit (i.e. tmem, page sharing
> and host-swapping, manual ballooning, PoD)...  EVEN if the
> toolset is single threaded (i.e. only one domain may
> be created at a time, such as xapi). [1]

TTBOMK, Xapi actually _has_ solved this problem, even with ballooning
and PoD.  I don't know if they have any plans to support sharing,
swapping or tmem, though.

Adding a 'reservation' of free pages that may only be allocated by a
given domain should be straightforward enough, but I'm not sure it helps
much.  In the 'balloon-to-fit' model where all memory is already
allocated to some domain (or tmem), some part of the toolstack needs to
sort out freeing up the memory before allocating it to another VM.
Surely that component needs to handle the exclusion too - otherwise a
series of small VM creations could stall a large one indefinitely.

Cheers,

Tim.

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