Re: [Xen-devel] [PATCH v3] libxl: Wait for ballooning if free memory is increasing

[Mike Latimer <mlatimer@xxxxxxxx>]

Hi Wei,

On Friday, February 13, 2015 11:01:41 AM Wei Liu wrote:
> On Tue, Feb 10, 2015 at 09:17:23PM -0700, Mike Latimer wrote:
> > Prior to my changes, this issue would only be noticed when starting very
> > large domains - due to the loop being limited to 3 iterations. (For
> > example, when ballooning 512G, dom0 memory could be reduced up to 1.5T.)
> > With my changes, this loop can take several more iterations (10 or many
> > more in testing). With each iteration lowering dom0's target, the end
> > result can be dom0 ballooning down 100's of gigabytes, just to satisfy a
> > much smaller request. (On one machine, a 64G guest can result in dom0
> > ballooning down 500G.)
> 
> I'm curious why freemem doesn't not return when dom0 is ballooned down 64G?
> I.e. I think libxl_wait_for_free_memory should return 0 in that case and
> freeme should just return. Does it suggest there are other domains
> competing for free memory and dom0 is doing the right thing?

I was only testing with a single domain. freemem returns 0 until freemem-slack 
is free, then the difference between freemem and freemem-slack is returned.

However, there are actually a couple of different problems here - and the whole 
situation is closely related to freemem_slack. As the patch submitted with 
this thread is only a victim here, maybe it's best to move the discussion over 
to the freemem-slack thread. I'll reply in detail there.

Thanks!
Mike

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