Re: [Xen-devel] [PATCH] linux/balloon:don't allow ballooningdowna domain below a reasonable limit

[Goswin von Brederlow <goswin-v-b@xxxxxx>]

"Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> writes:

>> >OK, I think I am understanding it a bit better:
>> >the max_pfn part is just adding in some "slop"
>> >which is a fraction of total main memory which
>> >is growing smaller (roughly logarithmically)
>> >as memory grows larger.  I'm still not sure about
>> >the magic values in MB2PAGES though... I'm guessing
>> >these were gathered somehow experimentally?
>> 
>> I have to defer to the original author here - Kurt?
>
> Eagerly awaiting... In addition to cutting it
> in half, I subtracted another 10MB (in a memory=512
> domain) and still didn't see any OOMs, though my
> testing was admittedly limited.
>  
>> >With the "divide result of your algorithm by two",
>> >I was able to get thirteen 512MB domains (idle
>> >for now) running on a 2GB system.
>> 
>> You mean ballooned-down domains, right? Perhaps using your
>> self-ballooning change? I have to admit I'm a little nervous
>> about attempting to overcommit memory in this way in a
>> production environment, but as long as this depends on a
>> decision of the operator it's certainly a good option to have.
>
> Yes, ballooned-down domains.  In fact with minimum_target()
> modified as above (half of algorithm minus 10MB) and
> a variable load (repeating { compile xen; sleep(30<rand<541) }),
> I got fifteen 512MB domains running on a 2GB systems.
>
> Agreed that there are many environments where this kind
> of ballooning would cause performance problems (or worse).
> However, there are certainly some environments (and some
> competitive situations ;-) where one might choose to
> tradeoff performance to run more VMs per physical machine.
>
> Dan

I for example have 6 domains to compile software for 32bit and 64bit
for Debian stable, testing and unstable each. They can benefit from
more memory when they build gcc for example. But 99.9% of the time
they just wait for something to do.

It would be real nice to autoballoon them down when idle. In fact I
would like to auto balloon them so that the domain that swaps least
gets sized down and the domain that swaps most gets the pages. To a
lesser degree cpu and IO usage should also play a part.

MfG
        Goswin

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