Re: [Xen-users] Limits on memory which can be set using xm mem-set

[Jiri Denemark <jirka@xxxxxxxxxxx>]

Hi Mark,

Thanks for your reply.

> I've not heard of this behaviour in ballooning before, although to be honest 
> I'd expect such an aggressive shrinking might upset the guest anyhow, so it's 
> not necessarily something you'd want to do in production!
Well, of course, the guest gets upset if its memory is shrank too much. And
the lowest amount of memory is related to the maximum memory a domain was
started with. However, 160MB is quite fine for a guest originally started with
3.5GB but only if only few daemons are running in it. For example, for a
domain with 15GB, it seems the minimum is somewhere around 500MB.

> echo size_in_bytes > /proc/xen/balloon
This really helped much. I tried it and realized that I couldn't shrink the
memory below 400MB. So the balloon driver was the culprit. I looked into it
and found minimum_target() function, which counts minimum memory based on
domain's maximum memory. However, it's worth noting that the kernel is 2.6.21
by SuSE and there is no such function in 2.6.18 kernel from Xen 3.2.0
distribution. So the problem is only related to SuSE kernels.

Jirka

-- 
Theorem: a cat has nine tails.
Proof:
    No cat has eight tails. A cat has one tail more than no cat.
    Therefore, a cat has nine tails.

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