[Xen-users] Re: Memory resizing

[Anthony Liguori <aliguori@xxxxxxxxxx>]

Ballooning down to 160MB is not quite the same as creating a domain with 
160MB.
What's really going on here, is that you create a domain with 7800MB, 
and then the balloon driver tells the kernel that it's allocated 
(7800-160)MBs.  The kernel really doesn't know that the balloon driver 
gave that memory back to Xen--it just thinks it's a greedy kernel module.
At any rate, Linux tends to allocate certain structures as percentages. 
 Furthermore, the swapping heuristics are going to be based on the 
assumption that the system really has 7800MB of memory.  Since you only 
have a 1G swap, I imagine it will be very conservative about how it uses 
that swap.
Regards,

Anthony Liguori

Jiri Denemark wrote:
> Hi.
>
> I have a machine with 8GB of memory and I'd like to create two domUs in such a
> way that each domain can use memory from about 160MB to 7800MB (set manually
> using xm mem-set).
>
> First, I create Domain-1 with memory=7800, than reduce its current memory
> allocation to 160MB by xm mem-set 1 160. After that, the second domU is
> started in the same way. Up to now, everything is ok.
>
> After logging in the first domain, free tells me there is 62MB of free memory
> out of total 160MB and 1GB of free swap. Then I start a process which consumes
> more than 62 megabytes of memory (to be specific, view a 100+MB file with the
> vim). After a while, the process is killed by OOM killer, even though there is
> plenty of space available in swap. When I create the domain with memory=160,
> everything works as expected, free space in swap is used and no process is
> killed by OOM.
>
> Do you have any idea where the problem could be?
>
> Thanks a lot.
>
> Jirka

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