Re: [Xen-devel] suggested domain0 memory size

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

> >>Hi,
> >>what is minimal recommended memory reservation for domain0? It won't run 
> >>any services apart from sshd and xend and will provide files from /home 
> >>(ext3) to other domains as their block devices. Machine is 466MHz 
> >>Celeron with 256MB of RAM, UDMA/33 IDE interface, and will run about 5 
> >>other domains, so less is more ;-).
> > 
> > 
> > Boot it with 64MB and then use the balloon driver to crank it
> > down a bit. Give it a swap file to be on the safe side.
> 
> Just a small question - if I use `xm balloon Domain-0 64`, `xm info` 
> reports correct amount of memory as free, but `free` says that domain0 
> has still $original_memory_size total, but used memory grows up, is it 
> correct?

>From the point of view of the kernel, ballooned memory is actually "in
use". This is because the balloon is inflated by requesting memory
from the kernel allocator -- the kernel assumes this memory is in use
by the balloon driver, when in fact it is returned to Xen.

So, 'free' and 'cat /proc/meminfo' will both mislead you. You need to
subtract the balloon size from the 'total memory' field to find out
how much memory is *really* in use by the domain.

 -- Keir

> (total, used, free, shared, buffers, cached)
> # free | grep Mem
> Mem:        116692      29056      87636          0        460       9600
> # xm info | grep memory
> memory                 : 255
> free_memory            : 126
> # xm balloon Domain-0 64
> # free | grep Mem
> Mem:        116692      83536      33156          0        460       9600
> # xm info | grep memory
> memory                 : 255
> free_memory            : 179
> 
> TIA,
> j.
> 
> 
> 
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