Re: performance tuning, problem with paravirtualized clock

Anthony Liguori
2008-04-06T22:33:23Z

Nikola Ciprich wrote:
> Anthony Liguori wrote:
>> You won't see a gain with tmpfs. Make sure you reserve huge pages
>> first. For a 1GB guest, you'll need something like:
>>
>> echo 540 > /proc/sys/vm/nr_hugepages
>>
>> When you create a VM, you need a bit more memory than 1GB for
>> per-guest overhead. That's why I reserve 540 instead of 512. You
>> can probably get away with 530 really.
>>
>> Check that it succeeded by cat'ing /proc/meminfo.
>>
> Well, I tried various values now, and booting fails immediately:
> Decompressing Linux...

It's very likely that you won't be able to allocate enough pages to run
a guest if your system has been running sufficient long and memory is
highly fragmented.

If you cat /proc/meminfo and HugePages_Free is much less than 540,
you're not going to be able to create a 1GB guest. Unfortunately, you
won't get a failure until the guest tries to use memory.

The only solution is to reboot and reserve huge pages early before they
get fragmented.

Regards,

Anthony Liguori

> invalid compressed format (err=1)
>
> -- System halted
>
>
> weird...
> anyways I'll also give fresh kvm-65 a try now :)