[Users] Ovirt Memory Page Sharing or to less memory

[Mathok]

2012/10/17 Alan Johnson <alan at datdec.com>

> On Wed, Oct 17, 2012 at 5:02 PM, Mathok <mathok1 at googlemail.com> wrote:
>
>> Same here with ovirt 3.1.0-2 i can't see a change in the UI. But i'm able
>> to start more VMs and hava a higher usag of my swap partiotion so i think
>> the change had the desired effect
>>
>
> Oh, does this take advantage of host swap space as well?  I thought I had
> read oVirt could do that somewhere, but I have been reading about so many
> different virtualization systems over the last few months that when the RHEV
> 3.1 Admin Guide<https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enterprise_Virtualization/3.1-Beta/html-single/Administration_Guide/index.html>did not mention swap space in section "4.2.2.2. Memory Optimization
> Settings Explained", I was not sure if it applied here.  This is all it
> says at the moment:
>
> "Memory page sharing allows virtual machines to use up to 200% of their
> allocated memory by utilizing unused memory in other virtual machines. This
> process is based on the assumption that the virtual machines in your Red
> Hat Enterprise Virtualization environment will not all be running at full
> capacity at the same time, allowing unused memory to be temporarily
> allocated to a particular virtual machine."
>
>
> Do you have a reference handy that confirms and explains this?  I put some
> speedy SSDs in my hosts to hopefully take advantage of this (and maybe run
> gluster), so I am hoping to see that in print somewhere.  I'll dig it up if
> you don't have it handy, but a confirmation that this is
> your experience and understanding would make me feel better in the mean
> time.
>

let me explain my (now fixed) problem i have a ovirt host with 8 GB Ram and
12 VMs every with 256 MB Physical Memory Guarantee. When i start my two
mysql-cluster vms they will use the 256 PMG plus 3,75 GB MS they have
defined a max of 4 GB MS. At this poitn now the problem begins the mysql
taken the hole memory in both vms and now there is no more free ram at the
host and it is not possible to start more vms.

(this is also speculation im not a expert) So i need for my understanding a
higher rate of memory overcommit to be able to start all vms, and for that
the host must use the swap to have enough memory for overcomit to start all
vms and yes the higher the rate, the worse the performance. I'm not sure if
this is the right or good way tho fix this problem

(sorry for my bad english I hope this is understandable)
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