[ovirt-users] Free Memory In Hosts

[Dan Kenigsberg]

On Wed, Sep 10, 2014 at 11:57:05PM +0300, Mohyedeen Nazzal wrote:
> Hi All,
> I have noticed that there is a huge difference between memory reading
> obtained from top or free commands, and values displayed on ovirt engine.
> "Host "
> 
> Example:
> Engine Version : *ovirt-engine-3.4.3-1.el6.noarch*
> *OS: Centos 6.5_x86_64*
> 
> *Used Memory:*
> *from free:*
> [root at oVirt ~]# free
>                       total       used       free     shared    buffers
> cached
> Mem:      65890412   65609864     280548          0     305408   53759412
> 
> from Egnine Webpage:
> 
> only 12G is being used.
> 
> Is there an explanation for this ?

It's a Linux thing. When a file is opened, it is mapped into memory, but
when it is closed Linux does not evict it before memory is released
again. Thus, a long-running active host reaches 0 free mem sooner than
later.

For oVirt GUI, we found this misleading - there, "free" means "how much
memory is available for new VMs to use". Therefore oVirt reports
"buffred" and "cached" memory as free, too.