[ovirt-users] Free Memory In Hosts

[Martin Sivak]

Hi,

If you look at the full free output you will see another line:

             total       used       free     shared    buffers     cached
Mem:       8057004    7491980     565024          0     234592    2005452
-/+ buffers/cache:    5251936    2805068

The +/- buffers/cache tells you how much memory you will have available after you (the kernel) clean all buffers and caches.

And that is the number we look at.

--
Martin Sivák
msivak at redhat.com
Red Hat Czech
RHEV-M SLA / Brno, CZ

----- Original Message -----
> 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.
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