Re: [ovirt-users] Using zRam with oVirt Nodes

[Fernando Frediani]

All nodes I user zSwap (or Swap in zRam) I do have also some swap space 
in disk with lower priority which when/if gets used means something warning.


Overall the usage of zSwap helps a lot to increase the density of a Host 
at the cost of CPU which in most cases is more idle than memory or storage


Fernando


On 30/12/2016 21:47, Pavel Gashev wrote:

I enable zSwap on my oVirt nodes by default. However zSwap is not the same 
thing as zRam. The purpose of zSwap is decreasing I/O by compressing swap 
itself. zSwap uses some ram for compressed swap, but it doesn’t try to keep a 
page in memory if it can’t be compressed.

I find using of zRam without swap too risky. You don’t know when OOM killer 
start its job.

-Original Message-
From:  on behalf of Fernando Frediani 

Date: Friday 30 December 2016 at 20:06
To: "users@ovirt.org" 
Subject: [ovirt-users] Using zRam with oVirt Nodes

Hello folks.

On simple libvirt/KVM hosts in order to improve RAM usage and avoid swap
to disk I use zRam with swap to RAM technique. So create half of amount
of host memory in zRam disk divided by the number of CPU cores. Works
pretty well.

Has anyone tried it with oVirt Nodes or even has it been considered as a
feature to simply turn on/off ?

Thanks
Fernando

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Re: [ovirt-users] Using zRam with oVirt Nodes

[Pavel Gashev]

I enable zSwap on my oVirt nodes by default. However zSwap is not the same 
thing as zRam. The purpose of zSwap is decreasing I/O by compressing swap 
itself. zSwap uses some ram for compressed swap, but it doesn’t try to keep a 
page in memory if it can’t be compressed. 

I find using of zRam without swap too risky. You don’t know when OOM killer 
start its job.

-Original Message-
From:  on behalf of Fernando Frediani 

Date: Friday 30 December 2016 at 20:06
To: "users@ovirt.org" 
Subject: [ovirt-users] Using zRam with oVirt Nodes

Hello folks.

On simple libvirt/KVM hosts in order to improve RAM usage and avoid swap 
to disk I use zRam with swap to RAM technique. So create half of amount 
of host memory in zRam disk divided by the number of CPU cores. Works 
pretty well.

Has anyone tried it with oVirt Nodes or even has it been considered as a 
feature to simply turn on/off ?

Thanks
Fernando

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Re: [ovirt-users] Using zRam with oVirt Nodes

[Fernando Frediani]

Hello it's the same thing zswap.

The use case is to be able to put more stuff in a single host without it 
need needing to swap to slow disks. You sacrifice CPU and avoid a lot 
slower swap to disk.


Fernando

On 30/12/2016 16:41, Yaniv Kaul wrote:



On Dec 30, 2016 7:06 PM, "Fernando Frediani" 
> 
wrote:


Hello folks.

On simple libvirt/KVM hosts in order to improve RAM usage and
avoid swap to disk I use zRam with swap to RAM technique. So
create half of amount of host memory in zRam disk divided by the
number of CPU cores. Works pretty well.

Has anyone tried it with oVirt Nodes or even has it been
considered as a feature to simply turn on/off ?


What exactly is the use case?
I'd use zram for temporary disks, using the VDSM hook for them.
I think you are referring to zswap?
Y.


Thanks
Fernando

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Re: [ovirt-users] Using zRam with oVirt Nodes

[Yaniv Kaul]

On Dec 30, 2016 7:06 PM, "Fernando Frediani" 
wrote:

Hello folks.

On simple libvirt/KVM hosts in order to improve RAM usage and avoid swap to
disk I use zRam with swap to RAM technique. So create half of amount of
host memory in zRam disk divided by the number of CPU cores. Works pretty
well.

Has anyone tried it with oVirt Nodes or even has it been considered as a
feature to simply turn on/off ?


What exactly is the use case?
I'd use zram for temporary disks, using the VDSM hook for them.
I think you are referring to zswap?
Y.


Thanks
Fernando

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