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We are reserving 2 CPU and 16G RAM for the hypervisor. I haven't seen any OOM errors. Where should I look for those?

-----Original Message-----
From: Sean Mooney <smooney at redhat.com> 
Sent: Monday, February 3, 2020 2:47 PM
To: Albert Braden <albertb at synopsys.com>; OpenStack Discuss ML <openstack-discuss at lists.openstack.org>
Subject: Re: Virtio memory balloon driver

On Mon, 2020-02-03 at 21:36 +0000, Albert Braden wrote:
> When we build a Centos 7 VM with 1.4T RAM it fails with "[   17.797177] BUG: unable to handle kernel paging request at
> ffff988b19478000"
> 
> I asked in #centos and they asked me to show a list of devices from a working VM (if I use 720G RAM it works). This is
> the list:
> 
> [root at alberttest1 ~]# lspci
> 00:00.0 Host bridge: Intel Corporation 440FX - 82441FX PMC [Natoma] (rev 02)
> 00:01.0 ISA bridge: Intel Corporation 82371SB PIIX3 ISA [Natoma/Triton II]
> 00:01.1 IDE interface: Intel Corporation 82371SB PIIX3 IDE [Natoma/Triton II]
> 00:01.2 USB controller: Intel Corporation 82371SB PIIX3 USB [Natoma/Triton II] (rev 01)
> 00:01.3 Bridge: Intel Corporation 82371AB/EB/MB PIIX4 ACPI (rev 03)
> 00:02.0 VGA compatible controller: Cirrus Logic GD 5446
> 00:03.0 Ethernet controller: Red Hat, Inc. Virtio network device
> 00:04.0 SCSI storage controller: Red Hat, Inc. Virtio block device
> 00:05.0 SCSI storage controller: Red Hat, Inc. Virtio block device
> 00:06.0 SCSI storage controller: Red Hat, Inc. Virtio block device
> 00:07.0 Unclassified device [00ff]: Red Hat, Inc. Virtio memory balloon
> [root at alberttest1 ~]# lsusb
> Bus 001 Device 002: ID 0627:0001 Adomax Technology Co., Ltd
> Bus 001 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
> 
> They suspect that the "Virtio memory balloon" driver is causing the problem, and that we should disable it. I googled
> around and found this:
> 
> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.linux-2Dkvm.org_page_Projects_auto-2Dballooning&d=DwICaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=XrJBXYlVPpvOXkMqGPz6KucRW_ils95ZMrEmlTflPm8&m=iMCOz64cWwXgiqbpObDBdGZPUoLuQp4G931VKc_hqxI&s=uEnvgAhTPKxJpvz6a3bQisI9406ul8Q2SSHDCV1lqvU&e= 
> 
> It looks like memory ballooning is deprecated. How can I get rid of the driver?
https://urldefense.proofpoint.com/v2/url?u=http-3A__www.linux-2Dkvm.org_page_Projects_auto-2Dballooning&d=DwICaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=XrJBXYlVPpvOXkMqGPz6KucRW_ils95ZMrEmlTflPm8&m=iMCOz64cWwXgiqbpObDBdGZPUoLuQp4G931VKc_hqxI&s=uEnvgAhTPKxJpvz6a3bQisI9406ul8Q2SSHDCV1lqvU&e= 
states that no qemu that exists today implements that feature but the fact you see it in lspci
seams to be in conflict with that. there are several refernce to the feature in later release of qemu
and it is documented in libvirt https://urldefense.proofpoint.com/v2/url?u=https-3A__libvirt.org_formatdomain.html-23elementsMemBalloon&d=DwICaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=XrJBXYlVPpvOXkMqGPz6KucRW_ils95ZMrEmlTflPm8&m=iMCOz64cWwXgiqbpObDBdGZPUoLuQp4G931VKc_hqxI&s=DSej4fERS8HGIYb7CaIkbVBpssWtSxCbBRxukkAH0rI&e= 

there is no way to turn it off specificly currently and im not aware of it being deprecated.
the guest will not interact witht he vitio memory balloon by default.
it is there too allow the guest to free memory and retrun it to the host to allow
copperation between the guests and host to enable memory oversubscription.
i belive this normally need the qemu guest agent to be deploy to work fully.

with a 1.4TB vm how much memory have you reserved on the host.
qemu will need memory to implement the vm emulation and this tends to increase as the guess
uses more resouces.

my first incliantion would be to check it the vm was killed as a result of a OOM event on the host.