From: Friedrich Weber <f.weber@proxmox.com>
To: Fiona Ebner <f.ebner@proxmox.com>,
Proxmox VE development discussion <pve-devel@lists.proxmox.com>
Subject: Re: [pve-devel] [PATCH docs 1/2] pci passthrough: mention incompatibility with ballooning
Date: Tue, 14 Nov 2023 11:20:40 +0100 [thread overview]
Message-ID: <7b260560-7394-4908-bd85-42f0c6f517d2@proxmox.com> (raw)
In-Reply-To: <39993056-a0d8-418b-8abd-71df1b86be99@proxmox.com>
On 14/11/2023 09:30, Fiona Ebner wrote:
> Am 13.11.23 um 18:09 schrieb Friedrich Weber:
>>
>> +xref:qm_ballooning[Automatic memory allocation (ballooning)] is not possible
>> +when using PCI(e) passthrough. As the PCI device may use DMA (Direct Memory
>> +Access), QEMU needs to map the complete guest memory on VM startup. Hence, the
>> +QEMU process will use at least the (maximum) configured amount of VM memory and
>> +setting a minimum amount does not have any effect. When using PCI(e)
>> +passthrough, it is recommended to set memory and minimum memory to the same
>> +amount and keep the balloning device enabled. However, keep in mind that the
>
> typo: s/balloning/ballooning/
Oops, thanks.
> Is there any advantage to keeping the ballooning device enabled?
>
>> +memory consumption reported in the GUI for the VM may be much lower than the
>> +memory consumption of the QEMU process.
>
> Maybe mention what the reported value is?
In my understanding: If the ballooning device is enabled (and a balloon
driver present in the guest), the VM memory usage numbers are taken as
reported by the balloon driver [1] (I'd say "as seen from within the
guest"?). If the ballooning device is disabled, they are inferred from
the rss and vsize of the QEMU process [2], so I'd say "as seen from the
host".
I guess in the end the user has to decide which perspective they care
about? I'll try to make this clearer in the v2.
[1]
https://git.proxmox.com/?p=qemu-server.git;a=blob;f=PVE/QemuServer.pm;h=c465fb6f64ae30dec5112fc4439f9181c2eba4e9;hb=feb51881d#l3013
[2]
https://git.proxmox.com/?p=qemu-server.git;a=blob;f=PVE/QemuServer.pm;h=c465fb6f64ae30dec5112fc4439f9181c2eba4e9;hb=feb51881d#l2967
next prev parent reply other threads:[~2023-11-14 10:20 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-13 17:09 [pve-devel] [PATCH docs/qemu-server 0/2] Ballooning/PCI passthrough incompatibility: add warning and docs Friedrich Weber
2023-11-13 17:09 ` [pve-devel] [PATCH docs 1/2] pci passthrough: mention incompatibility with ballooning Friedrich Weber
2023-11-14 8:30 ` Fiona Ebner
2023-11-14 10:20 ` Friedrich Weber [this message]
2023-11-17 12:37 ` Friedrich Weber
2023-11-13 17:09 ` [pve-devel] [PATCH qemu-server 2/2] vm start: warn if using ballooning and PCI(e) passthrough Friedrich Weber
2023-11-14 9:13 ` Fiona Ebner
2023-11-14 10:20 ` Friedrich Weber
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