mirror of
https://github.com/cloud-hypervisor/cloud-hypervisor.git
synced 2024-11-05 03:21:13 +00:00
77 lines
2.1 KiB
Markdown
77 lines
2.1 KiB
Markdown
|
# Balloon
|
||
|
|
|
||
|
|
Cloud Hypervisor implements a balloon device based on the VIRTIO specification.
|
||
|
|
Its main purpose is to provide the host a way to reclaim memory by controlling
|
||
|
|
the amount of memory visible to the guest. But it also provides some interesting
|
||
|
|
features related to guest memory management.
|
||
|
|
|
||
|
|
## Parameters
|
||
|
|
|
||
|
|
`BalloonConfig` (known as `--balloon` from the CLI perspective) contains the
|
||
|
|
list of parameters available for the balloon device.
|
||
|
|
|
||
|
|
```rust
|
||
|
|
struct BalloonConfig {
|
||
|
|
pub size: u64,
|
||
|
|
pub deflate_on_oom: bool,
|
||
|
|
pub free_page_reporting: bool,
|
||
|
|
}
|
||
|
|
```
|
||
|
|
|
||
|
|
```
|
||
|
|
--balloon <balloon> Balloon parameters "size=<balloon_size>,deflate_on_oom=on|off,free_page_reporting=on|off"
|
||
|
|
```
|
||
|
|
|
||
|
|
### `size`
|
||
|
|
|
||
|
|
Size of the balloon device. It is subtracted from the VM's total size. For
|
||
|
|
instance, if creating a VM with 4GiB of RAM, along with a balloon of 1GiB, the
|
||
|
|
guest will be able to use 3GiB of accessible memory. The guest sees all the RAM
|
||
|
|
and unless it is balloon enlightened is entitled to all of it.
|
||
|
|
|
||
|
|
This parameter is mandatory.
|
||
|
|
|
||
|
|
Value is an unsigned integer of 64 bits corresponding to the balloon size in
|
||
|
|
bytes.
|
||
|
|
|
||
|
|
_Example_
|
||
|
|
|
||
|
|
```
|
||
|
|
--balloon size=1G
|
||
|
|
```
|
||
|
|
|
||
|
|
### `deflate_on_oom`
|
||
|
|
|
||
|
|
Allow the guest to deflate the balloon if running Out Of Memory (OOM). Assuming
|
||
|
|
the balloon size is greater than 0, this means the guest is allowed to reduce
|
||
|
|
the balloon size all the way down to 0 if this can help recover from the OOM
|
||
|
|
event.
|
||
|
|
|
||
|
|
This parameter is optional.
|
||
|
|
|
||
|
|
Value is a boolean set to `off` by default.
|
||
|
|
|
||
|
|
_Example_
|
||
|
|
|
||
|
|
```
|
||
|
|
--ballloon size=2G,deflate_on_oom=on
|
||
|
|
```
|
||
|
|
|
||
|
|
### `free_page_reporting`
|
||
|
|
|
||
|
|
Allow the guest to report lists of free pages. This feature doesn't require the
|
||
|
|
balloon to be of any specific size as it doesn't impact the balloon size. The
|
||
|
|
guest can let the VMM know about pages that are free after they have been used.
|
||
|
|
Based on this information, the VMM can advise the host that it doesn't need
|
||
|
|
these pages anymore.
|
||
|
|
|
||
|
|
This parameter is optional.
|
||
|
|
|
||
|
|
Value is a boolean set to `off` by default.
|
||
|
|
|
||
|
|
_Example_
|
||
|
|
|
||
|
|
```
|
||
|
|
--ballloon size=0,free_page_reporting=on
|
||
|
|
```
|