kata-containers/cloud-hypervisor
1
0
Fork 0
mirror of https://github.com/cloud-hypervisor/cloud-hypervisor.git synced 2026-08-05 02:19:16 +00:00
Code Issues Packages Projects Releases Wiki Activity

vmm: add per-zone mergeable option to --memory-zone

Browse Source 
Add a `mergeable` field to `MemoryZoneConfig` so that KSM page merging
can be enabled selectively per memory zone rather than globally for all
guest RAM.

Previously, `MADV_MERGEABLE` was only controllable via the top-level
`--memory mergeable=on` flag, which applied uniformly to all regions.
With this change, users can leave boot memory unmerged while enabling
KSM only on hotplug zones:

  --memory size=0,hotplug_method=virtio-mem
  --memory-zone id=boot,size=512M,shared=on,mergeable=off
  --memory-zone id=hotplug,size=256M,hotplug_size=1G,shared=off,mergeable=on

The `MemoryZone` runtime struct now carries the `mergeable` flag so
that both `allocate_address_space` and `add_ram_region` can apply
per-zone `MADV_MERGEABLE` instead of the global `self.mergeable`.
The top-level `--memory mergeable=on` path continues to work unchanged:
the default zone is synthesised from `MemoryConfig` and inherits its
`mergeable` value.

AI/LLM disclosure: this patch was co-authored with
GitHub Copilot and Claude Code (Opus 4.6).

Signed-off-by: JP Kobryn <inwardvessel@gmail.com>
This commit is contained in:
JP Kobryn
2026-04-08 18:52:01 -07:00
committed by Rob Bradford
parent 3a23e2f841
commit bdc7a6947d
4 changed files with 145 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files

31
docs/memory.md
View File

@@ -214,11 +214,12 @@ struct MemoryZoneConfig {
hotplug_size: Option<u64>,
hotplugged_size: Option<u64>,
prefault: bool,
mergeable: bool,
}
```
```
--memory-zone <memory-zone> User defined memory zone parameters "size=<guest_memory_region_size>,file=<backing_file>,shared=on|off,hugepages=on|off,hugepage_size=<hugepage_size>,host_numa_node=<node_id>,id=<zone_identifier>,hotplug_size=<hotpluggable_memory_size>,hotplugged_size=<hotplugged_memory_size>,prefault=on|off"
--memory-zone <memory-zone> User defined memory zone parameters "size=<guest_memory_region_size>,file=<backing_file>,shared=on|off,hugepages=on|off,hugepage_size=<hugepage_size>,host_numa_node=<node_id>,id=<zone_identifier>,hotplug_size=<hotpluggable_memory_size>,hotplugged_size=<hotplugged_memory_size>,prefault=on|off,mergeable=on|off"
```
This parameter expects one or more occurrences, allowing for a list of memory
@@ -422,6 +423,34 @@ _Example_
--memory-zone id=mem0,size=1G,prefault=on
```
### `mergeable`
Specifies if the pages from this memory zone must be marked as _mergeable_,
enabling Kernel Same-page Merging (KSM) for this zone.
This is the per-zone equivalent of the top-level `--memory mergeable=on` option.
It allows KSM to be enabled selectively — for example, enabling it only on a
hotplug zone while leaving boot memory unaffected:
```
--memory size=2G,mergeable=off
--memory-zone id=hotplug,size=0,hotplug_size=8G,mergeable=on
```
For KSM to have any effect, the host kernel must have KSM enabled:
```
echo 1 > /sys/kernel/mm/ksm/run
```
By default this option is turned off.
_Example_
```
--memory size=0
--memory-zone id=mem0,size=1G,mergeable=on
```
## NUMA settings
`NumaConfig` or what is known as `--numa` from the CLI perspective has been

90
vmm/src/config.rs
View File

@@ -1006,7 +1006,8 @@ impl MemoryConfig {
.add("host_numa_node")
.add("hotplug_size")
.add("hotplugged_size")
.add("prefault");
.add("prefault")
.add("mergeable");
parser.parse(memory_zone).map_err(Error::ParseMemoryZone)?;
let id = parser.get("id").ok_or(Error::ParseMemoryZoneIdMissing)?;
@@ -1047,6 +1048,11 @@ impl MemoryConfig {
.map_err(Error::ParseMemoryZone)?
.unwrap_or(Toggle(false))
.0;
let mergeable = parser
.convert::<Toggle>("mergeable")
.map_err(Error::ParseMemoryZone)?
.unwrap_or(Toggle(mergeable))
.0;
zones.push(MemoryZoneConfig {
id,
@@ -1059,6 +1065,7 @@ impl MemoryConfig {
hotplug_size,
hotplugged_size,
prefault,
mergeable,
});
}
Some(zones)
@@ -3750,6 +3757,87 @@ mod unit_tests {
Ok(())
}
#[test]
fn test_mem_zone_parsing() -> Result<()> {
// mergeable defaults to false
assert_eq!(
MemoryConfig::parse("size=0", Some(vec!["id=mem0,size=1G"]))?,
MemoryConfig {
size: 0,
zones: Some(vec![MemoryZoneConfig {
id: "mem0".to_string(),
size: 1 << 30,
..Default::default()
}]),
..Default::default()
}
);
// mergeable=on
assert_eq!(
MemoryConfig::parse("size=0", Some(vec!["id=mem0,size=1G,mergeable=on"]))?,
MemoryConfig {
size: 0,
zones: Some(vec![MemoryZoneConfig {
id: "mem0".to_string(),
size: 1 << 30,
mergeable: true,
..Default::default()
}]),
..Default::default()
}
);
// mergeable=off is explicit false
assert_eq!(
MemoryConfig::parse("size=0", Some(vec!["id=mem0,size=1G,mergeable=off"]))?,
MemoryConfig {
size: 0,
zones: Some(vec![MemoryZoneConfig {
id: "mem0".to_string(),
size: 1 << 30,
mergeable: false,
..Default::default()
}]),
..Default::default()
}
);
// per-zone mergeable independent of global mergeable
assert_eq!(
MemoryConfig::parse(
"size=1G,mergeable=off",
Some(vec!["id=hotplug,size=0,hotplug_size=4G,mergeable=on"])
)?,
MemoryConfig {
size: 1 << 30,
mergeable: false,
hotplug_method: HotplugMethod::Acpi,
zones: Some(vec![MemoryZoneConfig {
id: "hotplug".to_string(),
size: 0,
hotplug_size: Some(4 << 30),
mergeable: true,
..Default::default()
}]),
..Default::default()
}
);
// global mergeable=on inherited by zone with no explicit mergeable
assert_eq!(
MemoryConfig::parse("size=0,mergeable=on", Some(vec!["id=mem0,size=1G"]))?,
MemoryConfig {
size: 0,
mergeable: true,
zones: Some(vec![MemoryZoneConfig {
id: "mem0".to_string(),
size: 1 << 30,
mergeable: true,
..Default::default()
}]),
..Default::default()
}
);
Ok(())
}
#[test]
fn test_mem_parsing() -> Result<()> {
assert_eq!(MemoryConfig::parse("", None)?, MemoryConfig::default());

31
vmm/src/memory_manager.rs
View File

@@ -138,16 +138,18 @@ pub struct MemoryZone {
shared: bool,
hugepages: bool,
backing_page_size: u64,
mergeable: bool,
}
impl MemoryZone {
fn new(shared: bool, hugepages: bool, backing_page_size: u64) -> Self {
fn new(shared: bool, hugepages: bool, backing_page_size: u64, mergeable: bool) -> Self {
Self {
regions: Vec::new(),
virtio_mem_zone: None,
shared,
hugepages,
backing_page_size,
mergeable,
}
}
@@ -607,7 +609,7 @@ impl MemoryManager {
// Add zone id to the list of memory zones.
memory_zones.insert(
zone.id.clone(),
MemoryZone::new(zone.shared, zone.hugepages, zone_align_size),
MemoryZone::new(zone.shared, zone.hugepages, zone_align_size, zone.mergeable),
);
for ram_region in ram_regions.iter() {
@@ -701,7 +703,12 @@ impl MemoryManager {
}
memory_zones.insert(
zone.id.clone(),
MemoryZone::new(zone.shared, zone.hugepages, zone_align_size),
MemoryZone::new(
zone.shared,
zone.hugepages,
zone_align_size,
zone.mergeable,
),
);
}
@@ -733,7 +740,12 @@ impl MemoryManager {
let zone_page_size = memory_zone_get_align_size(zone_config)?;
memory_zones.insert(
zone_config.id.clone(),
MemoryZone::new(zone_config.shared, zone_config.hugepages, zone_page_size),
MemoryZone::new(
zone_config.shared,
zone_config.hugepages,
zone_page_size,
zone_config.mergeable,
),
);
}
@@ -1295,6 +1307,7 @@ impl MemoryManager {
hotplug_size: config.hotplug_size,
hotplugged_size: config.hotplugged_size,
prefault: config.prefault,
mergeable: config.mergeable,
}];
Ok((config.size, zones, allow_mem_hotplug))
@@ -1316,10 +1329,10 @@ impl MemoryManager {
regions.push((virtio_mem_zone.region().clone(), true));
}
list.push((zone_id.clone(), regions));
list.push((zone_id.clone(), regions, memory_zone.mergeable));
}
for (zone_id, regions) in list {
for (zone_id, regions, zone_mergeable) in list {
for (region, virtio_mem) in regions {
// SAFETY: guaranteed by GuestRegionMmap invariants
let slot = unsafe {
@@ -1327,7 +1340,7 @@ impl MemoryManager {
region.start_addr().raw_value(),
region.len().try_into().unwrap(),
region.as_ptr(),
self.mergeable,
zone_mergeable,
false,
self.log_dirty,
)
@@ -2087,7 +2100,9 @@ impl MemoryManager {
region.start_addr().0,
region.len().try_into().unwrap(),
region.as_ptr(),
self.mergeable,
self.memory_zones
.get(DEFAULT_MEMORY_ZONE)
.map_or(self.mergeable, |z| z.mergeable),
false,
self.log_dirty,
)

4
vmm/src/vm_config.rs
View File

@@ -159,7 +159,7 @@ pub struct PciSegmentConfig {
pub mmio64_aperture_weight: u32,
}
#[derive(Clone, Debug, PartialEq, Eq, Deserialize, Serialize)]
#[derive(Clone, Debug, Default, PartialEq, Eq, Deserialize, Serialize)]
pub struct MemoryZoneConfig {
pub id: String,
pub size: u64,
@@ -179,6 +179,8 @@ pub struct MemoryZoneConfig {
pub hotplugged_size: Option<u64>,
#[serde(default)]
pub prefault: bool,
#[serde(default)]
pub mergeable: bool,
}
impl ApplyLandlock for MemoryZoneConfig {