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config-linux: add memory.checkBeforeUpdate #1158

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Merged
merged 1 commit into from
Sep 9, 2022
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config-linux: add memory.checkBeforeUpdate #1158

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5 changes: 5 additions & 0 deletions config-linux.md
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Expand Up @@ -336,6 +336,11 @@ The following properties do not specify memory limits, but are covered by the `m
To disable it, specify a value of `true`.
* **`useHierarchy`** *(bool, OPTIONAL)* - enables or disables hierarchical memory accounting.
If enabled (`true`), child cgroups will share the memory limits of this cgroup.
* **`checkBeforeUpdate`** *(bool, OPTIONAL)* - enables container memory usage check before setting a new limit.
If enabled (`true`), runtime MAY check if a new memory limit is lower than the current usage, and MUST
reject the new limit. Practically, when cgroup v1 is used, the kernel rejects the limit lower than the
current usage, and when cgroup v2 is used, an OOM killer is invoked. This setting can be used on
cgroup v2 to mimic the cgroup v1 behavior.
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Should we call out that there is TOCTOU race possible here and it won't be able to exactly match cgroups v1 behavior?

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To me this is an implementation detail, and this is merely a spec. In fact it should not even explain why we need it, but I guess some context would not hurt.


#### Example

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3 changes: 3 additions & 0 deletions schema/config-linux.json
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Expand Up @@ -169,6 +169,9 @@
},
"useHierarchy": {
"type": "boolean"
},
"checkBeforeUpdate": {
"type": "boolean"
}
}
},
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3 changes: 2 additions & 1 deletion schema/test/config/good/spec-example.json
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Expand Up @@ -270,7 +270,8 @@
"kernelTCP": -1,
"swappiness": 0,
"disableOOMKiller": false,
"useHierarchy": false
"useHierarchy": false,
"checkBeforeUpdate": false
},
"cpu": {
"shares": 1024,
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4 changes: 4 additions & 0 deletions specs-go/config.go
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Expand Up @@ -319,6 +319,10 @@ type LinuxMemory struct {
DisableOOMKiller *bool `json:"disableOOMKiller,omitempty"`
// Enables hierarchical memory accounting
UseHierarchy *bool `json:"useHierarchy,omitempty"`
// CheckBeforeUpdate enables checking if a new memory limit is lower
// than the current usage during update, and if so, rejecting the new
// limit.
CheckBeforeUpdate *bool `json:"checkBeforeUpdate,omitempty"`
}

// LinuxCPU for Linux cgroup 'cpu' resource management
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