The memory control group (memcg) quality of service (QoS) feature can be used to control locks and limits on memory usage in a memcg. In community versions of the Linux kernel, this feature is supported only by the cgroup v2 interface. In Alibaba Cloud Linux 2 starting with kernel version 4.19.91-18.al7 and Alibaba Cloud Linux 3, the memcg QoS feature is supported by the cgroup v1 interface.
Background information
In the Alibaba Cloud Linux kernel, the memcg QoS feature is enabled in the cgroup v1 interface by default. For more information about memcg QoS, see Documentation/admin-guide/cgroup-v2.rst. You can obtain the kernel document from the Debuginfo package and source code package of Alibaba Cloud Linux. For more information, see Use Alibaba Cloud Linux 2.
Precautions
When you use the memcg QoS feature of the cgroup v1 interface, we recommend that you place your tasks in a memcg leaf node. Sample task path: /sys/fs/cgroup/memory/<intermediate node>/<leaf node>/tasks.
Interface description
The following table describes the interfaces that implement the memcg QoS feature of the cgroup v1 interface in the Alibaba Cloud Linux kernel.
Interface | Description |
memory.min | Absolutely locks the memory. Memory locked by this interface cannot be reclaimed. You can perform the following read and write operations on the interface:
|
memory.low | Relatively locks the memory. Memory locked by this interface may be partially reclaimed if the system has no other memory to reclaim. You can perform the following read and write operations on the interface:
|
memory.high | Limits the memory usage. You can perform the following read and write operations on the interface:
|
Examples
Create a test memcg in the memcg mount directory such as /sys/fs/cgroup/memory/. Make sure that the memcg contains the memory.min, memory.low, and memory.high interfaces.
Sample command:
mkdir /sys/fs/cgroup/memory/test
ls /sys/fs/cgroup/memory/test | grep -E "memory.(min|low|high)"Sample output:
memory.high
memory.low
memory.min