Docker Memory Limits: Options and Descriptions

2nd chunk of `content/manuals/engine/containers/resource_constraints.md`

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### Limit a container's access to memory

Docker can enforce hard or soft memory limits.

- Hard limits let the container use no more than a fixed amount of memory.
- Soft limits let the container use as much memory as it needs unless certain
  conditions are met, such as when the kernel detects low memory or contention on
  the host machine.

Some of these options have different effects when used alone or when more than
one option is set.

Most of these options take a positive integer, followed by a suffix of `b`, `k`,
`m`, `g`, to indicate bytes, kilobytes, megabytes, or gigabytes.

| Option                 | Description                                                                                                                                                                                                                                                                                                                                                                                     |
| :--------------------- | :---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `-m` or `--memory=`    | The maximum amount of memory the container can use. If you set this option, the minimum allowed value is `6m` (6 megabytes). That is, you must set the value to at least 6 megabytes.                                                                                                                                                                                                           |
| `--memory-swap`\*      | The amount of memory this container is allowed to swap to disk. See [`--memory-swap` details](#--memory-swap-details).                                                                                                                                                                                                                                                                          |
| `--memory-swappiness`  | By default, the host kernel can swap out a percentage of anonymous pages used by a container. You can set `--memory-swappiness` to a value between 0 and 100, to tune this percentage. See [`--memory-swappiness` details](#--memory-swappiness-details).                                                                                                                                       |
| `--memory-reservation` | Allows you to specify a soft limit smaller than `--memory` which is activated when Docker detects contention or low memory on the host machine. If you use `--memory-reservation`, it must be set lower than `--memory` for it to take precedence. Because it is a soft limit, it doesn't guarantee that the container doesn't exceed the limit.                                                |
| `--kernel-memory`      | The maximum amount of kernel memory the container can use. The minimum allowed value is `6m`. Because kernel memory can't be swapped out, a container which is starved of kernel memory may block host machine resources, which can have side effects on the host machine and on other containers. See [`--kernel-memory` details](#--kernel-memory-details).                                   |
| `--oom-kill-disable`   | By default, if an out-of-memory (OOM) error occurs, the kernel kills processes in a container. To change this behavior, use the `--oom-kill-disable` option. Only disable the OOM killer on containers where you have also set the `-m/--memory` option. If the `-m` flag isn't set, the host can run out of memory and the kernel may need to kill the host system's processes to free memory. |

For more information about cgroups and memory in general, see the documentation
for [Memory Resource Controller](https://www.kernel.org/doc/Documentation/cgroup-v1/memory.txt).

Title: Docker Memory Limits: Options and Descriptions

Summary

Docker allows setting hard or soft memory limits for containers. Hard limits enforce a fixed memory cap, while soft limits allow dynamic memory allocation based on host conditions. Several options are available, including `--memory` (maximum memory), `--memory-swap` (swap allowance), `--memory-swappiness` (kernel swap percentage), `--memory-reservation` (soft limit for contention), `--kernel-memory` (maximum kernel memory), and `--oom-kill-disable` (disable OOM killer). Using these options effectively requires understanding their individual effects and interactions. When disabling the OOM killer, it's crucial to set a memory limit to prevent host-level memory exhaustion.