[Deepin-Kernel-SIG] [linux 6.18-y] [Openeuler] cgroup: disable kernel memory accounting for all memory cgroups by de…

[opsiff]

…fault

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8QLND CVE: NA

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The kernel memory accounting for all memory cgroups is not stable, and it will cause a 100% regression in hackbench compared with kernel-4.19, so disable it by default. We can use the following command line to enable or disable it:
cgroup.memory=kmem or cgroup.memory=nokmem.

(cherry picked from commit 53fbd8c)

Summary by Sourcery

Disable kernel memory accounting for memory cgroups by default and add a kernel parameter option to re-enable it.

Bug Fixes:

• Avoid performance regressions caused by unstable kernel memory accounting in memory cgroups by turning it off by default.

Documentation:

• Document the ability to toggle kernel memory accounting for memory cgroups via kernel parameters.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

This PR disables kernel memory accounting for memory cgroups by default and adds an explicit kernel parameter switch to re‑enable it, updating the memory cgroup documentation and kernel parameters docs accordingly.

Flow diagram for cgroup_memory kernel parameter handling

flowchart TD
    A[Boot_with_kernel_parameters] --> B[cgroup_memory parses parameters]
    B --> C{token_is_nokmem}
    B --> D{token_is_kmem}

    C -- yes --> E[set cgroup_memory_nokmem = true]
    C -- no --> F[no_change_from_nokmem]

    D -- yes --> G[set cgroup_memory_nokmem = false]
    D -- no --> H[no_change_from_kmem]

    I[default] --> J[cgroup_memory_nokmem = true]

Loading

File-Level Changes

Change	Details	Files
Disable kmem accounting for all memory cgroups by default, with a boot-time override.	Initialize cgroup_memory_nokmem to true so kernel memory accounting is off by default Extend cgroup_memory kernel parameter parsing to recognize "kmem" and explicitly clear cgroup_memory_nokmem when requested Retain existing handling of "nokmem" so boot parameters can still explicitly keep kmem disabled	mm/memcontrol.c
Document the default kmem accounting behavior and new kernel parameter toggle.	Update cgroup v1 memory controller documentation to describe default-disabled kmem accounting and the kmem/nokmem options Update kernel-parameters.txt to document cgroup.memory=kmem and cgroup.memory=nokmem boot parameters and their effects	Documentation/admin-guide/cgroup-v1/memory.rst Documentation/admin-guide/kernel-parameters.txt

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[Avenger-285714]

hulk inclusion category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I8QLND

So 6.6.y needs this too?

[sourcery-ai]

Hey - I've found 1 issue

Prompt for AI Agents

Please address the comments from this code review:

## Individual Comments

### Comment 1
<location path="Documentation/admin-guide/cgroup-v1/memory.rst" line_range="332-334" />
<code_context>
-at boot time. In this case, kernel memory will not be accounted at all.
+Kernel memory accounting is disabled for all memory cgroups by default. But
+it can be enabled system-wide by passing cgroup.memory=kmem to the kernel
+at boot time. In this case, kernel memory will all be accounted.

 Kernel memory limits are not imposed for the root cgroup. Usage for the root
</code_context>
<issue_to_address>
**suggestion (typo):** Clarify the phrasing "kernel memory will all be accounted" for better grammar.

Consider rephrasing to "kernel memory will be fully accounted" or "all kernel memory will be accounted for" to improve grammar and clarity.

```suggestion
Kernel memory accounting is disabled for all memory cgroups by default. But
it can be enabled system-wide by passing cgroup.memory=kmem to the kernel
at boot time. In this case, kernel memory will be fully accounted.
```
</issue_to_address>

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[sourcery-ai]

suggestion (typo): Clarify the phrasing "kernel memory will all be accounted" for better grammar.

Consider rephrasing to "kernel memory will be fully accounted" or "all kernel memory will be accounted for" to improve grammar and clarity.

Suggested change

	Kernel memory accounting is disabled for all memory cgroups by default. But
	it can be enabled system-wide by passing cgroup.memory=kmem to the kernel
	at boot time. In this case, kernel memory will all be accounted.
	Kernel memory accounting is disabled for all memory cgroups by default. But
	it can be enabled system-wide by passing cgroup.memory=kmem to the kernel
	at boot time. In this case, kernel memory will be fully accounted.

[Copilot]

Pull request overview

Disables kernel memory accounting for memory cgroups by default (to avoid reported performance regressions/instability) and adds a boot-time switch to re-enable it, updating the associated admin documentation.

Changes:

• Set cgroup_memory_nokmem default to true, disabling kmem accounting unless overridden.
• Extend cgroup.memory= boot parameter parsing to accept kmem (re-enables kmem accounting).
• Update kernel parameter and cgroup-v1 memory controller documentation to describe the new default and toggle.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
mm/memcontrol.c	Defaults kernel memory accounting to disabled and adds cgroup.memory=kmem parsing to re-enable it.
Documentation/admin-guide/kernel-parameters.txt	Documents the new cgroup.memory=kmem option.
Documentation/admin-guide/cgroup-v1/memory.rst	Updates the narrative to reflect kmem accounting being disabled by default and how to enable it.

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[opsiff]

hulk inclusion category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I8QLND

So 6.6.y needs this too?

6.6.y had it long long ago.....