kernel-memory-management

Original：🇺🇸 English

Translated

Kernel memory management skill for Linux mm subsystem. Use when using kmalloc, vmalloc, page allocator, SLUB, or debugging OOM and memory zones. Activates on queries about buddy allocator, kmalloc sizes, vmalloc vs kmalloc, SLUB, memory zones, or kernel OOM.

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Sourcemohitmishra786/low-level-dev-skills

Added on2026-08-20

NPX Install

npx skill4agent add mohitmishra786/low-level-dev-skills kernel-memory-management

SKILL.md Content

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Kernel Memory Management

Purpose

Guide agents through Linux kernel memory allocation: physical page allocator (buddy), SLUB kmalloc caches, vmalloc virtual mappings, zones (DMA/Normal), and safe allocation patterns in drivers — extending

skills/kernel/kernel-internals

.

When to Use

Choosing
```
kmalloc
```
vs
```
vmalloc
```
vs
```
get_free_pages
```
Debugging kernel OOM or slab corruption
DMA buffer allocation requirements
Understanding
```
/proc/meminfo
```
and slab stats

Workflow

1. Allocator decision tree

Need physically contiguous memory for DMA?
├── Yes → dma_alloc_coherent() or CMA pool
└── No
    ├── Size ≤ ~128K (arch-dependent) → kmalloc / kzalloc
    ├── Large or non-contiguous OK → vmalloc / vzalloc
    └── Whole pages → alloc_pages() / __get_free_pages()

2. kmalloc and SLUB

SLUB is the default general-purpose kmalloc backend (per kernel memory allocation guide); the legacy SLAB allocator was removed in Linux 6.12.

c

void *buf = kmalloc(size, GFP_KERNEL);
if (!buf)
    return -ENOMEM;
/* ... */
kfree(buf);

GFP flag	Context
`GFP_KERNEL`	Process context, may sleep
`GFP_ATOMIC`	IRQ / holding spinlock — smaller pools
`GFP_DMA`	DMA zone (legacy 32-bit devices)

Check

/proc/slabinfo

and

cat /sys/kernel/slab/*/object_size

.

3. vmalloc

c

void *v = vmalloc(size);  /* virtually contiguous, physically scattered */
vfree(v);

Use for large buffers where contiguous physical pages are unnecessary. Do not use for DMA without

dma_map_*

.

4. Buddy page allocator

c

struct page *page = alloc_pages(GFP_KERNEL, order);
void *addr = page_address(page);
__free_pages(page, order);

order

n allocates

2^n

pages. Zone selection:

ZONE_DMA

,

ZONE_NORMAL

,

ZONE_MOVABLE

(see

include/linux/mmzone.h

).

5. NUMA basics

On NUMA systems,

kmalloc

prefers local node; use

alloc_pages_node()

or

mbind

policies for HPC paths — see

skills/allocators/numa-programming

.

6. Debugging

bash

cat /proc/meminfo
cat /proc/slabinfo
dmesg | grep -i oom

Kernel config:

CONFIG_SLUB_DEBUG

,

CONFIG_KASAN

for use-after-free.

7. Agent usage

/kernel-memory-management Choose allocator for 2 MiB driver ring buffer in process context

Common Problems

Symptom	Cause	Fix
`kmalloc` fails large	Exceeds kmalloc limit	Use `vmalloc` or pages
DMA buffer wrong	Used `vmalloc` for HW DMA	`dma_alloc_coherent`
OOM killer	Unbounded cache growth	Limit pools; use shrinker
Slab corruption	Use-after-free	KASAN; audit `kfree` pairing
`GFP_KERNEL` in IRQ	Sleeping allocator in atomic	`GFP_ATOMIC`

Related Skills

```
skills/kernel/kernel-internals
```
— page cache, OOM killer

skills/kernel/device-drivers

—

dma_alloc_coherent

```
skills/allocators/custom-allocators
```
— userspace allocator design
```
skills/allocators/numa-programming
```
— NUMA-aware allocation
```
skills/runtimes/sanitizers
```
— KASAN overlap