zephyr-memory

name	zephyr-memory
description	Expert guidance on Zephyr RTOS memory management (Heaps, Memory Slabs, Memory Blocks, Memory Domains, Virtual Memory). Use when the user asks about dynamic memory allocation, memory pools, k_malloc, k_heap, memory slabs, fixed-size allocators, memory protection, memory partitions, userspace memory isolation, virtual memory, demand paging, or choosing the right memory allocator in Zephyr.

Zephyr Memory Management

Overview

Zephyr provides multiple memory management mechanisms tailored for different embedded use cases. This skill helps select the right allocator, implement memory patterns correctly, and avoid common pitfalls.

Workflow

1. Allocator Selection

Determine requirements before choosing:

• Block size variability? Fixed vs variable-size allocations
• Determinism needed? Constant-time allocation requirements
• Fragmentation tolerance? Long-running systems need fragmentation resistance
• Memory protection? Userspace isolation requirements
• ISR context? Some allocators cannot be used from ISRs

Step 1: Read references/comparison.md for the allocator decision matrix.

2. Implementation

Once the allocator is selected, implement using the appropriate guide.

Step 2: Read the appropriate reference:

• Heaps: references/heaps.md — Variable-size dynamic allocation (k_heap, k_malloc, sys_heap).
• Memory Slabs: references/slabs.md — Fixed-size block allocation with zero fragmentation.
• Memory Blocks: references/mem_blocks.md — Multi-block allocator with external bookkeeping.
• Memory Domains: references/domains.md — Memory partitions for userspace thread isolation.
• Virtual Memory: references/virtual.md — MMU-based memory mapping and demand paging.

3. API & Configuration

For complete API signatures and Kconfig options.

Step 3: Read references/api.md for:

• Complete API function signatures for all allocators.
• Relevant Kconfig options.
• Header file locations.

4. Troubleshooting

Common memory management issues:

• Fragmentation: Use slabs or mem_blocks for fixed-size allocations; prefer multiple purpose-specific heaps over one large heap.
• Stack overflow: Enable CONFIG_HW_STACK_PROTECTION; size stacks appropriately with CONFIG_*_STACK_SIZE.
• ISR allocation failures: Never block in ISRs; use K_NO_WAIT and handle allocation failures.
• Memory leaks: Track allocations; use heap listeners (CONFIG_HEAP_LISTENER) for debugging.
• Userspace access violations: Verify memory partitions are correctly configured and threads are assigned to the right domains.

Source Locations

Description	Path
Memory Management Docs	<zephyr-ws>/deps/zephyr/doc/kernel/memory_management
Memory Domain Docs	<zephyr-ws>/deps/zephyr/doc/kernel/usermode/memory_domain.rst
Memory Services Docs	<zephyr-ws>/deps/zephyr/doc/services/mem_mgmt
Kernel Header	<zephyr-ws>/deps/zephyr/include/zephyr/kernel.h
Sys Heap Header	<zephyr-ws>/deps/zephyr/include/zephyr/sys/sys_heap.h
Mem Blocks Header	<zephyr-ws>/deps/zephyr/include/zephyr/sys/mem_blocks.h
Mem Domain Header	<zephyr-ws>/deps/zephyr/include/zephyr/app_memory/mem_domain.h
Heap Sample	<zephyr-ws>/deps/zephyr/samples/kernel/heap
Slab Sample	<zephyr-ws>/deps/zephyr/samples/kernel/mem_slab

Note: <zephyr-ws> represents the root of the Zephyr workspace.