Manual browser: memoryallocators(9)



memoryallocatorsintroduction to kernel memory allocators


The NetBSD kernel provides several memory allocators, each with different characteristics and purpose. This document summarizes the main differences between them.

The Kmem Allocator

The kmem allocator is modelled after an interface of similar name implemented in Solaris. This is main general purpose allocator in the kernel.

It is implemented on-top of the vmem(9) resource allocator (beyond the scope of this document), meaning it will be using pool_cache(9) internally to speed-up common (small) sized allocations.

It requires no setup, but cannot be used from interrupt context.

See kmem(9) for more details.

The Pool Allocator

The pool(9) allocator is a fixed-size memory allocator. It requires setup (to initialize a memory pool) and is interrupt-safe.

See pool(9) for more details.

The Pool Cache Allocator

The pool cache allocator works on-top of the pool(9) allocator, also allowing fixed-size allocation only, requires setup, and is interrupt-safe.

The pool cache allocator is expected to be faster than other allocators, including the “normal” pool allocator.

In the future this allocator is expected to have a per-CPU cache.

See pool_cache(9) for more details.

The UVM Kernel Memory Allocator

This is a low-level memory allocator interface. It allows variable-sized allocations in multiples of PAGE_SIZE, and can be used to allocate both wired and pageable kernel memory.

See uvm(9) for more details.


Elad Efrat <> YAMAMOTO Takashi <>
August 3, 2009 NetBSD 7.0