NetBSD-5.0.2/share/man/man9/memoryallocators.9

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.\" $NetBSD: memoryallocators.9,v 1.3 2007/01/09 12:49:36 elad Exp $
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.\" Copyright (c) 2006 Elad Efrat <elad@NetBSD.org>
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.Dd January 7, 2007
.Dt MEMORYALLOCATORS 9
.Os
.Sh NAME
.Nm memoryallocators
.Nd introduction to kernel memory allocators
.Sh DESCRIPTION
The
.Nx
kernel provides several memory allocators, each with different characteristics
and purpose.
This document summarizes the main differences between them.
.Ss The Malloc Allocator
The
.Xr malloc 9
allocator can be used for variable-sized allocations in the kernel address
space.
It is interrupt-safe, requires no setup (see below), and is considered to be
stable (given the number of years it has been in the kernel).
.Pp
This interface also allows associating a
.Dq type
with an allocation to indicate what subsystem is using the memory allocated,
thus providing statistics as to the memory usage of different kernel subsystems.
To define a type, one should use the
.Dv MALLOC_DEFINE
macro, otherwise, one of the built-in types, like
.Dv M_TEMP
can be used.
.Pp
See
.Xr malloc 9
for more details.
.Ss The Kmem Allocator
The kmem allocator is modelled after an interface of similar name implemented in
Solaris, and is under active development.
.Pp
It is implemented on-top of the
.Xr vmem 9
resource allocator (beyond the scope of this document), meaning it will be using
.Xr pool_cache 9
internally to speed-up common (small) sized allocations.
.Pp
Like
.Xr malloc 9 ,
it requires no setup, but can't be used yet from interrupt context.
.Pp
See
.Xr kmem_alloc 9 ,
.Xr kmem_zalloc 9 ,
and
.Xr kmem_free 9
for more details.
.Ss The Pool Allocator
The
.Xr pool 9
allocator is a fixed-size memory allocator.
It requires setup (to initialize a memory pool) and is interrupt-safe.
.Pp
.\" On some architectures (foo, bar) the
.\" .Xr pool 9
.\" allocator will use direct-mapped segments rather than normal page
.\" mappings, which can reduce TLB contentions.
.\".Pp
See
.Xr pool 9
for more details.
.Ss The Pool Cache Allocator
The pool cache allocator works on-top of the
.Xr pool 9
allocator, also allowing fixed-size allocation only, requires setup,
and is interrupt-safe.
.Pp
The pool cache allocator is expected to be faster than other allocators,
including the
.Dq normal
pool allocator.
.Pp
In the future this allocator is expected to have a per-CPU cache.
.Pp
See
.Xr pool_cache 9
for more details.
.Ss The UVM Kernel Memory Allocator
This is a low-level memory allocator interface.
It allows variable-sized allocations in multiples of
.Dv PAGE_SIZE ,
and can be used to allocate both wired and pageable kernel memory.
.Pp
See
.Xr uvm 9
for more details.
.Sh SEE ALSO
.Xr free 9 ,
.Xr intro 9 ,
.Xr kmem_alloc 9 ,
.Xr kmem_free 9 ,
.Xr kmem_zalloc 9 ,
.Xr malloc 9 ,
.Xr pool 9 ,
.Xr pool_cache 9 ,
.Xr uvm 9 ,
.Xr vmem 9
.Sh AUTHORS
.An Elad Efrat Aq elad@NetBSD.org
.An YAMAMOTO Takashi Aq yamt@NetBSD.org