1.\" $NetBSD: memoryallocators.9,v 1.6 2014/03/18 18:20:40 riastradh Exp $ 2.\" 3.\" Copyright (c) 2006 Elad Efrat <elad@NetBSD.org> 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. The name of the author may not be used to endorse or promote products 15.\" derived from this software without specific prior written permission. 16.\" 17.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 18.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 19.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 20.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 21.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 22.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 26.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27.\" 28.Dd August 3, 2009 29.Dt MEMORYALLOCATORS 9 30.Os 31.Sh NAME 32.Nm memoryallocators 33.Nd introduction to kernel memory allocators 34.Sh DESCRIPTION 35The 36.Nx 37kernel provides several memory allocators, each with different characteristics 38and purpose. 39This document summarizes the main differences between them. 40.Ss The Kmem Allocator 41The kmem allocator is modelled after an interface of similar name implemented in 42Solaris. 43This is main general purpose allocator in the kernel. 44.Pp 45It is implemented on-top of the 46.Xr vmem 9 47resource allocator (beyond the scope of this document), meaning it will be using 48.Xr pool_cache 9 49internally to speed-up common (small) sized allocations. 50.Pp 51It requires no setup, but cannot be used from interrupt context. 52.Pp 53See 54.Xr kmem 9 55for more details. 56.Ss The Pool Allocator 57The 58.Xr pool 9 59allocator is a fixed-size memory allocator. 60It requires setup (to initialize a memory pool) and is interrupt-safe. 61.Pp 62.\" On some architectures (foo, bar) the 63.\" .Xr pool 9 64.\" allocator will use direct-mapped segments rather than normal page 65.\" mappings, which can reduce TLB contentions. 66.\".Pp 67See 68.Xr pool 9 69for more details. 70.Ss The Pool Cache Allocator 71The pool cache allocator works on-top of the 72.Xr pool 9 73allocator, also allowing fixed-size allocation only, requires setup, 74and is interrupt-safe. 75.Pp 76The pool cache allocator is expected to be faster than other allocators, 77including the 78.Dq normal 79pool allocator. 80.Pp 81In the future this allocator is expected to have a per-CPU cache. 82.Pp 83See 84.Xr pool_cache 9 85for more details. 86.Ss The UVM Kernel Memory Allocator 87This is a low-level memory allocator interface. 88It allows variable-sized allocations in multiples of 89.Dv PAGE_SIZE , 90and can be used to allocate both wired and pageable kernel memory. 91.Pp 92See 93.Xr uvm 9 94for more details. 95.Sh SEE ALSO 96.Xr intro 9 , 97.Xr kmem 9 , 98.Xr pool 9 , 99.Xr pool_cache 9 , 100.Xr uvm 9 , 101.Xr vmem 9 102.Sh AUTHORS 103.An Elad Efrat Aq Mt elad@NetBSD.org 104.An YAMAMOTO Takashi Aq Mt yamt@NetBSD.org 105