134 lines
4.2 KiB
Groff
134 lines
4.2 KiB
Groff
.\" $NetBSD: memoryallocators.9,v 1.3 2007/01/09 12:49:36 elad Exp $
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.\"
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.\" Copyright (c) 2006 Elad Efrat <elad@NetBSD.org>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd January 7, 2007
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.Dt MEMORYALLOCATORS 9
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.Os
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.Sh NAME
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.Nm memoryallocators
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.Nd introduction to kernel memory allocators
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.Sh DESCRIPTION
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The
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.Nx
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kernel provides several memory allocators, each with different characteristics
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and purpose.
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This document summarizes the main differences between them.
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.Ss The Malloc Allocator
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The
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.Xr malloc 9
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allocator can be used for variable-sized allocations in the kernel address
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space.
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It is interrupt-safe, requires no setup (see below), and is considered to be
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stable (given the number of years it has been in the kernel).
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.Pp
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This interface also allows associating a
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.Dq type
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with an allocation to indicate what subsystem is using the memory allocated,
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thus providing statistics as to the memory usage of different kernel subsystems.
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To define a type, one should use the
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.Dv MALLOC_DEFINE
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macro, otherwise, one of the built-in types, like
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.Dv M_TEMP
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can be used.
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.Pp
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See
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.Xr malloc 9
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for more details.
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.Ss The Kmem Allocator
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The kmem allocator is modelled after an interface of similar name implemented in
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Solaris, and is under active development.
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.Pp
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It is implemented on-top of the
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.Xr vmem 9
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resource allocator (beyond the scope of this document), meaning it will be using
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.Xr pool_cache 9
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internally to speed-up common (small) sized allocations.
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.Pp
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Like
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.Xr malloc 9 ,
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it requires no setup, but can't be used yet from interrupt context.
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.Pp
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See
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.Xr kmem_alloc 9 ,
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.Xr kmem_zalloc 9 ,
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and
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.Xr kmem_free 9
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for more details.
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.Ss The Pool Allocator
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The
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.Xr pool 9
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allocator is a fixed-size memory allocator.
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It requires setup (to initialize a memory pool) and is interrupt-safe.
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.Pp
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.\" On some architectures (foo, bar) the
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.\" .Xr pool 9
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.\" allocator will use direct-mapped segments rather than normal page
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.\" mappings, which can reduce TLB contentions.
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.\".Pp
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See
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.Xr pool 9
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for more details.
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.Ss The Pool Cache Allocator
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The pool cache allocator works on-top of the
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.Xr pool 9
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allocator, also allowing fixed-size allocation only, requires setup,
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and is interrupt-safe.
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.Pp
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The pool cache allocator is expected to be faster than other allocators,
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including the
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.Dq normal
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pool allocator.
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.Pp
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In the future this allocator is expected to have a per-CPU cache.
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.Pp
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See
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.Xr pool_cache 9
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for more details.
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.Ss The UVM Kernel Memory Allocator
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This is a low-level memory allocator interface.
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It allows variable-sized allocations in multiples of
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.Dv PAGE_SIZE ,
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and can be used to allocate both wired and pageable kernel memory.
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.Pp
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See
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.Xr uvm 9
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for more details.
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.Sh SEE ALSO
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.Xr free 9 ,
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.Xr intro 9 ,
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.Xr kmem_alloc 9 ,
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.Xr kmem_free 9 ,
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.Xr kmem_zalloc 9 ,
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.Xr malloc 9 ,
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.Xr pool 9 ,
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.Xr pool_cache 9 ,
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.Xr uvm 9 ,
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.Xr vmem 9
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.Sh AUTHORS
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.An Elad Efrat Aq elad@NetBSD.org
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.An YAMAMOTO Takashi Aq yamt@NetBSD.org
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