1.\" 2.\" Copyright (c) 1996 The NetBSD Foundation, Inc. 3.\" All rights reserved. 4.\" 5.\" This code is derived from software contributed to The NetBSD Foundation 6.\" by Paul Kranenburg. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. All advertising materials mentioning features or use of this software 17.\" must display the following acknowledgement: 18.\" This product includes software developed by the NetBSD 19.\" Foundation, Inc. and its contributors. 20.\" 4. Neither the name of The NetBSD Foundation nor the names of its 21.\" contributors may be used to endorse or promote products derived 22.\" from this software without specific prior written permission. 23.\" 24.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 25.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 26.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 27.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE 28.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 29.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 30.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 31.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 32.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 33.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 34.\" POSSIBILITY OF SUCH DAMAGE. 35.\" 36.\" $NetBSD: malloc.9,v 1.3 1996/11/11 00:05:11 lukem Exp $ 37.\" $FreeBSD$ 38.\" 39.Dd October 23, 2008 40.Dt MALLOC 9 41.Os 42.Sh NAME 43.Nm malloc , 44.Nm free , 45.Nm realloc , 46.Nm reallocf , 47.Nm MALLOC_DEFINE , 48.Nm MALLOC_DECLARE 49.Nd kernel memory management routines 50.Sh SYNOPSIS 51.In sys/types.h 52.In sys/malloc.h 53.Ft void * 54.Fn malloc "unsigned long size" "struct malloc_type *type" "int flags" 55.Ft void 56.Fn free "void *addr" "struct malloc_type *type" 57.Ft void * 58.Fn realloc "void *addr" "unsigned long size" "struct malloc_type *type" "int flags" 59.Ft void * 60.Fn reallocf "void *addr" "unsigned long size" "struct malloc_type *type" "int flags" 61.Fn MALLOC_DECLARE type 62.In sys/param.h 63.In sys/malloc.h 64.In sys/kernel.h 65.Fn MALLOC_DEFINE type shortdesc longdesc 66.Sh DESCRIPTION 67The 68.Fn malloc 69function allocates uninitialized memory in kernel address space for an 70object whose size is specified by 71.Fa size . 72.Pp 73The 74.Fn free 75function releases memory at address 76.Fa addr 77that was previously allocated by 78.Fn malloc 79for re-use. 80The memory is not zeroed. 81If 82.Fa addr 83is 84.Dv NULL , 85then 86.Fn free 87does nothing. 88.Pp 89The 90.Fn realloc 91function changes the size of the previously allocated memory referenced by 92.Fa addr 93to 94.Fa size 95bytes. 96The contents of the memory are unchanged up to the lesser of the new and 97old sizes. 98Note that the returned value may differ from 99.Fa addr . 100If the requested memory cannot be allocated, 101.Dv NULL 102is returned and the memory referenced by 103.Fa addr 104is valid and unchanged. 105If 106.Fa addr 107is 108.Dv NULL , 109the 110.Fn realloc 111function behaves identically to 112.Fn malloc 113for the specified size. 114.Pp 115The 116.Fn reallocf 117function is identical to 118.Fn realloc 119except that it 120will free the passed pointer when the requested memory cannot be allocated. 121.Pp 122Unlike its standard C library counterpart 123.Pq Xr malloc 3 , 124the kernel version takes two more arguments. 125The 126.Fa flags 127argument further qualifies 128.Fn malloc Ns 's 129operational characteristics as follows: 130.Bl -tag -width indent 131.It Dv M_ZERO 132Causes the allocated memory to be set to all zeros. 133.It Dv M_NOWAIT 134Causes 135.Fn malloc , 136.Fn realloc , 137and 138.Fn reallocf 139to return 140.Dv NULL 141if the request cannot be immediately fulfilled due to resource shortage. 142Note that 143.Dv M_NOWAIT 144is required when running in an interrupt context. 145.It Dv M_WAITOK 146Indicates that it is OK to wait for resources. 147If the request cannot be immediately fulfilled, the current process is put 148to sleep to wait for resources to be released by other processes. 149The 150.Fn malloc , 151.Fn realloc , 152and 153.Fn reallocf 154functions cannot return 155.Dv NULL 156if 157.Dv M_WAITOK 158is specified. 159.It Dv M_USE_RESERVE 160Indicates that the system can dig into its reserve in order to obtain the 161requested memory. 162This option used to be called 163.Dv M_KERNEL 164but has been renamed to something more obvious. 165This option has been deprecated and is slowly being removed from the kernel, 166and so should not be used with any new programming. 167.El 168.Pp 169Exactly one of either 170.Dv M_WAITOK 171or 172.Dv M_NOWAIT 173must be specified. 174.Pp 175The 176.Fa type 177argument is used to perform statistics on memory usage, and for 178basic sanity checks. 179It can be used to identify multiple allocations. 180The statistics can be examined by 181.Sq vmstat -m . 182.Pp 183A 184.Fa type 185is defined using 186.Vt "struct malloc_type" 187via the 188.Fn MALLOC_DECLARE 189and 190.Fn MALLOC_DEFINE 191macros. 192.Bd -literal -offset indent 193/* sys/something/foo_extern.h */ 194 195MALLOC_DECLARE(M_FOOBUF); 196 197/* sys/something/foo_main.c */ 198 199MALLOC_DEFINE(M_FOOBUF, "foobuffers", "Buffers to foo data into the ether"); 200 201/* sys/something/foo_subr.c */ 202 203\&... 204buf = malloc(sizeof *buf, M_FOOBUF, M_NOWAIT); 205 206.Ed 207.Pp 208In order to use 209.Fn MALLOC_DEFINE , 210one must include 211.In sys/param.h 212(instead of 213.In sys/types.h ) 214and 215.In sys/kernel.h . 216.Sh IMPLEMENTATION NOTES 217The memory allocator allocates memory in chunks that have size a power 218of two for requests up to the size of a page of memory. 219For larger requests, one or more pages is allocated. 220While it should not be relied upon, this information may be useful for 221optimizing the efficiency of memory use. 222.Pp 223Programmers should be careful not to confuse the malloc flags 224.Dv M_NOWAIT 225and 226.Dv M_WAITOK 227with the 228.Xr mbuf 9 229flags 230.Dv M_DONTWAIT 231and 232.Dv M_WAIT . 233.Sh CONTEXT 234.Fn malloc , 235.Fn realloc 236and 237.Fn reallocf 238may not be called from fast interrupts handlers. 239When called from threaded interrupts, 240.Fa flags 241must contain 242.Dv M_NOWAIT . 243.Pp 244.Fn malloc , 245.Fn realloc 246and 247.Fn reallocf 248may sleep when called with 249.Dv M_WAITOK . 250.Fn free 251never sleeps. 252.Pp 253Any calls to 254.Fn malloc 255(even with 256.Dv M_NOWAIT ) 257or 258.Fn free 259when holding a 260.Xr vnode 9 261interlock, will cause a LOR (Lock Order Reversal) due to the 262intertwining of VM Objects and Vnodes. 263.Sh RETURN VALUES 264The 265.Fn malloc , 266.Fn realloc , 267and 268.Fn reallocf 269functions return a kernel virtual address that is suitably aligned for 270storage of any type of object, or 271.Dv NULL 272if the request could not be satisfied (implying that 273.Dv M_NOWAIT 274was set). 275.Sh DIAGNOSTICS 276A kernel compiled with the 277.Dv INVARIANTS 278configuration option attempts to detect memory corruption caused by 279such things as writing outside the allocated area and imbalanced calls to the 280.Fn malloc 281and 282.Fn free 283functions. 284Failing consistency checks will cause a panic or a system console 285message. 286.Sh SEE ALSO 287.Xr vmstat 8 , 288.Xr contigmalloc 9 , 289.Xr memguard 9 , 290.Xr vnode 9 291