.\" (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" License.
.\" Modified Sat Jul 24 19:00:59 1993 by Rik Faith (faith@cs.unc.edu)
.\" Clarification concerning realloc, iwj10@cus.cam.ac.uk (Ian Jackson), 950701
.\" Documented MALLOC_CHECK_, Wolfram Gloger (wmglo@dent.med.uni-muenchen.de)
.\" 2007-09-15 mtk: added notes on malloc()'s use of sbrk() and mmap().
.\"
.\" Japanese Version Copyright (c) 1998 NAKANO Takeo all rights reserved.
.\" Translated 1998-08-12, NAKANO Takeo <nakano@apm.seikei.ac.jp>
.\" Modified 1998-12-18, NAKANO Takeo
.\" Modified 2000-08-23, NAKANO Takeo
.\" Modified 2001-05-19, Kentaro Shirakata <argrath@ub32.org>
.\" Modified 2001-12-13, Kentaro Shirakata <argrath@ub32.org>
.\" Modified 2005-03-15, Akihiro MOTOKI <amotoki@dd.iij4u.or.jp>
.\" Modified 2007-10-12, Akihiro MOTOKI, LDP v2.66
.\"
.\" WORD: OOM killer	­
.\"
.TH MALLOC 3  2008-02-22 "GNU" "Linux Programmer's Manual"
.SH ̾
calloc, malloc, free, realloc \- ưŪʥγƤȲԤ
.SH 
.nf
.B #include <stdlib.h>
.sp
.BI "void *calloc(size_t " "nmemb" ", size_t " "size" );
.br
.BI "void *malloc(size_t " "size" );
.br
.BI "void free(void " "*ptr" );
.br
.BI "void *realloc(void " "*ptr" ", size_t "  "size" );
.fi
.SH 
.BR calloc ()

.I size
ХȤ
.I nmemb
Ĥʤ˥ơ
Ƥ줿Фݥ󥿤֤
ƤϿͥ (ӥåȤΥХ) ˥åȤ롣
.I nmemb

.I size
 0 ξ硢
.BR calloc ()
 NULL
.\" glibc Ϥ
ޤ
.BR free ()
˸ϤƤεʤդʥݥ֤ͤ
.PP
.BR malloc ()

.I size
ХȤơ
Ƥ줿Фݥ󥿤֤
Ƥϥꥢʤ
.I size
 0 ξ硢
.BR malloc ()
 NULL
.\" glibc Ϥ
ޤ
.BR free ()
˸ϤƤεʤդʥݥ֤ͤ
.PP
.BR free ()
ϥݥ
.I ptr
ؤ֤롣Υݥ󥿤ϡ˸ƤӽФ줿
.BR malloc (),
.BR calloc (),
.BR realloc ()
Τ줫֤ͤǤʤФʤʤ
ʳΥݥ󥿤ꤷꡢǤ
.I free(ptr)
¹ԤƤꤷưƤʤ
.I ptr
 NULL ξˤϡʤưԤʤ
.PP
.BR realloc ()
ϡݥ
.I ptr
֥åΥѹ
.I size
ХȤˤ롣
ΥΤۤΥ֥å˴ޤޤƤѹʤ
Ƥ줿ƤϽʤ
.I size
ɤͤǤäƤ⡢
.I ptr
 NULL ξˤ
.I malloc(size)
Ǥ롣
.I size
 0 
.I ptr
 NULL Ǥʤˤϡ
.I free(ptr)
Ǥ롣
.I ptr
 NULL ʳξ硢
.I ptr
ϰ˸ƤӽФ줿
.BR malloc (),
.BR calloc (),
.BR realloc ()
Τ줫֤ͤǤʤФʤʤ
.I ptr
ؤΰ褬ưƤ
.I free(ptr)
¹Ԥ롣
.SH ֤
.BR calloc ()

.BR malloc ()
֤ͤϡƤ줿ؤΥݥ󥿤Ǥ롣
ϤѿбǤ褦˥饤ȤƤ롣
׵˼Ԥ NULL ֤롣
.PP
.BR free ()
֤ͤʤ
.PP
.BR realloc ()
Ͽ˳Ƥ줿ؤΥݥ󥿤֤
ϤѿбǤ褦˥饤ȤƤꡢ
.I ptr
Ȥϰۤʤ뤳Ȥ⤢롣
׵˼Ԥ NULL ֤롣
.I size
 0 ξˤϡNULL ⤷
.BR free ()
ϤȤǤݥ󥿤֤롣
.BR realloc ()
ԤˤϡΥ֥åѹʤ
Ĥޤꡢ줿ư줿Ϥʤ
.SH 
C89, C99.
.SH 
̾
.BR malloc ()
ϡҡפơɬפ˱ƥҡפΥ
.BR sbrk (2)
ȤäĴ᤹롣
.B MMAP_THRESHOLD
ХȤ礭ʥ֥åƤ硢
glibc 
.BR malloc ()

.BR mmap (2)
Ȥäƥץ饤١Ȥ̵̾ޥåԥ (anonymous mapping) Ȥ
Ƥ롣
ǥեȤǤ
.B MMAP_THRESHOLD
 128 kB 
.BR mallopt (3)
ȤäĴǤ롣
.\" FIXME . there is no mallopt(3) man page yet.
.BR mmap (2)
ȤäƹԤ줿Ƥ
.B RLIMIT_DATA
꥽¤αƶʤ
.RB ( getrlimit (2)
)

Unix98 ɸǤϡ
.BR malloc (),
.BR calloc (),
.BR realloc ()
ϼ¹Ԥ˼ԤȤ
.I errno

.B ENOMEM
ꤹ뤳ȤˤʤäƤ롣
Glibc ǤϤ줬Ƥ뤳ȤꤷƤ
(ޤΥ롼 glibc СϤΤȤäƤ)
ĿṲ̄ malloc μȤäƤơ malloc 
.I errno
ꤷʤˤϡԤݤ
.I errno
˥顼ͳꤷʤ饤֥롼󤬤뤫⤷ʤ
.LP
.BR malloc (),
.BR calloc (),
.BR realloc (),
.BR free ()
ˤΤϡ
ۤȤɤξϥҡפ˲ (corruption) Ǥ롣
㤨СƤ줿ΰ򥪡Сե롢
Ʊݥ󥿤 free 롢ʤɤˤ롣
.PP
ǶΥС Linux libc (5.4.23 ʹ)  glibc (2.x) Ǥϡ
.BR malloc ()
ưĶѿˤäǤ褦ʼƤ롣
.B MALLOC_CHECK_
ꤵƤȡüʼѤ졢
ñʥ顼ˤѤ뤳ȤǤ褦ˤʤ (Ψϰʤ)㤨С
.BR free ()
ƱٸƤӽФƤޤ
1 ХȤԤƤޤ (off-by-one Х) ʤɤ롣
Υ顼ƤɤȤǤ櫓ǤϤʤ
ξˤϥ꡼äƤޤ
.B MALLOC_CHECK_
 0 ˥åȤƤȡҡפ˲ۤä̵뤹롣
1 ˥åȤƤȡǥåɸ२顼Ϥɽ롣
2 ˥åȤƤȡ
.BR abort (3)
ƤӽФ롣
3 ˥åȤƤȡǥåɸ२顼Ϥɽ졢
ץ϶λ (abort) 롣
.B MALLOC_CHECK_
 0 ʳͤ򥻥åȤΩľȤƤϡ
ºݤΥץΥå夬äȸ˵ꡢ
θõФΤ˺ʾʤɤ󤲤
.SH Х
ǥեȤǤϡLinux ϳڴŪάѤƤ롣
Ĥޤꡢ
.BR malloc ()
 NULL Ǥʤ֤ͤƤ⡢Υ꤬ºݤѲǽǤ뤳Ȥ
ݾڤʤˤޤХǤ롣
ƥब­֤ˤʤäȤ̾⤤­ (OOM killer)
ˤäưĤޤʣΥץ롣
ץΤ˾ޤʤǻѤƤơ
⥫ͥΥС󤬽ʬ˺ǶΤΤǤСΥ
Ʋ᤮ư (overcommitting behavior) ʲΥޥɤ
̵ˤǤ롣
.in +4n
.sp
.nf
# echo 2 > /proc/sys/vm/overcommit_memory

.fi
.in
ͥ°ʸ
.I vm/overcommit-accounting

.I sysctl/vm.txt
⻲ȤΤȡ
.SH Ϣ
.BR brk (2),
.BR posix_memalign (3)
.\" .BR mallopt (3),
.BR mmap (2),
.BR alloca (3),