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[linuxjm/jm.git] / manual / LDP_man-pages / draft / man3 / malloc.3

.\" Copyright (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.\" manual page may be incorrect or out-of-date.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    ¥á¥â¥êÉÔ­²ò·è´ï
.\"
.TH MALLOC 3  2009-01-13 "GNU" "Linux Programmer's Manual"
.\"O .SH NAME
.\"O calloc, malloc, free, realloc \- Allocate and free dynamic memory
.SH ̾Á°
calloc, malloc, free, realloc \- ưŪ¤Ê¥á¥â¥ê¤Î³ä¤êÅö¤Æ¤È²òÊü¤ò¹Ô¤¦
.\"O .SH SYNOPSIS
.SH ½ñ¼°
.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
.\"O .SH DESCRIPTION
.SH ÀâÌÀ
.\"O .BR calloc ()
.\"O allocates memory for an array of
.\"O .I nmemb
.\"O elements of
.\"O .I size
.\"O bytes each and returns a pointer to the allocated memory.
.\"O The memory is set to zero.
.BR calloc ()
¤Ï
.I size
¥Ð¥¤¥È¤ÎÍ×ÁÇ
.I nmemb
¸Ä¤«¤é¤Ê¤ëÇÛÎó¤Ë¥á¥â¥ê¤ò³ä¤êÅö¤Æ¡¢
³ä¤êÅö¤Æ¤é¤ì¤¿¥á¥â¥ê¤ËÂФ¹¤ë¥Ý¥¤¥ó¥¿¤òÊÖ¤¹¡£
¥á¥â¥ê¤ÎÆâÍƤϿôÃÍ¥¼¥í (Á´¥Ó¥Ã¥È¤¬¥¼¥í¤Î¥Ð¥¤¥È) ¤Ë¥»¥Ã¥È¤µ¤ì¤ë¡£
.\"O If
.\"O .I nmemb
.\"O or
.\"O .I size
.\"O is 0, then
.\"O .BR calloc ()
.\"O returns either NULL,
.\"O .\" glibc does this:
.\"O or a unique pointer value that can later be successfully passed to
.\"O .BR free ().
.I nmemb
¤«
.I size
¤¬ 0 ¤Î¾ì¹ç¡¢
.BR calloc ()
¤Ï NULL
.\" glibc ¤Ï¤³¤Á¤é
¤Þ¤¿¤Ï
.BR free ()
¤Ë¸å¤ÇÅϤ·¤Æ¤âÌäÂê¤Îµ¯¤³¤é¤Ê¤¤°ì°Õ¤Ê¥Ý¥¤¥ó¥¿ÃͤòÊÖ¤¹¡£
.PP
.\"O .BR malloc ()
.\"O allocates
.\"O .I size
.\"O bytes and returns a pointer to the allocated memory.
.\"O The memory is not cleared.
.BR malloc ()
¤Ï
.I size
¥Ð¥¤¥È¤ò³ä¤êÅö¤Æ¡¢
³ä¤êÅö¤Æ¤é¤ì¤¿¥á¥â¥ê¤ËÂФ¹¤ë¥Ý¥¤¥ó¥¿¤òÊÖ¤¹¡£
¥á¥â¥ê¤ÎÆâÍƤϥ¯¥ê¥¢¤µ¤ì¤Ê¤¤¡£
.\"O If
.\"O .I size
.\"O is 0, then
.\"O .BR malloc ()
.\"O returns either NULL,
.\"O .\" glibc does this:
.\"O or a unique pointer value that can later be successfully passed to
.\"O .BR free ().
.I size
¤¬ 0 ¤Î¾ì¹ç¡¢
.BR malloc ()
¤Ï NULL
.\" glibc ¤Ï¤³¤Á¤é
¤Þ¤¿¤Ï
.BR free ()
¤Ë¸å¤ÇÅϤ·¤Æ¤âÌäÂê¤Îµ¯¤³¤é¤Ê¤¤°ì°Õ¤Ê¥Ý¥¤¥ó¥¿ÃͤòÊÖ¤¹¡£
.PP
.\"O .BR free ()
.\"O frees the memory space pointed to by
.\"O .IR ptr ,
.\"O which must have been returned by a previous call to
.\"O .BR malloc (),
.\"O .BR calloc ()
.\"O or
.\"O .BR realloc ().
.\"O Otherwise, or if
.\"O .I free(ptr)
.\"O has already been called before, undefined behavior occurs.
.\"O If
.\"O .I ptr
.\"O is NULL, no operation is performed.
.BR free ()
¤Ï¥Ý¥¤¥ó¥¿
.I ptr
¤¬»Ø¤¹¥á¥â¥ê¶õ´Ö¤ò²òÊü¤¹¤ë¡£¤³¤Î¥Ý¥¤¥ó¥¿¤Ï¡¢°ÊÁ°¤Ë¸Æ¤Ó½Ð¤µ¤ì¤¿
.BR malloc (),
.BR calloc (),
.BR realloc ()
¤Î¤¤¤º¤ì¤«¤¬ÊÖ¤·¤¿ÃͤǤʤ±¤ì¤Ð¤Ê¤é¤Ê¤¤¡£
¤³¤ì°Ê³°¤Î¥Ý¥¤¥ó¥¿¤ò»ØÄꤷ¤¿¤ê¡¢¤¹¤Ç¤Ë
.I free(ptr)
¤¬¼Â¹Ô¤µ¤ì¤Æ¤¤¤¿¤ê¤·¤¿¾ì¹ç¤ÎÆ°ºî¤ÏÄêµÁ¤µ¤ì¤Æ¤¤¤Ê¤¤¡£
.I ptr
¤¬ NULL ¤Î¾ì¹ç¤Ë¤Ï¡¢¤Ê¤ó¤ÎÆ°ºî¤â¹Ô¤ï¤ì¤Ê¤¤¡£
.PP
.\"O .BR realloc ()
.\"O changes the size of the memory block pointed to by
.\"O .I ptr
.\"O to
.\"O .I size
.\"O bytes.
.BR realloc ()
¤Ï¡¢¥Ý¥¤¥ó¥¿
.I ptr
¤¬¼¨¤¹¥á¥â¥ê¥Ö¥í¥Ã¥¯¤Î¥µ¥¤¥º¤òÊѹ¹¤·¤Æ
.I size
¥Ð¥¤¥È¤Ë¤¹¤ë¡£
.\"O The contents will be unchanged to the minimum of the old and new sizes;
.\"O newly allocated memory will be uninitialized.
¿·µì¤Î¥µ¥¤¥º¤Î¤¦¤Á¡¢¾®¤µ¤¤¤Û¤¦¤Î¥Ö¥í¥Ã¥¯¤Ë´Þ¤Þ¤ì¤ëÆâÍƤÏÊѹ¹¤µ¤ì¤Ê¤¤¡£
¿·¤·¤¯³ä¤êÅö¤Æ¤é¤ì¤¿¥á¥â¥ê¤ÎÆâÍƤϽé´ü²½¤µ¤ì¤Ê¤¤¡£
.\"O If
.\"O .I ptr
.\"O is NULL, then the call is equivalent to
.\"O .IR malloc(size) ,
.\"O for all values of
.\"O .IR size ;
.\"O if
.\"O .I size
.\"O is equal to zero,
.\"O and
.\"O .I ptr
.\"O is not NULL, then the call is equivalent to
.\"O .IR free(ptr) .
.I size
¤¬¤É¤ÎÃͤǤ¢¤Ã¤Æ¤â¡¢
.I ptr
¤¬ NULL ¤Î¾ì¹ç¤Ë¤Ï
.I malloc(size)
¤ÈÅù²Á¤Ç¤¢¤ë¡£
.I size
¤¬ 0 ¤Ç
.I ptr
¤¬ NULL ¤Ç¤Ê¤¤¾ì¹ç¤Ë¤Ï¡¢
.I free(ptr)
¤ÈÅù²Á¤Ç¤¢¤ë¡£
.\"O Unless
.\"O .I ptr
.\"O is NULL, it must have been returned by an earlier call to
.\"O .BR malloc (),
.\"O .BR calloc ()
.\"O or
.\"O .BR realloc ().
.I ptr
¤¬ NULL °Ê³°¤Î¾ì¹ç¡¢
.I ptr
¤Ï°ÊÁ°¤Ë¸Æ¤Ó½Ð¤µ¤ì¤¿
.BR malloc (),
.BR calloc (),
.BR realloc ()
¤Î¤¤¤º¤ì¤«¤¬ÊÖ¤·¤¿ÃͤǤʤ±¤ì¤Ð¤Ê¤é¤Ê¤¤¡£
.\"O If the area pointed to was moved, a
.\"O .I free(ptr)
.\"O is done.
.I ptr
¤¬»Ø¤¹Îΰ褬°ÜÆ°¤µ¤ì¤Æ¤¤¤¿¾ì¹ç¤Ï
.I free(ptr)
¤¬¼Â¹Ô¤µ¤ì¤ë¡£
.\"O .SH "RETURN VALUE"
.SH ÊÖ¤êÃÍ
.\"O For
.\"O .BR calloc ()
.\"O and
.\"O .BR malloc (),
.\"O return a pointer to the allocated memory, which is suitably
.\"O aligned for any kind of variable.
.\"O On error, these functions return NULL.
.\"O NULL may also be returned by a successful call to
.\"O .BR malloc ()
.\"O with a
.\"O .I size
.\"O of zero,
.\"O or by a successful call to
.\"O .BR calloc ()
.\"O with
.\"O .I nmemb
.\"O or
.\"O .I size
.\"O equal to zero.
.BR calloc ()
¤È
.BR malloc ()
¤Ï¡¢³ä¤êÅö¤Æ¤é¤ì¤¿¥á¥â¥ê¤Ø¤Î¥Ý¥¤¥ó¥¿¤òÊÖ¤¹¡£
³ä¤êÅö¤Æ¤é¤ì¤¿¥á¥â¥ê¤Ï¡¢¤¢¤é¤æ¤ë¼ïÎà¤ÎÊÑ¿ô¤ËÂбþ¤Ç¤­¤ë¤è¤¦¤Ë
¥¢¥é¥¤¥ó¥á¥ó¥È¤µ¤ì¤Æ¤¤¤ë¡£
¥¨¥é¡¼¤Î¾ì¹ç¡¢¤³¤ì¤é¤Î´Ø¿ô¤Ï NULL ¤òÊÖ¤¹¡£
.I size
¤¬ 0 ¤Ç¸Æ¤Ó½Ð¤·¤¿
.BR malloc ()
¤ä¡¢
.I nmemb
¤«
.I size
¤¬ 0 ¤Ç¸Æ¤Ó½Ð¤·¤¿
.BR calloc ()
¤¬À®¸ù¤·¤¿¾ì¹ç¤Ë¤â NULL ¤¬ÊÖ¤µ¤ì¤ë¡£
.PP
.\"O .BR free ()
.\"O returns no value.
.BR free ()
¤ÏÃͤòÊÖ¤µ¤Ê¤¤¡£
.PP
.\"O .BR realloc ()
.\"O returns a pointer to the newly allocated memory, which is suitably
.\"O aligned for any kind of variable and may be different from
.\"O .IR ptr ,
.\"O or NULL if the request fails.
.\"O If
.\"O .I size
.\"O was equal to 0, either NULL or a pointer suitable to be passed to
.\"O .BR free ()
.\"O is returned.
.\"O If
.\"O .BR realloc ()
.\"O fails the original block is left untouched; it is not freed or moved.
.BR realloc ()
¤Ï¿·¤¿¤Ë³ä¤êÅö¤Æ¤é¤ì¤¿¥á¥â¥ê¤Ø¤Î¥Ý¥¤¥ó¥¿¤òÊÖ¤¹¡£
¤³¤ì¤Ï¤¢¤é¤æ¤ë¼ïÎà¤ÎÊÑ¿ô¤ËÂбþ¤Ç¤­¤ë¤è¤¦¤Ë¥¢¥é¥¤¥ó¥á¥ó¥È¤µ¤ì¤Æ¤ª¤ê¡¢
.I ptr
¤È¤Ï°Û¤Ê¤ë¤³¤È¤â¤¢¤ë¡£
³ä¤êÅö¤ÆÍ×µá¤Ë¼ºÇÔ¤·¤¿¾ì¹ç¤Ï NULL ¤¬Ê֤롣
.I size
¤¬ 0 ¤Î¾ì¹ç¤Ë¤Ï¡¢NULL ¤â¤·¤¯¤Ï
.BR free ()
¤ËÅϤ¹¤³¤È¤¬¤Ç¤­¤ë¥Ý¥¤¥ó¥¿¤¬Ê֤롣
.BR realloc ()
¤¬¼ºÇÔ¤·¤¿¾ì¹ç¤Ë¤Ï¡¢¸µ¤Î¥Ö¥í¥Ã¥¯¤ÏÊѹ¹¤µ¤ì¤Ê¤¤¡£
¤Ä¤Þ¤ê¡¢²òÊü¤µ¤ì¤¿¤ê°ÜÆ°¤µ¤ì¤¿¤ê¤Ï¤·¤Ê¤¤¡£
.\"O .SH "CONFORMING TO"
.SH ½àµò
C89, C99.
.\"O .SH NOTES
.SH Ãí°Õ
.\"O Normally,
.\"O .BR malloc ()
.\"O allocates memory from the heap, and adjusts the size of the heap
.\"O as required, using
.\"O .BR sbrk (2).
Ä̾
.BR malloc ()
¤Ï¡¢¥Ò¡¼¥×¤«¤é¥á¥â¥ê¤ò³ä¤êÅö¤Æ¡¢É¬Íפ˱þ¤¸¤Æ¥Ò¡¼¥×¤Î¥µ¥¤¥º¤ò
.BR sbrk (2)
¤ò»È¤Ã¤ÆÄ´À᤹¤ë¡£
.\"O When allocating blocks of memory larger than
.\"O .B MMAP_THRESHOLD
.\"O bytes, the glibc
.\"O .BR malloc ()
.\"O implementation allocates the memory as a private anonymous mapping using
.\"O .BR mmap (2).
.\"O .B MMAP_THRESHOLD
.\"O is 128 kB by default, but is adjustable using
.\"O .BR mallopt (3).
.B MMAP_THRESHOLD
¥Ð¥¤¥È¤è¤ê¤âÂ礭¤Ê¥á¥â¥ê¥Ö¥í¥Ã¥¯¤ò³ä¤êÅö¤Æ¤ë¾ì¹ç¡¢
glibc ¤Î
.BR malloc ()
¼ÂÁõ¤Ï
.BR mmap (2)
¤ò»È¤Ã¤Æ¥×¥é¥¤¥Ù¡¼¥È¤Ê̵̾¥Þ¥Ã¥Ô¥ó¥° (anonymous mapping) ¤È¤·¤Æ
¥á¥â¥ê¤ò³ä¤êÅö¤Æ¤ë¡£
¥Ç¥Õ¥©¥ë¥È¤Ç¤Ï
.B MMAP_THRESHOLD
¤Ï 128 kB ¤À¤¬¡¢
.BR mallopt (3)
¤ò»È¤Ã¤ÆÄ´À°¤Ç¤­¤ë¡£
.\" FIXME . there is no mallopt(3) man page yet.
.\"O Allocations performed using
.\"O .BR mmap (2)
.\"O are unaffected by the
.\"O .B RLIMIT_DATA
.\"O resource limit (see
.\"O .BR getrlimit (2)).
.BR mmap (2)
¤ò»È¤Ã¤Æ¹Ô¤ï¤ì¤¿¥á¥â¥ê³ä¤êÅö¤Æ¤Ï
.B RLIMIT_DATA
¥ê¥½¡¼¥¹¾å¸Â¤Î±Æ¶Á¤ò¼õ¤±¤Ê¤¤
.RB ( getrlimit (2)
»²¾È)¡£

.\"O The Unix98 standard requires
.\"O .BR malloc (),
.\"O .BR calloc (),
.\"O and
.\"O .BR realloc ()
.\"O to set
.\"O .I errno
.\"O to
.\"O .B ENOMEM
.\"O upon failure.
.\"O Glibc assumes that this is done
.\"O (and the glibc versions of these routines do this); if you
.\"O use a private malloc implementation that does not set
.\"O .IR errno ,
.\"O then certain library routines may fail without having
.\"O a reason in
.\"O .IR errno .
Unix98 ɸ½à¤Ç¤Ï¡¢
.BR malloc (),
.BR calloc (),
.BR realloc ()
¤Ï¼Â¹Ô¤Ë¼ºÇÔ¤·¤¿¤È¤­¤Ë
.I errno
¤ò
.B ENOMEM
¤ËÀßÄꤹ¤ë¤³¤È¤Ë¤Ê¤Ã¤Æ¤¤¤ë¡£
Glibc ¤Ç¤Ï¤³¤ì¤¬¼é¤é¤ì¤Æ¤¤¤ë¤³¤È¤ò²¾Äꤷ¤Æ¤¤¤ë
(¤Þ¤¿¤³¤ì¤é¤Î¥ë¡¼¥Á¥ó¤Î glibc ¥Ð¡¼¥¸¥ç¥ó¤Ï¤³¤Î¤³¤È¤ò¼é¤Ã¤Æ¤¤¤ë)¡£
¸Ä¿ÍŪ¤ËÊ̤Πmalloc ¤Î¼ÂÁõ¤ò»È¤Ã¤Æ¤¤¤Æ¡¢¤½¤Î malloc ¤¬
.I errno
¤òÀßÄꤷ¤Ê¤¤¾ì¹ç¤Ë¤Ï¡¢¼ºÇÔ¤·¤¿ºÝ¤Ë
.I errno
¤Ë¥¨¥é¡¼¤ÎÍýͳ¤òÀßÄꤷ¤Ê¤¤¥é¥¤¥Ö¥é¥ê¥ë¡¼¥Á¥ó¤¬¤¢¤ë¤«¤â¤·¤ì¤Ê¤¤¡£
.LP
.\"O Crashes in
.\"O .BR malloc (),
.\"O .BR calloc (),
.\"O .BR realloc (),
.\"O or
.\"O .BR free ()
.\"O are almost always related to heap corruption, such as overflowing
.\"O an allocated chunk or freeing the same pointer twice.
.BR malloc (),
.BR calloc (),
.BR realloc (),
.BR free ()
¤Ë¤ª¤±¤ë»ö¸Î¤Ï¡¢
¤Û¤È¤ó¤É¤Î¾ì¹ç¤Ï¥Ò¡¼¥×¤ÎÇ˲õ (corruption) ¤¬¸¶°ø¤Ç¤¢¤ë¡£
Î㤨¤Ð¡¢³ä¤êÅö¤Æ¤é¤ì¤¿Îΰè¤ò¥ª¡¼¥Ð¡¼¥Õ¥í¡¼¤¹¤ë¡¢
Ʊ¤¸¥Ý¥¤¥ó¥¿¤ËÆóÅÙ free ¤¹¤ë¡¢¤Ê¤É¤¬¤³¤ì¤Ë¤¢¤¿¤ë¡£
.PP
.\"O Recent versions of Linux libc (later than 5.4.23) and glibc (2.x)
.\"O include a
.\"O .BR malloc ()
.\"O implementation which is tunable via environment variables.
.\"O When
.\"O .B MALLOC_CHECK_
.\"O is set, a special (less efficient) implementation is used which
.\"O is designed to be tolerant against simple errors, such as double
.\"O calls of
.\"O .BR free ()
.\"O with the same argument, or overruns of a single byte (off-by-one
.\"O bugs).
.\"O Not all such errors can be protected against, however, and
.\"O memory leaks can result.
ºÇ¶á¤Î¥Ð¡¼¥¸¥ç¥ó¤Î Linux libc (5.4.23 °Ê¹ß) ¤È glibc (2.x) ¤Ç¤Ï¡¢
.BR malloc ()
¤ÎÆ°ºî¤ò´Ä¶­ÊÑ¿ô¤Ë¤è¤Ã¤ÆÀ©¸æ¤Ç¤­¤ë¤è¤¦¤Ê¼ÂÁõ¤¬¤µ¤ì¤Æ¤¤¤ë¡£
.B MALLOC_CHECK_
¤¬ÀßÄꤵ¤ì¤Æ¤¤¤ë¤È¡¢Æüì¤Ê¼ÂÁõ¤¬ÍѤ¤¤é¤ì¡¢
ñ½ã¤Ê¥¨¥é¡¼¤Ë¤ÏÂѤ¨¤ë¤³¤È¤¬¤Ç¤­¤ë¤è¤¦¤Ë¤Ê¤ë (¸úΨ¤Ï°­¤¯¤Ê¤ë)¡£Î㤨¤Ð¡¢
.BR free ()
¤òƱ¤¸°ú¤­¿ô¤ÇÆóÅٸƤӽФ·¤Æ¤·¤Þ¤¦¡¢
1 ¥Ð¥¤¥È¤À¤±¹Ô¤­¤¹¤®¤Æ¤·¤Þ¤¦ (off-by-one ¥Ð¥°) ¤Ê¤É¤¬¤³¤ì¤ËÅö¤¿¤ë¡£
¤·¤«¤·¡¢¤³¤ì¤é¤Î¥¨¥é¡¼¤ÎÁ´¤Æ¤òËɤ°¤³¤È¤¬¤Ç¤­¤ë¤ï¤±¤Ç¤Ï¤Ê¤¯¡¢
¤½¤Î¾ì¹ç¤Ë¤Ï¥á¥â¥ê¥ê¡¼¥¯¤¬µ¯¤³¤Ã¤Æ¤·¤Þ¤¦¡£
.\"O If
.\"O .B MALLOC_CHECK_
.\"O is set to 0, any detected heap corruption is silently ignored;
.\"O if set to 1, a diagnostic is printed on \fIstderr\fP;
.\"O if set to 2,
.\"O .BR abort (3)
.\"O is called immediately;
.\"O if set to 3, a diagnostic message is printed on \fIstderr\fP
.\"O and the program is aborted.
.\"O Using a nonzero
.\"O .B MALLOC_CHECK_
.\"O value can be useful because otherwise
.\"O a crash may happen much later, and the true cause for the problem
.\"O is then very hard to track down.
.B MALLOC_CHECK_
¤¬ 0 ¤Ë¥»¥Ã¥È¤µ¤ì¤Æ¤¤¤ë¤È¡¢¥Ò¡¼¥×¤ÎÇ˲õ¤òÌۤäÆ̵»ë¤¹¤ë¡£
1 ¤Ë¥»¥Ã¥È¤µ¤ì¤Æ¤¤¤ë¤È¡¢¿ÇÃÇ¥á¥Ã¥»¡¼¥¸¤¬É¸½à¥¨¥é¡¼½ÐÎϤËɽ¼¨¤µ¤ì¤ë¡£
2 ¤Ë¥»¥Ã¥È¤µ¤ì¤Æ¤¤¤ë¤È¡¢¤¿¤À¤Á¤Ë
.BR abort (3)
¤¬¸Æ¤Ó½Ð¤µ¤ì¤ë¡£
3 ¤Ë¥»¥Ã¥È¤µ¤ì¤Æ¤¤¤ë¤È¡¢¿ÇÃÇ¥á¥Ã¥»¡¼¥¸¤¬É¸½à¥¨¥é¡¼½ÐÎϤËɽ¼¨¤µ¤ì¡¢
¥×¥í¥°¥é¥à¤Ï¶¯À©½ªÎ» (abort) ¤µ¤ì¤ë¡£
.B MALLOC_CHECK_
¤Ë 0 °Ê³°¤ÎÃͤò¥»¥Ã¥È¤·¤ÆÌò¤ËΩ¤Ä¾õ¶·¤È¤·¤Æ¤Ï¡¢
¼ÂºÝ¤Î¥×¥í¥»¥¹¤Î¥¯¥é¥Ã¥·¥å¤¬¤º¤Ã¤È¸å¤Ëµ¯¤³¤ê¡¢
ËÜÅö¤Î¸¶°ø¤òõ¤·½Ð¤¹¤Î¤¬Èó¾ï¤Ëº¤Æñ¤Ê¾ì¹ç¤Ê¤É¤¬µó¤²¤é¤ì¤ë¤À¤í¤¦¡£
.\"O .SH BUGS
.SH ¥Ð¥°
.\"O By default, Linux follows an optimistic memory allocation strategy.
¥Ç¥Õ¥©¥ë¥È¤Ç¤Ï¡¢Linux ¤Ï³Ú´ÑŪ¥á¥â¥êÇÛÃÖÀïά¤òÍѤ¤¤Æ¤¤¤ë¡£
.\"O This means that when
.\"O .BR malloc ()
.\"O returns non-NULL there is no guarantee that the memory really
.\"O is available.
.\"O This is a really bad bug.
.\"O In case it turns out that the system is out of memory,
.\"O one or more processes will be killed by the infamous OOM killer.
¤Ä¤Þ¤ê¡¢
.BR malloc ()
¤¬ NULL ¤Ç¤Ê¤¤ÃͤòÊÖ¤·¤Æ¤â¡¢¤½¤Î¥á¥â¥ê¤¬¼ÂºÝ¤ËÍøÍѲÄǽ¤Ç¤¢¤ë¤³¤È¤¬
Êݾڤµ¤ì¤Ê¤¤¡£¤³¤ì¤ÏËÜÅö¤Ë¤Þ¤º¤¤¥Ð¥°¤Ç¤¢¤ë¡£
¥·¥¹¥Æ¥à¤¬¥á¥â¥êÉÔ­¾õÂ֤ˤʤ俤Ȥ­¡¢°­Ì¾¹â¤¤¥á¥â¥êÉÔ­²ò·è´ï (OOM killer)
¤Ë¤è¤Ã¤Æ°ì¤Ä¤Þ¤¿¤ÏÊ£¿ô¤Î¥×¥í¥»¥¹¤¬ºï½ü¤µ¤ì¤ë¡£
.\"O In case Linux is employed under circumstances where it would be
.\"O less desirable to suddenly lose some randomly picked processes,
.\"O and moreover the kernel version is sufficiently recent,
.\"O one can switch off this overcommitting behavior using a command like:
ÆÍÁ³¤¢¤ë¥×¥í¥»¥¹¤¬ºï½ü¤µ¤ì¤ë¤Î¤¬Ë¾¤Þ¤·¤¯¤Ê¤¤¾õ¶·¤Ç»ÈÍѤµ¤ì¤Æ¤¤¤Æ¡¢
¤·¤«¤â¥«¡¼¥Í¥ë¤Î¥Ð¡¼¥¸¥ç¥ó¤¬½½Ê¬¤ËºÇ¶á¤Î¤â¤Î¤Ç¤¢¤ì¤Ð¡¢¤³¤Î¥á¥â¥ê¤ò
³ä¤êÅö¤Æ²á¤®¤ëÆ°ºî (overcommitting behavior) ¤ò°Ê²¼¤Î¥³¥Þ¥ó¥É¤Ç
̵¸ú¤Ë¤Ç¤­¤ë¡£
.in +4n
.sp
.nf
.RB "#" " echo 2 > /proc/sys/vm/overcommit_memory"

.fi
.in
.\"O See also the kernel Documentation directory, files
.\"O .I vm/overcommit-accounting
.\"O and
.\"O .IR sysctl/vm.txt .
¥«¡¼¥Í¥ë¤ÎÉÕ°ʸ½ñ¤Î
.I vm/overcommit-accounting
¤È
.I sysctl/vm.txt
¤â»²¾È¤Î¤³¤È¡£
.\"O .SH "SEE ALSO"
.SH ´ØÏ¢¹àÌÜ
.BR brk (2),
.BR posix_memalign (3)
.\" .BR mallopt (3),
.BR mmap (2),
.BR alloca (3),