man2/mincore.2

   1 .\" Hey Emacs! This file is -*- nroff -*- source.
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   3 .\" Copyright (C) 2001 Bert Hubert <ahu@ds9a.nl>
   4 .\" and Copyright (C) 2007 Michael Kerrisk <mtk-manpages@gmx.net>
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  26 .\" Created Sun Jun 3 17:23:32 2001 by bert hubert <ahu@ds9a.nl>
  27 .\" Slightly adapted, following comments by Hugh Dickins, aeb, 2001-06-04.
  28 .\" Modified, 20 May 2003, Michael Kerrisk <mtk-manpages@gmx.net>
  29 .\" Modified, 30 Apr 2004, Michael Kerrisk <mtk-manpages@gmx.net>
  30 .\" 2005-04-05 mtk, Fixed error descriptions
  31 .\"     after message from <gordon.jin@intel.com>
  32 .\" 2007-01-08 mtk, rewrote various parts
  33 .\"
  34 .TH MINCORE 2 2007-01-08 "Linux 2.6.5" "Linux Programmer's Manual"
  35 .SH NAME
  36 mincore \- determine whether pages are resident in memory
  37 .SH SYNOPSIS
  38 .B #include <unistd.h>
  39 .br
  40 .B #include <sys/mman.h>
  41 .sp
  42 .BI "int mincore(void *" start ", size_t " length ", unsigned char *" vec );
  43 .SH DESCRIPTION
  44 .BR mincore ()
  45 returns a vector that indicates whether pages
  46 of the calling process's virtual memory are resident in core (RAM),
  47 and so will not cause a disk access (page fault) if referenced.
  48 The kernel returns residency information about the pages
  49 starting at the address
  50 .IR start ,
  51 and continuing for
  52 .I length
  53 bytes.
  54
  55 The
  56 .I start
  57 argument must be a multiple of the system page size.
  58 The
  59 .I length
  60 argument need not be a multiple of the page size,
  61 but since residency information is returned for whole pages,
  62 .I length
  63 is effectively rounded up to the next multiple of the page size.
  64 One may obtain the page size (PAGE_SIZE) using
  65 .IR sysconf(_SC_PAGESIZE) .
  66
  67 The
  68 .I vec
  69 argument must point to an array containing at least
  70 (length+PAGE_SIZE-1) / PAGE_SIZE bytes.
  71 On return,
  72 the least significant bit of each byte will be set if
  73 the corresponding page is currently resident in memory,
  74 and be clear otherwise.
  75 (The settings of the other bits in each byte are undefined;
  76 these bits are reserved for possible later use.)
  77 Of course the information returned in
  78 .I vec
  79 is only a snapshot: pages that are not
  80 locked in memory can come and go at any moment, and the contents of
  81 .I vec
  82 may already be stale by the time this call returns.
  83 .SH "RETURN VALUE"
  84 On success,
  85 .BR mincore ()
  86 returns zero.
  87 On error, \-1 is returned, and
  88 .I errno
  89 is set appropriately.
  90 .SH ERRORS
  91 .B EAGAIN
  92 kernel is temporarily out of resources.
  93 .TP
  94 .B EFAULT
  95 .I vec
  96 points to an invalid address.
  97 .TP
  98 .B EINVAL
  99 .I start
 100 is not a multiple of the page size.
 101 .TP
 102 .B ENOMEM
 103 .I length
 104 is greater than
 105 .RI ( TASK_SIZE " \- " start ).
 106 (This could occur if a negative value is specified for
 107 .IR length ,
 108 since that value will be interpreted as a large
 109 unsigned integer.)
 110 In Linux 2.6.11 and earlier, the error
 111 .B EINVAL
 112 was returned for this condition.
 113 .TP
 114 .B ENOMEM
 115 .I start
 116 to
 117 .I start
 118 +
 119 .I length
 120 contained unmapped memory.
 121 .SH BUGS
 122 Before kernel 2.6.21,
 123 .BR mincore ()
 124 did not return correct information for
 125 .B MAP_PRIVATE
 126 mappings, or for non-linear mappings (established using
 127 .BR remap_file_pages (2)).
 128 .\" Linux (up to now, 2.6.5),
 129 .\" .B mincore
 130 .\" does not return correct information for MAP_PRIVATE mappings:
 131 .\" for a MAP_PRIVATE file mapping,
 132 .\" .B mincore
 133 .\" returns the residency of the file pages, rather than any
 134 .\" modified process-private pages that have been copied on write;
 135 .\" for a MAP_PRIVATE mapping of
 136 .\" .IR /dev/zero ,
 137 .\" .B mincore
 138 .\" always reports pages as non-resident;
 139 .\" and for a MAP_PRIVATE, MAP_ANONYMOUS mapping,
 140 .\" .B mincore
 141 .\" always fails with the error
 142 .\" .BR ENOMEM .
 143 .SH "CONFORMING TO"
 144 .BR mincore ()
 145 is not specified in POSIX.1-2001,
 146 and it is not available on all Unix implementations.
 147 .\" It is on at least NetBSD, FreeBSD, OpenBSD, Solaris 8,
 148 .\" AIX 5.1, SunOS 4.1
 149 .SH HISTORY
 150 The
 151 .BR mincore ()
 152 function first appeared in 4.4BSD.
 153 .SH AVAILABILITY
 154 Since Linux 2.3.99pre1 and glibc 2.2.
 155 .SH "SEE ALSO"
 156 .BR mlock (2),
 157 .BR mmap (2)