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@gmail.com>
   5 .\"
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  25 .\"
  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@gmail.com>
  29 .\" Modified, 30 Apr 2004, Michael Kerrisk <mtk.manpages@gmail.com>
  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 2007-07-26 "Linux" "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 .sp
  44 .in -4n
  45 Feature Test Macro Requirements for glibc (see
  46 .BR feature_test_macros (7)):
  47 .in
  48 .sp
  49 .BR mincore ():
  50 _BSD_SOURCE || _SVID_SOURCE
  51 .SH DESCRIPTION
  52 .BR mincore ()
  53 returns a vector that indicates whether pages
  54 of the calling process's virtual memory are resident in core (RAM),
  55 and so will not cause a disk access (page fault) if referenced.
  56 The kernel returns residency information about the pages
  57 starting at the address
  58 .IR start ,
  59 and continuing for
  60 .I length
  61 bytes.
  62
  63 The
  64 .I start
  65 argument must be a multiple of the system page size.
  66 The
  67 .I length
  68 argument need not be a multiple of the page size,
  69 but since residency information is returned for whole pages,
  70 .I length
  71 is effectively rounded up to the next multiple of the page size.
  72 One may obtain the page size (PAGE_SIZE) using
  73 .IR sysconf(_SC_PAGESIZE) .
  74
  75 The
  76 .I vec
  77 argument must point to an array containing at least
  78 (length+PAGE_SIZE-1) / PAGE_SIZE bytes.
  79 On return,
  80 the least significant bit of each byte will be set if
  81 the corresponding page is currently resident in memory,
  82 and be clear otherwise.
  83 (The settings of the other bits in each byte are undefined;
  84 these bits are reserved for possible later use.)
  85 Of course the information returned in
  86 .I vec
  87 is only a snapshot: pages that are not
  88 locked in memory can come and go at any moment, and the contents of
  89 .I vec
  90 may already be stale by the time this call returns.
  91 .SH "RETURN VALUE"
  92 On success,
  93 .BR mincore ()
  94 returns zero.
  95 On error, \-1 is returned, and
  96 .I errno
  97 is set appropriately.
  98 .SH ERRORS
  99 .B EAGAIN
 100 kernel is temporarily out of resources.
 101 .TP
 102 .B EFAULT
 103 .I vec
 104 points to an invalid address.
 105 .TP
 106 .B EINVAL
 107 .I start
 108 is not a multiple of the page size.
 109 .TP
 110 .B ENOMEM
 111 .I length
 112 is greater than
 113 .RI ( TASK_SIZE " \- " start ).
 114 (This could occur if a negative value is specified for
 115 .IR length ,
 116 since that value will be interpreted as a large
 117 unsigned integer.)
 118 In Linux 2.6.11 and earlier, the error
 119 .B EINVAL
 120 was returned for this condition.
 121 .TP
 122 .B ENOMEM
 123 .I start
 124 to
 125 .I start
 126 +
 127 .I length
 128 contained unmapped memory.
 129 .SH VERSIONS
 130 Available since Linux 2.3.99pre1 and glibc 2.2.
 131 .SH "CONFORMING TO"
 132 .BR mincore ()
 133 is not specified in POSIX.1-2001,
 134 and it is not available on all Unix implementations.
 135 .\" It is on at least NetBSD, FreeBSD, OpenBSD, Solaris 8,
 136 .\" AIX 5.1, SunOS 4.1
 137 .\" .SH HISTORY
 138 .\" The
 139 .\" .BR mincore ()
 140 .\" function first appeared in 4.4BSD.
 141 .SH BUGS
 142 Before kernel 2.6.21,
 143 .BR mincore ()
 144 did not return correct information for
 145 .B MAP_PRIVATE
 146 mappings, or for non-linear mappings (established using
 147 .BR remap_file_pages (2)).
 148 .\" Linux (up to now, 2.6.5),
 149 .\" .B mincore
 150 .\" does not return correct information for MAP_PRIVATE mappings:
 151 .\" for a MAP_PRIVATE file mapping,
 152 .\" .B mincore
 153 .\" returns the residency of the file pages, rather than any
 154 .\" modified process-private pages that have been copied on write;
 155 .\" for a MAP_PRIVATE mapping of
 156 .\" .IR /dev/zero ,
 157 .\" .B mincore
 158 .\" always reports pages as non-resident;
 159 .\" and for a MAP_PRIVATE, MAP_ANONYMOUS mapping,
 160 .\" .B mincore
 161 .\" always fails with the error
 162 .\" .BR ENOMEM .
 163 .SH "SEE ALSO"
 164 .BR mlock (2),
 165 .BR mmap (2)