man2/mincore.2

   1 .\" Copyright (C) 2001 Bert Hubert <ahu@ds9a.nl>
   2 .\" and Copyright (C) 2007 Michael Kerrisk <mtk.manpages@gmail.com>
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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 2017-09-15 "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 .PP
  42 .BI "int mincore(void *" addr ", size_t " length ", unsigned char *" vec );
  43 .PP
  44 .in -4n
  45 Feature Test Macro Requirements for glibc (see
  46 .BR feature_test_macros (7)):
  47 .in
  48 .PP
  49 .BR mincore ():
  50     Since glibc 2.19:
  51         _DEFAULT_SOURCE
  52     Glibc 2.19 and earlier:
  53         _BSD_SOURCE || _SVID_SOURCE
  54 .SH DESCRIPTION
  55 .BR mincore ()
  56 returns a vector that indicates whether pages
  57 of the calling process's virtual memory are resident in core (RAM),
  58 and so will not cause a disk access (page fault) if referenced.
  59 The kernel returns residency information about the pages
  60 starting at the address
  61 .IR addr ,
  62 and continuing for
  63 .I length
  64 bytes.
  65 .PP
  66 The
  67 .I addr
  68 argument must be a multiple of the system page size.
  69 The
  70 .I length
  71 argument need not be a multiple of the page size,
  72 but since residency information is returned for whole pages,
  73 .I length
  74 is effectively rounded up to the next multiple of the page size.
  75 One may obtain the page size
  76 .RB ( PAGE_SIZE )
  77 using
  78 .IR sysconf(_SC_PAGESIZE) .
  79 .PP
  80 The
  81 .I vec
  82 argument must point to an array containing at least
  83 .I "(length+PAGE_SIZE\-1) / PAGE_SIZE"
  84 bytes.
  85 On return,
  86 the least significant bit of each byte will be set if
  87 the corresponding page is currently resident in memory,
  88 and be clear otherwise.
  89 (The settings of the other bits in each byte are undefined;
  90 these bits are reserved for possible later use.)
  91 Of course the information returned in
  92 .I vec
  93 is only a snapshot: pages that are not
  94 locked in memory can come and go at any moment, and the contents of
  95 .I vec
  96 may already be stale by the time this call returns.
  97 .SH RETURN VALUE
  98 On success,
  99 .BR mincore ()
 100 returns zero.
 101 On error, \-1 is returned, and
 102 .I errno
 103 is set appropriately.
 104 .SH ERRORS
 105 .B EAGAIN
 106 kernel is temporarily out of resources.
 107 .TP
 108 .B EFAULT
 109 .I vec
 110 points to an invalid address.
 111 .TP
 112 .B EINVAL
 113 .I addr
 114 is not a multiple of the page size.
 115 .TP
 116 .B ENOMEM
 117 .I length
 118 is greater than
 119 .RI ( TASK_SIZE " \- " addr ).
 120 (This could occur if a negative value is specified for
 121 .IR length ,
 122 since that value will be interpreted as a large
 123 unsigned integer.)
 124 In Linux 2.6.11 and earlier, the error
 125 .B EINVAL
 126 was returned for this condition.
 127 .TP
 128 .B ENOMEM
 129 .I addr
 130 to
 131 .I addr
 132 +
 133 .I length
 134 contained unmapped memory.
 135 .SH VERSIONS
 136 Available since Linux 2.3.99pre1 and glibc 2.2.
 137 .SH CONFORMING TO
 138 .BR mincore ()
 139 is not specified in POSIX.1,
 140 and it is not available on all UNIX implementations.
 141 .\" It is on at least NetBSD, FreeBSD, OpenBSD, Solaris 8,
 142 .\" AIX 5.1, SunOS 4.1
 143 .\" .SH HISTORY
 144 .\" The
 145 .\" .BR mincore ()
 146 .\" function first appeared in 4.4BSD.
 147 .SH BUGS
 148 Before kernel 2.6.21,
 149 .BR mincore ()
 150 did not return correct information for
 151 .B MAP_PRIVATE
 152 mappings, or for nonlinear mappings (established using
 153 .BR remap_file_pages (2)).
 154 .\" Linux (up to now, 2.6.5),
 155 .\" .B mincore
 156 .\" does not return correct information for MAP_PRIVATE mappings:
 157 .\" for a MAP_PRIVATE file mapping,
 158 .\" .B mincore
 159 .\" returns the residency of the file pages, rather than any
 160 .\" modified process-private pages that have been copied on write;
 161 .\" for a MAP_PRIVATE mapping of
 162 .\" .IR /dev/zero ,
 163 .\" .B mincore
 164 .\" always reports pages as nonresident;
 165 .\" and for a MAP_PRIVATE, MAP_ANONYMOUS mapping,
 166 .\" .B mincore
 167 .\" always fails with the error
 168 .\" .BR ENOMEM .
 169 .SH SEE ALSO
 170 .BR fincore (1),
 171 .BR madvise (2),
 172 .BR mlock (2),
 173 .BR mmap (2),
 174 .BR posix_fadvise (2),
 175 .BR posix_madvise (3)