man2/getpagesize.2

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  25 .TH GETPAGESIZE 2 2017-09-15 "Linux" "Linux Programmer's Manual"
  26 .SH NAME
  27 getpagesize \- get memory page size
  28 .SH SYNOPSIS
  29 .B #include <unistd.h>
  30 .PP
  31 .B int getpagesize(void);
  32 .PP
  33 .in -4n
  34 Feature Test Macro Requirements for glibc (see
  35 .BR feature_test_macros (7)):
  36 .in
  37 .PP
  38 .BR getpagesize ():
  39 .ad l
  40 .RS 4
  41 .PD 0
  42 .TP 4
  43 Since glibc 2.19:
  44 .nf
  45 _DEFAULT_SOURCE || ! (_POSIX_C_SOURCE\ >=\ 200112L)
  46 .TP 4
  47 .fi
  48 From glibc 2.12 to 2.19:
  49 .nf
  50 _BSD_SOURCE || ! (_POSIX_C_SOURCE\ >=\ 200112L)
  51 .TP 4
  52 .fi
  53 Before glibc 2.12:
  54 _BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
  55 .\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  56 .PD
  57 .RE
  58 .ad b
  59 .SH DESCRIPTION
  60 The function
  61 .BR getpagesize ()
  62 returns the number of bytes in a memory page,
  63 where "page" is a fixed-length block,
  64 the unit for memory allocation and file mapping performed by
  65 .BR mmap (2).
  66 .\" .SH HISTORY
  67 .\" This call first appeared in 4.2BSD.
  68 .SH CONFORMING TO
  69 SVr4, 4.4BSD, SUSv2.
  70 In SUSv2 the
  71 .BR getpagesize ()
  72 call is labeled LEGACY, and in POSIX.1-2001
  73 it has been dropped;
  74 HP-UX does not have this call.
  75 .SH NOTES
  76 Portable applications should employ
  77 .I sysconf(_SC_PAGESIZE)
  78 instead of
  79 .BR getpagesize ():
  80 .PP
  81 .in +4n
  82 .EX
  83 #include <unistd.h>
  84 long sz = sysconf(_SC_PAGESIZE);
  85 .EE
  86 .in
  87 .PP
  88 (Most systems allow the synonym
  89 .B _SC_PAGE_SIZE
  90 for
  91 .BR _SC_PAGESIZE .)
  92 .PP
  93 Whether
  94 .BR getpagesize ()
  95 is present as a Linux system call depends on the architecture.
  96 If it is, it returns the kernel symbol
  97 .BR PAGE_SIZE ,
  98 whose value depends on the architecture and machine model.
  99 Generally, one uses binaries that are dependent on the architecture but not
 100 on the machine model, in order to have a single binary
 101 distribution per architecture.
 102 This means that a user program
 103 should not find
 104 .B PAGE_SIZE
 105 at compile time from a header file,
 106 but use an actual system call, at least for those architectures
 107 (like sun4) where this dependency exists.
 108 Here glibc 2.0 fails because its
 109 .BR getpagesize ()
 110 returns a statically derived value, and does not use a system call.
 111 Things are OK in glibc 2.1.
 112 .SH SEE ALSO
 113 .BR mmap (2),
 114 .BR sysconf (3)