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getpagesize(2)


NAME

   getpagesize - get memory page size

SYNOPSIS

   #include <unistd.h>

   int getpagesize(void);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

   getpagesize():
       Since glibc 2.19:
           _DEFAULT_SOURCE || ! (_POSIX_C_SOURCE >= 200112L)
       From glibc 2.12 to 2.19:
           _BSD_SOURCE || ! (_POSIX_C_SOURCE >= 200112L)
       Before glibc 2.12:
           _BSD_SOURCE || _XOPEN_SOURCE >= 500

DESCRIPTION

   The  function  getpagesize()  returns  the  number of bytes in a memory
   page, where "page"  is  a  fixed-length  block,  the  unit  for  memory
   allocation and file mapping performed by mmap(2).

CONFORMING TO

   SVr4,  4.4BSD,  SUSv2.   In  SUSv2  the  getpagesize()  call is labeled
   LEGACY, and in POSIX.1-2001 it has been dropped; HP-UX  does  not  have
   this call.

NOTES

   Portable  applications  should  employ sysconf(_SC_PAGESIZE) instead of
   getpagesize():

       #include <unistd.h>
       long sz = sysconf(_SC_PAGESIZE);

   (Most systems allow the synonym _SC_PAGE_SIZE for _SC_PAGESIZE.)

   Whether getpagesize() is present as a Linux system call depends on  the
   architecture.   If it is, it returns the kernel symbol PAGE_SIZE, whose
   value depends on the architecture and machine  model.   Generally,  one
   uses  binaries  that  are  dependent on the architecture but not on the
   machine model, in order  to  have  a  single  binary  distribution  per
   architecture.  This means that a user program should not find PAGE_SIZE
   at compile time from a header file, but use an actual system  call,  at
   least for those architectures (like sun4) where this dependency exists.
   Here glibc 2.0 fails because its  getpagesize()  returns  a  statically
   derived  value, and does not use a system call.  Things are OK in glibc
   2.1.

SEE ALSO

   mmap(2), sysconf(3)

COLOPHON

   This page is part of release 4.09 of the Linux  man-pages  project.   A
   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at
   https://www.kernel.org/doc/man-pages/.



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