getpagesize(2)



GETPAGESIZE(2)             Linux Programmer's Manual            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 alloca-
       tion 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 archi-
       tecture.   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 4.05 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/.

Linux                             2016-03-15                    GETPAGESIZE(2)

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