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 2.12:
_BSD_SOURCE ||
!(_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
Before glibc 2.12:
_BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
DESCRIPTION
The function getpagesize() returns the number of bytes in a page, where
a "page" is the thing used where it says in the description of mmap(2)
that files are mapped in page-sized units.
The size of the kind of pages that mmap(2) uses, is found using
#include <unistd.h>
long sz = sysconf(_SC_PAGESIZE);
(most systems allow the synonym _SC_PAGE_SIZE for _SC_PAGESIZE), or
#include <unistd.h>
int sz = getpagesize();
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. Portable applications should employ sysconf(_SC_PAGESIZE)
instead of this call.
NOTES
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 libc4, libc5, glibc 2.0 fail because their 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 3.27 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2010-09-20 GETPAGESIZE(2)
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