Copyright (C) 2001 Andries Brouwer <firstname.lastname@example.org> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the L...
NAMEgetpagesize - get memory page size
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
- 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
DESCRIPTIONThe 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 TOSVr4, 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.
NOTESPortable 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.