getpagesize(2) -- Linux man page



getpagesize - get memory page size  


#include <unistd.h>

int getpagesize(void);  


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 uses, is found using

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

(where some systems also allow the synonym _SC_PAGE_SIZE for _SC_PAGESIZE), or

#include <unistd.h>
int sz = getpagesize();


This call first appeared in 4.2BSD.  


SVr4, 4.4BSD, SUSv2. In SUSv2 the getpagesize() call is labeled "legacy", and in POSIX 1003.1-2001 it has been dropped. HPUX does not have this call.  


Whether getpagesize() is present as a Linux system call depends on the architecture. If it is, it returns the kernel symbol PAGE_SIZE, which is architecture and machine model dependent. Generally, one uses binaries that are architecture but not machine model dependent, 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 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.  


mmap(2), sysconf(3)