getpagesize - get memory page size


#include <unistd.h>

int getpagesize(void);

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

getpagesize(): _BSD_SOURCE || _XOPEN_SOURCE >= 500


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();


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.


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 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)


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