Manpages - getpagesize.2

getpagesize - get memory page size

  #include <unistd.h>

  int getpagesize(void);

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

*getpagesize*():

      Since glibc 2.20:
          _DEFAULT_SOURCE || ! (_POSIX_C_SOURCE >= 200112L)
      Glibc 2.12 to 2.19:
          _BSD_SOURCE || ! (_POSIX_C_SOURCE >= 200112L)
      Before glibc 2.12:
          _BSD_SOURCE || _XOPEN_SOURCE >= 500

The 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).

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 *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.

*mmap*(2), *sysconf*(3)

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