#include <unistd.h>

       int getpagesize(void);

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

           Since glibc 2.12:
               _BSD_SOURCE ||
                   !(_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
           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 alloca-
       tion 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

           #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 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.

       mmap(2), sysconf(3)

       This  page  is  part of release 3.54 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at
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