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GETPAGESIZE(3) Library Functions Manual GETPAGESIZE(3)

getpagesize —
get system page size

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

This interface is obsoleted by sysconf(3). Use sysconf(_SC_PAGESIZE).
The getpagesize() function returns the number of bytes in a page. Page granularity is the granularity of many of the memory management calls.
The page size is a system page size and may not be the same as the underlying hardware page size.

pagesize(1), sbrk(2), sysconf(3)

The getpagesize() function call appeared in 4.2BSD.
June 5, 2013 OpenBSD-current