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RedHat 9 (Linux i386) - man page for munlock (redhat section 2)

MUNLOCK(2)						     Linux Programmer's Manual							MUNLOCK(2)

munlock - reenable paging for some parts of memory
#include <sys/mman.h> int munlock(const void *addr, size_t len);
munlock reenables paging for the memory in the range starting at addr with length len bytes. All pages which contain a part of the speci- fied memory range can after calling munlock be moved to external swap space again by the kernel. Memory locks do not stack, i.e., pages which have been locked several times by calls to mlock or mlockall will be unlocked by a single call to munlock for the corresponding range or by munlockall. Pages which are mapped to several locations or by several processes stay locked into RAM as long as they are locked at least at one location or by at least one process. On POSIX systems on which mlock and munlock are available, _POSIX_MEMLOCK_RANGE is defined in <unistd.h> and the value PAGESIZE from <lim- its.h> indicates the number of bytes per page.
On success, munlock returns zero. On error, -1 is returned, errno is set appropriately, and no changes are made to any locks in the address space of the process.
ENOMEM Some of the specified address range does not correspond to mapped pages in the address space of the process. EINVAL len was not a positive number.
POSIX.1b, SVr4
mlock(2), mlockall(2), munlockall(2) Linux 1.3.43 1995-11-26 MUNLOCK(2)