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NetBSD 6.1.5 - man page for mlock (netbsd section 2)

MLOCK(2)			     BSD System Calls Manual				 MLOCK(2)

NAME
     mlock, munlock -- lock (unlock) physical pages in memory

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/mman.h>

     int
     mlock(void *addr, size_t len);

     int
     munlock(void *addr, size_t len);

DESCRIPTION
     The mlock system call locks into memory the physical pages associated with the virtual
     address range starting at addr for len bytes.  The munlock call unlocks pages previously
     locked by one or more mlock calls.  The entire range of memory must be allocated.

     After an mlock call, the indicated pages will cause neither a non-resident page nor address-
     translation fault until they are unlocked.  They may still cause protection-violation faults
     or TLB-miss faults on architectures with software-managed TLBs.  The physical pages remain
     in memory until all locked mappings for the pages are removed.  Multiple processes may have
     the same physical pages locked via their own virtual address mappings.  A single process may
     likewise have pages multiply-locked via different virtual mappings of the same pages or via
     nested mlock calls on the same address range.  Unlocking is performed explicitly by munlock
     or implicitly by a call to munmap which deallocates the unmapped address range.  Locked map-
     pings are not inherited by the child process after a fork(2).

     Since physical memory is a potentially scarce resource, processes are limited in how much
     they can lock down.  A single process can mlock the minimum of a system-wide ``wired pages''
     limit and the per-process RLIMIT_MEMLOCK resource limit.

     Portable code should ensure that the addr and len parameters are aligned to a multiple of
     the page size, even though the NetBSD implementation will round as necessary.

RETURN VALUES
     A return value of 0 indicates that the call succeeded and all pages in the range have either
     been locked or unlocked.  A return value of -1 indicates an error occurred and the locked
     status of all pages in the range remains unchanged.  In this case, the global location errno
     is set to indicate the error.

ERRORS
     mlock() will fail if:

     [EAGAIN]		Locking the indicated range would exceed either the system or per-process
			limit for locked memory.

     [EINVAL]		The length is negative; or the address or length given is not page
			aligned and the implementation does not round.

     [ENOMEM]		Some portion of the indicated address range is not allocated.  There was
			an error faulting/mapping a page.

     [EPERM]		mlock() was called by non-root on an architecture where locked page
			accounting is not implemented.

     munlock() will fail if:

     [EINVAL]		The length is negative; or the address or length given is not page
			aligned and the implementation does not round.

     [ENOMEM]		Some portion of the indicated address range is not allocated.  Some por-
			tion of the indicated address range is not locked.

SEE ALSO
     fork(2), mincore(2), mmap(2), munmap(2), setrlimit(2), getpagesize(3)

STANDARDS
     The mlock() and munlock() functions conform to IEEE Std 1003.1b-1993 (``POSIX.1'').

HISTORY
     The mlock() and munlock() functions first appeared in 4.4BSD.

BUGS
     The per-process resource limit is a limit on the amount of virtual memory locked, while the
     system-wide limit is for the number of locked physical pages.  Hence a process with two dis-
     tinct locked mappings of the same physical page counts as 2 pages against the per-process
     limit and as only a single page in the system limit.

BSD					February 28, 2011				      BSD


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