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MLOCK(2)		  FreeBSD System Calls Manual		      MLOCK(2)

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

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #include <sys/types.h>
     #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.
     For both, the addr	parameter should be aligned to a multiple of the page
     size.  If the len parameter is not	a multiple of the page size, it	will
     be	rounded	up to be so.  The entire range must be allocated.

     After an mlock call, the indicated	pages will cause neither a non-resi-
     dent page nor address-translation fault until they	are unlocked.  They
     may still cause protection-violation faults or TLB-miss faults on archi-
     tectures 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 mappings 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.

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:

     [EINVAL]		The address given is not page aligned or the length is
			negative.

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

     [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 were
			locked page accounting is not implemented.

     munlock() will fail if:

     [EINVAL]		The address given is not page aligned or the length is
			negative.

     [ENOMEM]		Some portion of	the indicated address range is not
			allocated.  Some portion 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 distinct 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.

FreeBSD	9.3			 June 2, 1993			   FreeBSD 9.3

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | STANDARDS | HISTORY | BUGS

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