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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(const void *addr, size_t len);

     int
     munlock(const 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.

     These calls are only available to the super-user.

RETURN VALUES
     Upon successful completion, the value 0 is	returned; otherwise the
     value -1 is returned and the global variable errno	is set to indicate the
     error.

     If	the call succeeds, all pages in	the range become locked	(unlocked);
     otherwise the locked status of all	pages in the range remains unchanged.

ERRORS
     Mlock() will fail if:

     [EPERM]		The caller is not the super-user.

     [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.
     Munlock() will fail if:

     [EPERM]		The caller is not the super-user.

     [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), minherit(2), mmap(2),	munmap(2), setrlimit(2),
     getpagesize(3)

BUGS
     Unlike The	Sun implementation, multiple mlock() calls on the same address
     range require the corresponding number of munlock() calls to actually
     unlock the	pages, i.e. mlock() nests.  This should	be considered a	conse-
     quence of the implementation and not a feature.

     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.

     The per-process resource limit is not currently supported.

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

FreeBSD	9.2			 June 2, 1993			   FreeBSD 9.2

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

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