mlock man page on NetBSD

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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-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.

     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 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.

BSD			       February 28, 2011			   BSD
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