focal (2) mlockall.2freebsd.gz

NAME

     mlockall, munlockall — lock (unlock) the address space of a process

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/mman.h>

     int
     mlockall(int flags);

     int
     munlockall(void);

DESCRIPTION

     The mlockall() system call locks into memory the physical pages associated with the address space of a
     process until the address space is unlocked, the process exits, or execs another program image.

     The following flags affect the behavior of mlockall():

     MCL_CURRENT  Lock all pages currently mapped into the process's address space.

     MCL_FUTURE   Lock all pages mapped into the process's address space in the future, at the time the mapping
                  is established.  Note that this may cause future mappings to fail if those mappings cause
                  resource limits to be exceeded.

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

     If security.bsd.unprivileged_mlock is set to 0 these calls are only available to the super-user.  If
     vm.old_mlock is set to 1 the per-process RLIMIT_MEMLOCK resource limit will not be applied for mlockall()
     calls.

     The munlockall() call unlocks any locked memory regions in the process address space.  Any regions mapped
     after an munlockall() call will not be locked.

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

     mlockall() will fail if:

     [EINVAL]           The flags argument is zero, or includes unimplemented flags.

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

     [EAGAIN]           Some or all of the memory mapped into the process's address space could not be locked
                        when the call was made.

     [EPERM]            The calling process does not have the appropriate privilege to perform the requested
                        operation.

SEE ALSO

     mincore(2), mlock(2), mmap(2), munmap(2), setrlimit(2)

STANDARDS

     The mlockall() and munlockall() functions are believed to conform to IEEE Std 1003.1-2001 (“POSIX.1”).

HISTORY

     The mlockall() and munlockall() functions first appeared in FreeBSD 5.1.

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.