illumos: manual page: memcntl.2

MEMCNTL(2) System Calls MEMCNTL(2)

NAME

memcntl - memory management control

SYNOPSIS

#include <sys/types.h>
#include <sys/mman.h>

int memcntl(caddr_t addr, size_t len, int cmd, caddr_t arg,
int attr, int mask);

DESCRIPTION

The memcntl() function allows the calling process to apply a variety of
control operations over the address space identified by the mappings
established for the address range [addr, addr + len).

The addr argument must be a multiple of the pagesize as returned by
sysconf(3C). The scope of the control operations can be further defined
with additional selection criteria (in the form of attributes) according
to the bit pattern contained in attr.

The following attributes specify page mapping selection criteria:

SHARED
Page is mapped shared.

PRIVATE
Page is mapped private.

The following attributes specify page protection selection criteria. The
selection criteria are constructed by a bitwise OR operation on the
attribute bits and must match exactly.

PROT_READ
Page can be read.

PROT_WRITE
Page can be written.

PROT_EXEC
Page can be executed.

The following criteria may also be specified:

PROC_TEXT
Process text.

PROC_DATA
Process data.

The PROC_TEXT attribute specifies all privately mapped segments with read
and execute permission, and the PROC_DATA attribute specifies all
privately mapped segments with write permission.

Selection criteria can be used to describe various abstract memory
objects within the address space on which to operate. If an operation
shall not be constrained by the selection criteria, attr must have the
value 0.

The operation to be performed is identified by the argument cmd. The
symbolic names for the operations are defined in <sys/mman.h> as follows:

MC_LOCK

Lock in memory all pages in the range with attributes attr. A given
page may be locked multiple times through different mappings;
however, within a given mapping, page locks do not nest. Multiple
lock operations on the same address in the same process will all be
removed with a single unlock operation. A page locked in one process
and mapped in another (or visible through a different mapping in the
locking process) is locked in memory as long as the locking process
does neither an implicit nor explicit unlock operation. If a locked
mapping is removed, or a page is deleted through file removal or
truncation, an unlock operation is implicitly performed. If a
writable MAP_PRIVATE page in the address range is changed, the lock
will be transferred to the private page.

The arg argument is not used, but must be 0 to ensure compatibility
with potential future enhancements.

MC_LOCKAS

Lock in memory all pages mapped by the address space with attributes
attr. The addr and len arguments are not used, but must be NULL and 0
respectively, to ensure compatibility with potential future
enhancements. The arg argument is a bit pattern built from the
flags:

MCL_CURRENT
Lock current mappings.

MCL_FUTURE
Lock future mappings.

The value of arg determines whether the pages to be locked are those
currently mapped by the address space, those that will be mapped in
the future, or both. If MCL_FUTURE is specified, then all mappings
subsequently added to the address space will be locked, provided
sufficient memory is available.

MC_SYNC

Write to their backing storage locations all modified pages in the
range with attributes attr. Optionally, invalidate cache copies. The
backing storage for a modified MAP_SHARED mapping is the file the
page is mapped to; the backing storage for a modified MAP_PRIVATE
mapping is its swap area. The arg argument is a bit pattern built
from the flags used to control the behavior of the operation:

MS_ASYNC
Perform asynchronous writes.

MS_SYNC
Perform synchronous writes.

MS_INVALIDATE
Invalidate mappings.

MS_ASYNC Return immediately once all write operations are scheduled;
with MS_SYNC the function will not return until all write operations
are completed.

MS_INVALIDATE Invalidate all cached copies of data in memory, so that
further references to the pages will be obtained by the system from
their backing storage locations. This operation should be used by
applications that require a memory object to be in a known state.

MC_UNLOCK

Unlock all pages in the range with attributes attr. The arg argument
is not used, but must be 0 to ensure compatibility with potential
future enhancements.

MC_UNLOCKAS

Remove address space memory locks and locks on all pages in the
address space with attributes attr. The addr, len, and arg arguments
are not used, but must be NULL, 0 and 0, respectively, to ensure
compatibility with potential future enhancements.

MC_HAT_ADVISE

Advise system how a region of user-mapped memory will be accessed.
The arg argument is interpreted as a "struct memcntl_mha *". The
following members are defined in a struct memcntl_mha:

uint_t mha_cmd;
uint_t mha_flags;
size_t mha_pagesize;

The accepted values for mha_cmd are:

MHA_MAPSIZE_VA
MHA_MAPSIZE_STACK
MHA_MAPSIZE_BSSBRK

The mha_flags member is reserved for future use and must always be
set to 0. The mha_pagesize member must be a valid size as obtained
from getpagesizes(3C) or the constant value 0 to allow the system to
choose an appropriate hardware address translation mapping size.

MHA_MAPSIZE_VA sets the preferred hardware address translation
mapping size of the region of memory from addr to addr + len. Both
addr and len must be aligned to an mha_pagesize boundary. The entire
virtual address region from addr to addr + len must not have any
holes. Permissions within each mha_pagesize-aligned portion of the
region must be consistent. When a size of 0 is specified, the system
selects an appropriate size based on the size and alignment of the
memory region, type of processor, and other considerations.

MHA_MAPSIZE_STACK sets the preferred hardware address translation
mapping size of the process main thread stack segment. The addr and
len arguments must be NULL and 0, respectively.

MHA_MAPSIZE_BSSBRK sets the preferred hardware address translation
mapping size of the process heap. The addr and len arguments must be
NULL and 0, respectively. See the NOTES section of the ppgsz(1)
manual page for additional information on process heap alignment.

The attr argument must be 0 for all MC_HAT_ADVISE operations.

The mask argument must be 0; it is reserved for future use.

Locks established with the lock operations are not inherited by a child
process after fork(2). The memcntl() function fails if it attempts to
lock more memory than a system-specific limit.

Due to the potential impact on system resources, the operations
MC_LOCKAS, MC_LOCK, MC_UNLOCKAS, and MC_UNLOCK are restricted to
privileged processes.

USAGE

The memcntl() function subsumes the operations of plock(3C).

MC_HAT_ADVISE is intended to improve performance of applications that use
large amounts of memory on processors that support multiple hardware
address translation mapping sizes; however, it should be used with care.
Not all processors support all sizes with equal efficiency. Use of larger
sizes may also introduce extra overhead that could reduce performance or
available memory. Using large sizes for one application may reduce
available resources for other applications and result in slower system
wide performance.

RETURN VALUES

Upon successful completion, memcntl() returns 0; otherwise, it returns -1
and sets errno to indicate an error.

ERRORS

The memcntl() function will fail if:

EAGAIN
When the selection criteria match, some or all of the memory
identified by the operation could not be locked when MC_LOCK or
MC_LOCKAS was specified, some or all mappings in the address
range [addr, addr + len) are locked for I/O when MC_HAT_ADVISE
was specified, or the system has insufficient resources when
MC_HAT_ADVISE was specified.

The cmd is MC_LOCK or MC_LOCKAS and locking the memory
identified by this operation would exceed a limit or resource
control on locked memory.

EBUSY
When the selection criteria match, some or all of the addresses
in the range [addr, addr + len) are locked and MC_SYNC with the
MS_INVALIDATE option was specified.

EINVAL
The addr argument specifies invalid selection criteria or is
not a multiple of the page size as returned by sysconf(3C); the
addr and/or len argument does not have the value 0 when
MC_LOCKAS or MC_UNLOCKAS is specified; the arg argument is not
valid for the function specified; mha_pagesize or mha_cmd is
invalid; or MC_HAT_ADVISE is specified and not all pages in the
specified region have the same access permissions within the
given size boundaries.

ENOMEM
When the selection criteria match, some or all of the addresses
in the range [addr, addr + len) are invalid for the address
space of a process or specify one or more pages which are not
mapped.

EPERM
The {PRIV_PROC_LOCK_MEMORY} privilege is not asserted in the
effective set of the calling process and MC_LOCK, MC_LOCKAS,
MC_UNLOCK, or MC_UNLOCKAS was specified.

ATTRIBUTES