MEMCNTL(2) System Calls MEMCNTL(2)

NAME

memcntl - memory management control

SYNOPSIS

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

int
memcntl(void *addr, size_t len, int cmd, void *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:

MEMCNTL_SHARED
Page is mapped shared.

MEMCNTL_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 NULL 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. The function returns
immediately once all write operations are scheduled
(unless MS_SYNC is also specified).

MS_SYNC
Perform synchronous writes. 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 NULL 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 NULL,
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.

MT-LEVEL
MT-Safe

SEE ALSO

ppgsz(1), fork(2), mmap(2), mprotect(2), getpagesizes(3C), mlock(3C),
mlockall(3C), msync(3C), plock(3C), sysconf(3C), attributes(7),
privileges(7)

illumos March 13, 2022 illumos