System Calls memcntl(2)
NAME
memcntl - memory management control
SYNOPSIS
#include
#include
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 identi-
fied 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 cri-
teria: SHARED Page is mapped shared. PRIVATE Page is mapped private. The following attributes specify page protection selectioncriteria. The selection criteria are constructed by a bit-
wise 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:SunOS 5.11 Last change: 10 Apr 2007 1
System Calls memcntl(2)
PROC_TEXT Process text.
PROC_DATA Process data.
The PROC_TEXT attribute specifies all privately mapped seg-
ments 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 inas 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 oneprocess and mapped in another (or visible through a dif-
ferent mapping in the locking process) is locked in memory as long as the locking process does neither animplicit nor explicit unlock operation. If a locked map-
ping is removed, or a page is deleted through file remo-
val or truncation, an unlock operation is implicitlyperformed. 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:SunOS 5.11 Last change: 10 Apr 2007 2
System Calls memcntl(2)
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. IfMCL_FUTURE is specified, then all mappings subsequently
added to the address space will be locked, provided suf-
ficient 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 modi-
fied MAP_SHARED mapping is the file the page is mapped
to; the backing storage for a modified MAP_PRIVATE map-
ping 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 beobtained by the system from their backing storage loca-
tions. 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. Thearg argument is not used, but must be 0 to ensure compa-
tibility with potential future enhancements.MC_UNLOCKAS
SunOS 5.11 Last change: 10 Apr 2007 3
System Calls memcntl(2)
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, 0and 0, respectively, to ensure compatibility with poten-
tial future enhancements.MC_HAT_ADVISE
Advise system how a region of user-mapped memory will be
accessed. The arg argument is interpreted as a "structmemcntl_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 con-
stant value 0 to allow the system to choose an appropri-
ate 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 toan 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. Seethe NOTES section of the ppgsz(1) manual page for addi-
tional information on process heap alignment.SunOS 5.11 Last change: 10 Apr 2007 4
System Calls memcntl(2)
The attr argument must be 0 for all MC_HAT_ADVISE opera-
tions. The mask argument must be 0; it is reserved for future use. Locks established with the lock operations are not inheritedby 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 opera-
tions 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 applica-
tions 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 sizesmay also introduce extra overhead that could reduce perfor-
mance or available memory. Using large sizes for one appli-
cation 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 notbe 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 insufficientresources 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.SunOS 5.11 Last change: 10 Apr 2007 5
System Calls memcntl(2)
EBUSY When the selection criteria match, some or all of the addresses in the range [addr, addr + len) arelocked and MC_SYNC with the MS_INVALIDATE option
was specified.EINVAL The addr argument specifies invalid selection cri-
teria or is not a multiple of the page size as returned by sysconf(3C); the addr and/or lenargument 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 speci-
fied 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 pro-
cess and MC_LOCK, MC_LOCKAS, MC_UNLOCK, or
MC_UNLOCKAS was specified.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| 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(5), privileges(5)SunOS 5.11 Last change: 10 Apr 2007 6