memcntl - memory management control
#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);
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:
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.
The following criteria may also be specified:
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:
The arg argument is not used, but must be 0 to ensure compatibility with potential future enhancements.
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.
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.
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.
The memcntl() function subsumes the operations of plock(3C) and mctl(3UCB).
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.
Upon successful completion, memcntl() returns 0; otherwise, it returns -1 and sets errno to indicate an error.
The memcntl() function will fail if:
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.
See attributes(5) for descriptions of the following attributes:
ppgsz(1), fork(2), mmap(2), mprotect(2), getpagesizes(3C), mctl(3UCB), mlock(3C), mlockall(3C), msync(3C), plock(3C), sysconf(3C), attributes(5), privileges(5)
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Created 1996-2021 by Maxim Chirkov
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