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memcntl(2)
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) accord‐
ing 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 fol‐
lows:
MC_LOCK
Lock in memory all pages in the range with attributes attr. A given
page may be locked multiple times through different mappings; how‐
ever, 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 map‐
ping in the locking process) is locked in memory as long as the
locking process does neither an implicit nor explicit unlock opera‐
tion. If a locked mapping is removed, or a page is deleted through
file removal or truncation, an unlock operation is implicitly per‐
formed. 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.
This command has no effect on segments created with shmget_osm(2).
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.
This command has no effect on segments created with shmget_osm(2).
MC_LOCK_GRANULE
For each granule in the requested region which is not already
locked, it allocates locked-down memory for that granule and
enables access to the region by all processes attached to the
shared memory segment. The newly allocated memory will be entirely
zeroed. The arg, attr, and mask arguments must be NULL, 0, and 0,
respectively, to ensure compatibility with potential future
enhancements.
Since this operation allocates locked memory, it is subjected to
the project.max-locked-memory and zone.max-locked-memory resource
controls, and the overall availability of memory on the system.
The operation may be split into multiple parts; if this occurs, and
a later part fails, any earlier parts which were not previously
locked when the operation started will be unlocked before
MC_LOCK_GRANULE returns.
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_PRI‐
VATE 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 sched‐
uled; 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.
This command has no effect on segments created with shmget_osm(2).
MC_UNLOCK
Unlock all pages in the range with attributes attr. The arg argu‐
ment is not used, but must be 0 to ensure compatibility with poten‐
tial future enhancements.
This command has no effect on segments created with shmget_osm(2).
MC_UNLOCKAS
Remove address space memory locks and locks on all pages in the
address space with attributes attr. The addr, len, and arg argu‐
ments are not used, but must be NULL, 0 and 0, respectively, to
ensure compatibility with potential future enhancements.
This command has no effect on segments created with shmget_osm(2).
MC_CORE_PRUNE_IN
Include the specified address range in the coredump of the process.
The addr and len arguments specify the address range which the user
wants to have included in the coredump.
The arg, attr, and mask arguments must all be set to 0, when using
this command.
MC_CORE_PRUNE_OUT
Exclude the specified address range from the coredump of the
process.
The addr and len arguments specify the address range which the user
wants to have included in the coredump.
The arg, attr, and mask arguments must all be set to 0, when using
this command.
MC_CORE_UNPRUNE
Use the default coredump settings for the specified address range.
The default coredump settings can be found by running coreadm com‐
mand.
The addr and len arguments specify the address range which the user
wants to use as default settings.
The arg, attr, and mask arguments must all be set to 0, when using
this command.
MC_CORE_QUERY
Fill up the character array passed in the arg argument with the
prune policies applied to the address range on a per page basis.
Each entry in the array will have exactly one of the following val‐
ues.
MCQ_DEFAULT Indicates that the corresponding address range
uses default settings.
MCQ_PRUNE_IN Indicates that the corresponding address range
will be included in the coredump of the process.
MCQ_PRUNE_OUT Indicates that the corresponding address range
will be excluded from the coredump of the process.
The caller needs to pass an allocated character array, whose length
will be equal to the number of pages the caller is intend to query.
It is solely the caller's responsibility to ensure enough memory
has been allocated to accommodate all the requested pages.
The attr and mask arguments must be set to 0, when using this com‐
mand.
MC_UNLOCK_GRANULE
For each granule in the requested region which is allocated and
locked, access to the granule is disabled, the granule's allocated
pages are unlocked, and the granule's memory is freed. The arg,
attr, and mask arguments must be NULL, 0, and 0, respectively, to
ensure compatibility with potential future enhancements.
If this operation covers more than a single segment, it may succeed
on earlier segments before returning failure. If so, the earlier
segments will be left unlocked, since their underlying data has
been thrown away.
MC_RESERVE_AS
Reserve the Virtual Address range specified by addr and len. If
successful, the reservation prevents the kernel from using the
Reserved VA range for memory map operations that do not specify
fixed addresses (e.g. library mappings).
The Reserved VA range(s) is 'reserved' for later use by memory map‐
ping operations that specify an address range contained within the
Reserved VA range starting at the addr argument to mmap or the
shmaddr argument to shmat. The reservation can also be left in
place to prevent any other usage of the VA range. For more informa‐
tion, see the mmap(2) and shmat(2) man pages.
The Reserved VA range can be anywhere in the address space that
does not already have a mapping. This includes regions like the
memory hole that may not be valid for actual memory maps.
A fixed address memory mapping operation can freely use the 'valid'
portions of the Reserved VA space automatically. However, if the
mapping range is larger than the Reserved VA range and include
other mappings, the fixed address operation will fail. (mmap(2)
with the MAP_FIXED flag set is the exception as it will indiscrimi‐
nately unmap all mappings in its mapping range.) For guaranteed
success, it is essential that the Reserved VA range is equal to or
larger than the fixed address mapping range.
Please note that the mapfile Empty Segment directive is recommended
for use to create the VA Reservation (For more information, see
Oracle Solaris 11.4 Linkers and Libraries Guide for details). The
MC_RESERVE_AS memcntl command issued from an application occurs
after process startup which could mean that library mappings could
have claimed the desired address range(s) needed for the Reserva‐
tion.
When a program is compiled with the Mapfile Empty Segment direc‐
tive, a VA Reservation is created starting at the specified Empty
Segment Address for the specified Length.
Unlike MC_RESERVE_AS, the VA Reservation Empty Segment directive
should always succeed as the Reservation occurs very early on in
the process startup and the only potential conflict is with the
program text and data and the link-editor would have caught the
conflict during the link-edit. See ld(1) and the Oracle Solaris
11.4 Linkers and Libraries Guide for more details.
MC_UNRESERVE_AS
Unreserve any Reserved Virtual Address range(s) in the address
range specified by addr and len.
If not unreserved via MC_UNRESERVE_AS, the Virtual Address Reserva‐
tions are persistent and lasts until the process exits or executes
a different program.
Mapping ranges that are freed (munmap(2) & shmdt(2)) that had pre‐
viously mapped on top of a Reserved VA range are Re-Reserved.
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 map‐
ping 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.
MC_ENABLE_ADI
Available on platforms that support Application Data Integrity.
Enable ADI on all pages in the range.
The arg, attr, and mask arguments must be NULL, 0, and 0 respec‐
tively, to ensure compatibility with potential future enhancements.
ADI may be enabled on anonymous memory that is mapped PRIVATE or
SHARED and all forms of shared memory attached via shmat(2) except
for DISM.
ADI may only be enabled (or disabled) over the entire range of an
ISM segment.
For a memory segment created with shmget_osm(2), ADI may only be
enabled (or disabled) over a range that starts and ends at a multi‐
ple of the segment's granule size.
When ADI is initially enabled on a region of memory, the ADI ver‐
sions for the region are undefined until they are explicitly set by
the application.
MC_DISABLE_ADI
Available on platforms that support Application Data Integrity.
Disable ADI on all pages in the range.
The arg, attr, and mask arguments must be NULL, 0, and 0 respec‐
tively, to ensure compatibility with potential future enhancements.
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 privi‐
leged processes.
Requests from MC_CORE_PRUNE_IN and MC_CORE_PRUNE_OUT will be honored
only if the core file content specified by coreadm includes the prune
directive. This directive is included in the default set of content
descriptors in coreadm command.
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 hard‐
ware 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:
EACCES MC_LOCK_GRANULE or MC_UNLOCK_GRANULE was specified, and the
requested range covered a non-writable memory segment.
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 iden‐
tified by this operation would exceed a limit or resource
control on locked memory.
The cmd is MC_ENABLE_ADI and the memory identified by this
operation would exceed a limit or resource control on ADI
memory or the total amount of system memory is temporarily
insufficient to allocate ADI metadata.
The cmd is MC_LOCK_GRANULE and the memory identified by this
operation would exceed a limit or resource control.
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.
The mha_pagesize or mha_cmd member is invalid.
MC_HAT_ADVISE is specified and not all pages in the speci‐
fied region have the same access permissions within the
given size boundaries.
MC_HAT_ADVISE is specified for a region of shared memory
either created with shmget_osm(2) or attached with the
SHM_SHARE_MMU or SHM_PAGEABLE attribute.
A prune request was made for an address range, parts of
which are not backed by actual segments in the address
range.
MC_LOCK_GRANULE or MC_UNLOCK_GRANULE was specified, and
either arg was non-NULL, attr was non-zero, mask was non-
zero, or the addr or len arguments were not multiples of the
segment's granule size.
MC_ENABLE_ADI or MC_DISABLE_ADI is specified for a memory
segment which was created with shmget_osm(2), and the range
start or ends at a non-granule multiple.
MC_ENABLE_ADI or MC_DISABLE_ADI is specified for a region of
ISM and the addr and/or len argument do not cover the entire
segment.
MC_ENABLE_ADI or MC_DISABLE_ADI is specified and either arg
was non-NULL, attr was non-zero, or mask was non-zero.
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.
MC_LOCK_GRANULE was specified, and there was not enough
available memory in the system for the request.
ENOSYS MC_LOCK_GRANULE or MC_UNLOCK_GRANULE was specified, and the
requested range covered a memory segment which was not cre‐
ated with shmget_osm(2).
MC_ENABLE_ADI or MC_DISABLE_ADI was specified, and the
requested range covered a memory segment that does not sup‐
port ADI.
ENOTSUP MC_ENABLE_ADI or MC_DISABLE_ADI was specified, and the ADI
feature is not supported by the platform.
MC_ENABLE_ADI or MC_DISABLE_ADI was specified, and the call‐
er is a 32-bit process.
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.
EFAULT The arg argument points to an illegal address.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ MT-LevelMT-Safe
SEE ALSO
ld(1), ppgsz(1), fork(2), mmap(2), mprotect(2), shmget_osm(2), getpage‐
sizes(3C), mlock(3C), mlockall(3C), msync(3C), plock(3C), sysconf(3C),
attributes(7), privileges(7)
Oracle Solaris 11.4 Linkers and Libraries Guide
Oracle Solaris 11.4 15 Jan 2021 memcntl(2)