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sys_attrs

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NAME

sys_attrs, sys_attrs_cm, sys_attrs_generic, sys_attrs_ipc, sys_attrs_proc, sys_attrs_vfs, sys_attrs_vm - introduction to kernel subsystem attributes used for configuration and tuning and descriptions of attributes for required subsystems  

DESCRIPTION

The operating system kernel is built from many mandatory and optional subsystems. If you are logged into the root account, the following command lists the subsystems included in the kernel for your system: # /sbin/sysconfig -s

The majority of the kernel subsystems have sets of attributes whose values control different aspects of subsystem configuration. You can examine the names, the current settings, and (if applicable) the minimum, and maximum settings of attributes for a particular subsystem by entering the command /sbin/sysconfig -Q subsystem-name or by using the dxkerneltuner application in the Common Desktop Environment (CDE).

Caution

A relatively small number of the attributes listed in displays from these interfaces should actually be changed through these same interfaces and then only as part of the system configuration and tuning tasks done by an experienced system or network administrator. The settings of most subsystem attributes should be done indirectly through system and network setup applications or scripts. This fact is very important to remember because attribute settings can have complex interrelationships with one another, requiring (in some cases) careful manipulation of an entire set of attributes rather than only one. Furthermore, default settings of some subsystem attributes should never be touched, except by Compaq support personnel or by an administrator acting on instructions from support personnel or patch kit documentation.

Some attributes have corresponding parameters in the system configuration file. If so, the corresponding parameter name in the system configuration file is specified in parentheses following the attribute name. In these cases, never edit the system configuration file to directly change the value of the system parameter; use the dxkerneltuner application or the /sbin/sysconfig -r command to change the value of the attribute. For some subsystems, these values are best applied through a stanza-formatted file that is specified as a parameter to the sysconfigdb command. See dxkerneltuner(8X), sysconfig(8), and sysconfigdb(8) for more information about your options for configuring kernel subsystems.

This reference page lists and describes attributes for subsystems that must be included when the kernel is built. These subsystems include the following ones: Configuration Manager (cm) Generic Kernel (generic) Interprocess Communication (ipc) Process (proc) Virtual File System (vfs) Virtual Memory (vm)

A kernel also includes a processor-specific subsystem whose name is an internal code for a particular processor. Processor-specific subsystems typically have no attributes, are not modified directly by users, and are not documented.

Other kernel subsystems are technically optional, although a kernel almost always includes quite a few optional subsystems in order for a system to be useful. For information on the attributes for kernel subsystems that are technically optional, refer to the system attributes reference pages for particular subsystems. The names of these reference pages adhere to the format sys_attrs_subsystem-name. For example, the reference page that lists and describes attributes for the pci subsystem is named sys_attrs_pci(5).

For guidelines on changing kernel subsystem attributes to improve system performance, see the System Configuration and Tuning manual. Any discussion about changing attributes for reasons other than tuning is located in the administration manual that discusses that subsystem.

Some subsystem attributes can be changed at run time. If so, the attribute descriptions in the following subsections mention that fact. To make it easy for you to locate these attributes when scanning lists, an asterisk (*) also precedes the names of these attributes.
 

cm Subsystem Attributes

The maximum number of registered callbacks that are allowed by the kernel at any point in time. If exceeded, register_callback() (a function used only by kernel components, such as device drivers) receives an error message.
Default value: 341 (callbacks)
Do not modify the default setting for this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit instructions.
 

generic Subsystem Attributes

The kernel buffer size in bytes.
Default value: If the binlog-buffer-size is not explicitly specified, the value for kernel buffer size is assigned at boot time and is based on the amount of physical memory installed on the system. The value assigned automatically ranges from 32 kilobytes to 1 megabyte.
Minimum value: 8192 (bytes, or 8 KB)
Maximum value: 1048576 (bytes, or 1 MB)
The arguments passed from osf_boot to the kernel.
The name of the kernel that was loaded by osf_boot.
The number of clock interrupts per second. This value is platform dependent and can only be queried.
A value for the bit mask that determines which CPUs can be started in a multi-CPU system. The lowest order bit (bit 0) in this mask corresponds to CPU0. The next highest order bit corresponds to CPU1, and so on, up to bit 63. The bits in these positions can be set to 0 (disabled) or 1 (enabled) for the corresponding CPU slots. The decimal or hexidecimal value specified for cpu_enable_mask corresponds to the binary value that has 0 and 1 in the correct ordinal positions for the CPUs you want to enable or disable.
Default value: 18446744073709551615 (same as -1)
Minimum value: 0
Maximum value: 18446744073709551615 (same as -1)
Specifying -1 for this attribute means that all CPUs present in the system are allowed to be started by the master CPU. Specifying 0 for this attribute enables uniprocessor operation in a multi-CPU system. Other values enable and disable specific CPUs, depending on what the system supports.
The following table illustrates the relationships between bit settings and cpu_enable_mask values for enabling a single CPU. It is generally easier to determine and enter hexidecimal values, so only a few significant decimal equivalents are shown:

                              Dec.   Hex                 Single Bit 63... 8 7 6 5 4 3 2 1 0 Value Value CPU Enabled __________________________________________________________________________
    0 ... 0 0 0 0 0 0 0 0 0   0      0                   Special meaning *
    0 ... 0 0 0 0 0 0 0 0 1   1      0x1                 CPU0
    0 ... 0 0 0 0 0 0 0 1 0          0x2                 CPU1
    0 ... 0 0 0 0 0 0 1 0 0          0x4                 CPU2
    0 ... 0 0 0 0 0 1 0 0 0          0x8                 CPU3
    0 ... 0 0 0 0 1 0 0 0 0          0x10                CPU4
    0 ... 0 0 0 1 0 0 0 0 0          0x20                CPU5
    0 ... 0 0 1 0 0 0 0 0 0          0x40                CPU6
    0 ... 0 1 0 0 0 0 0 0 0          0x80                CPU7
    0 ... 1 0 0 0 0 0 0 0 0          0x100               CPU8
       .
       .
       .
    1 ... 0 0 0 0 0 0 0 0 0          0x8000000000000000  CPU63
* The minimum value (0) indicates that only the master (boot) CPU be enabled. This value is useful if you want to test applications in a uniprocessor environment and your test system normally runs in multiprocessor mode.
Note
Most systems require that the master CPU be CPU0. For these systems, 0 and 1 are equivalent values and are the only values you should specify for uniprocessor operation. Keep in mind that the kernel determines which CPU is the master CPU on these systems and will overwrite values specified for cpu_enable_mask that are incompatible with having CPU0 as the master CPU.
The following table illustrates the relationships between bit settings and cpu_enable_mask values for enabling sample combinations of CPUs:

                             Dec.   Hex                 Multiple Bit 63... 8 7 6 5 4 3 2 1 0 Value Value CPUs Enabled _____________________________________________________________________________
    0 ... 0 0 0 0 0 0 0 1 1         0x3                 CPU0, CPU1
    0 ... 0 0 0 0 0 0 1 0 1         0x5                 CPU0, CPU2
    0 ... 0 0 0 0 0 0 1 1 0         0x6                 CPU1, CPU2
    0 ... 0 0 0 0 0 0 1 1 1         0x7                 CPU0, CPU1, CPU2
       .
    0 ... 0 0 0 0 0 1 1 1 1         0xf                 CPU0 to CPU3
       .
    0 ... 0 0 0 0 1 1 1 1 1         0x1f                CPU0 to CPU4
       .
    0 ... 0 0 0 1 1 1 1 1 1         0x3f                CPU0 to CPU5
       .
    0 ... 0 0 1 1 1 1 1 1 1         0x7f                CPU0 to CPU6
       .
    0 ... 0 1 1 1 1 1 1 1 1         0xff                CPU0 to CPU7
       .
    0 ... 1 1 1 1 1 1 1 1 1         0x1ff               CPU0 to CPU8
       .
       .
       .
    1 ... 1 1 1 1 1 1 1 1 1  -1     0xffffffffffffffff  All available CPUs *
* The maximum value specifies 1 in all bit positions, thereby enabling all available CPUs. This value corresponds to 18446744073709551615 or -1 in decimal notation or 0xffffffffffffffff in hexidecimal notation.
You can enable and disable specific combinations of CPUs by entering values that set and clear appropriate bit positions in the bit mask. If you suspect that one of the CPUs on a multiprocessor system may be the cause of a system problem, you can try running the system with different combinations of available CPUs disabled to help confirm your suspicion. Remember that if your system is one of those that require CPU0 to be the master CPU, the kernel does not apply values that map to 0 in bit position 0. In this case, you have to switch another CPU into slot 0 before you can do a test run that disables the CPU originally in slot 0.
Certain lockmode attribute values override incompatible cpu_enable_mask settings. If the value of the lockmode attribute is 0 or 1, all bits in the cpu_enable_mask bit mask that do not correspond to the master CPU are set to 0.
A threshold size that determines whether single-partition or multiple-partition dumps are created. If a dump will fit on the primary swap partition and leave space that is equal to this threshold value, the dump is created as a single-volume dump on the primary swap partition, even if secondary swap partitions are available. (See the Kernel Debugging manual for details.)
Default value: 4096
An interactive boot flag that is used for diagnostic purposes only.
If enabled (1), each time the kernel memory allocator allocates or deallocates memory in the kernel memory pool, the system checks whether the operation is performed correctly. If the kernel memory pool is in a corrupt state, the system crashes and provides useful debugging information.
A setting that enables (1) or disables (0) a set of attribute values that improve performance for 32-MB systems.
Default value: 1 if memory size is less than or equal to 32 MB and 0 if memory size is greater than 32 MB
Do not modify the default setting for this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation.
A value that enables (1) or disables (0) lock debugging. If enabled (1), the default value for the lockmode attribute is set to 4.
If you explicitly specify a value for the lockmode attribute, that value also causes lockdebug to be set or reset (overridden). For example, if you set lockmodeto be 0, 1, 2, or 3, the value of lockdebug will be 0. If you set lockmode to be 4, the value of lockdebug will be 1.
Default value: 0 (disabled)
Used for internal debugging.
Default value: 0
Do not modify the default setting for this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation.
The mode in which the simple lock primitive package is used within the kernel. Mode settings support different combinations of real-time (RT) kernel preemption, symmetric multiprocessing (SMP), and lock debugging with lock statistics: Neither RT nor SMP is required. In this case, the calls to the simple lock primitives are patched out completely. Only RT is required. In this case, the simple lock operations maintain a ``preemption blocking'' count. Only SMP is required. In this case, the lock operations provide synchronization among multiple CPUs. Both RT and SMP are required. In this case, lock operations are performed as described for both mode 1 and 2. Both RT and SMP are required. In this case, lock operations are as described for mode 3, with the addition of kernel lock debugging and statistics.
Default value: Assigned at boot time, depending on the values for the rt_preempt_opt, cpu_enable_mask, and lockdebug attributes, and on whether multiple CPUs are able to be booted.
If you specify a value for lockmode (0-4), your setting both overrides the default setting and disables any of the three related capabilities that cannot be supported by the chosen set of simple lock primitives. For example, setting lockmode to 0, 1, 2, or 3 disables kernel lock debugging and statistics, whether or not the lockdebug attribute was originally set to 1 (to enable kernel lock debugging and statistics).
The number of seconds that a CPU will wait (spin) on a simple lock. If a CPU cannot acquire a simple lock in the specified amount of time, a fatal error occurs, and the system panics and issues a "simple_lock:time limit exceeded" message.
Default value: 15 (seconds)
Do not modify the default setting for this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit instructions. A 0 value might cause boot failures on a multiprocessor system. Values larger than the default might hang the system instead of causing it to panic and reboot.
The depth to which complex locks can be nested for a thread at one time. The value of max-lock-per-thread is used for debugging (when lockmode=4).
Default value: 16
Do not modify the default setting for this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation.
The size of the message buffer that is used to store boot log messages.
Default value: 4096
Do not modify the default setting for this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation.
Default value: 1 (on)
A value that controls how I/O requests are gathered when readv or writev operations are directed at a character device (not a block device). For example, when set to 65536, eight 8-KB buffers coalesce into one 64-KB buffer. This improves the efficiency of database operations.
Default value: 65536
Do not modify the default setting for this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation.
A value that enables (1) or disables (0) real-time kernel preemption.
Default value: 0 (disabled)
If real-time kernel preemption is enabled (1), the default value for lockmode will be 1 on a single-CPU system or 3 on a multi-CPU system. However, if you explicitly specify certain lockmode values, you implicitly override the rt-preempt-opt value. For example, if you set lockmode to 0 or 2, you implicitly set rt-preempt-opt to 0, disabling real-time kernel preemption.
The CFG run-time points that are configurable from user mode. Setting this attribute to a particular value triggers kernel callbacks that have been registered for the point corresponding to that value.
Default value: 0 (callbacks disabled)
Do not modify the default setting for this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation.
 

ipc Subsystem Attributes

The maximum number of kernel IPC ports that can be used on the system at one time.
Default value: (task-max * 3 + thread-max) + (thread-max * 2) + 2000
(Values of variables used to establish default value: task-max = nproc +1; thread-max = nproc *2; nproc = 20 + 8 * maxusers)
Do not modify the default setting for this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation.
Maximum size, in bytes, of a single System V message.
Default value: 8192 (bytes, which equal 1 page)
Minimum value: 0
Maximum value: INT_MAX
Values for this attribute are restricted by the amount of main memory on the system. The minimum value (0) disables the messaging system.
Maximum number of bytes that can be queued to a single System V message queue.
Default value: 16384 (bytes, which equal 2 pages)
Minimum value: 0
Maximum value: INT_MAX
Values for this attribute are restricted by the amount of main memory on the system. The minimum value (0) disables the messaging system.
Maximum number of System V message queues that can be used on the system at one time.
Default value: 50 (queues) The system rounds the number to the value associated with the next higher power of two; for example, 64.
Minimum value: 0
Maximum value: INT_MAX
Values for this attribute are restricted by the amount of main memory on the system. The minimum value (0) disables the messaging system.
Maximum number of messages that can be queued to a single System V message queue at one time.
Default value: 40 (messages)
Minimum value: 0
Maximum value: INT_MAX
Values for this attribute are restricted by the amount of main memory on the system. The minimum value (0) disables the messaging system.
Obsolete. Not used.
Number of port hash buckets that the kernel uses to manage the kernel ports.
Default value: 50 * max-kernel-ports
Do not modify the default setting for this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation.
Maximum number of ports that can be reserved by the kernel.
Default value: max-kernel-ports
Do not modify the default setting for this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation.
A value that controls the maximum adjustment that can be made to any System V semaphore when a process exits.
Default value: 16384
Minimum value: 0
Maximum value: 65536
Maximum number of System V semaphores that can be used on the system at one time.
Default value: 10 (semaphores) (The system rounds the number to the value associated with the next higher power of two; for example, 16.)
Minimum value: 0
Maximum value: INT_MAX
Maximum number of System V semaphores that can be used by a single process at one time.
Default value: 25 (semaphores)
Minimum value: 0
Maximum value: INT_MAX
Maximum number of operations that can be outstanding on a single System V semaphore at one time.
Default value: 10 (operations)
Minimum value: 0
Maximum value: INT_MAX
Maximum number of undo operations that can be outstanding on a single System V semaphore at one time.
Default value: 10 (operations)
Minimum value: 0
Maximum value: INT_MAX
Maximum integer value that any System V semaphore can contain.
Default value: 32767
Minimum value: 0
Maximum value: INT_MAX, but do not enter values higher than 65535
Maximum number of port sets that can be used by the kernel at one time.
Default value: task-max + thread-max + 200
(Values of variables used to establish default value: task-max = nproc +1; thread-max = nproc *2; nproc = 20 + 8 * maxusers)
Do not modify the default setting for this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation.
Maximum size, in bytes, of a single System V shared memory region.
Default value: 4194304 (bytes) (This value equals 512 pages)
Minimum size, in bytes, of a single System V shared memory region.
Default value: 1 (All requests are rounded to the next page size.)
Maximum number of shared memory regions that can be used on the system at one time.
Default value: 100 (regions) (The system rounds the number to the value associated with the next higher power of two; for example, 128.)
Maximum number of System V shared memory regions that can be attached to a single process at one time.
Default value: 32 (regions)
If enabled (1), writes segmented shared memory contents when an application issues a core dump. If disabled (0), segmented shared memory is not written to the core dump.
Default value: 1 (enabled)
Because segmented shared memory can be large, the amount of time needed to dump the region to a core file and the amount of file system space required by the operation can be extensive, especially in large database environments. Therefore, although shared memory can be useful for debugging, you may not want to include it in core files because of time and resource limitations.
This attribute can be modified at run time.
The minimum size, in bytes, of a System V shared region for the use of shared page tables. Setting this value to 0 disables the use of shared page tables for shared memory. The size must be at least equal to the value of SSM_SIZE, which is defined in the machine/pmap.h file (the default is 8 MB).
This attribute can be modified at run time.
Default value: SSM_SIZE
Minimum value: SSM_SIZE
 

proc Subsystem Attributes

A value that enables (1) or disables (0) the ability of applications that use more than 600 seconds of CPU time to automatically increase their nice values (that is, lower their scheduling priorities).
Default value: 0 (disabled)
The nice value that is assigned to a process after it has used an amount of CPU time that exceeds the value of the autonice-time attribute.
Default value: 4
Minimum value: 0
Maximum value: 20
The amount of CPU time, in seconds, that a process can use before it is assigned the nice value that is specified by the autonice-penalty attribute.
Default value: 600 (seconds)
Minimum value: 0
Maximum value: 86400
The maximum number of unique core files that a program can create on a host system.
Default value: 16 (files)
Minimum value: 1
Maximum value: 99,999
A value that enables (1) or disables (0) creation of multiple versions of core files. If this attribute is set to 0, an existing core file will be overwritten when a new one is created.
Default value: 0 (disabled)
A value that enables (1) or disables (0) booting the priority of processes that have recently awakened from a block I/O operation. Setting this attribute to 1 reduces I/O latency and may make the system more responsive.
Default value: 1 (enabled)
Maximum amount, in bytes, of user process address space.
Default value: 107374182 (bytes) (1 GB)
Minimum value: 0
Maximum value: 4398046511104
Maximum size, in bytes, of a data segment for each process.
Default value: 107374182 (bytes) (1 GB)
Maximum size, in bytes, of a user process stack.
Default value: 33554432 (bytes)
Minimum value: 0
Maximum value: 4398046511104
Maximum number of processes (tasks) that a user can create. (The superuser is not affected.)
Default value: 64 (processes)
Minimum value: 0
Maximum value: 32768
If you specify 0 for this attribute, the system does not check how many processes a user creates.
Maximum limit of threads a user can create. (The superuser is not affected.)
Default value: 256 (threads)
Minimum value: 0
Maximum value: LONG_MAX
If you specify 0 for this attribute, the system does not check how many threads a user creates.
Number of simultaneous users that a system can support without straining system resources. System algorithms use the maxusers keyword to size various system data structures and to determine the amount of space allocated to system tables, such as the system process table.
Default value: System dependent
Minimum value: 8
Maximum value: 4096
Increasing the value of the maxusers attribute allocates more system resources to the kernel. However, it also increases the amount of physical memory consumed by the kernel. Changing the value of the maxusers attribute affects the values of other attributes, including the taskmax, threadmax, and min-free-vnodes attributes.
Obsolete. Not used.
Minimum amount of memory that can be used for timeout tables. The value of this attribute is automatically adjusted.
Do not modify the default setting for this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation. The number of callout tables. This number determines the size of the hash table for timeout queues.
Default value: The number of process slots divided by 32
Do not modify the default setting for this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation. The size of the hash table for the wait queue.
Default value: The number of process slots divided by 32
Minimum value: 64
Maximum value: 16384
Hard limit for the number of file descriptors for each process.
Default value: 4096 (file descriptors)
Minimum value: 0
Maximum value: 65536
If the number of file descriptors reaches the value of the open-max-hard attribute or higher, the process is stopped. Use the getdtablesize() system call to obtain the total number of file descriptors in a process' descriptor table.
The soft limit for the number of file descriptors for a process.
Default value: 4096 (file descriptors)
Minimum value: 0
Maximum value: 65536
When the open-max-soft limit is reached, a warning message is issued. Use the getdtablesize() system call to obtain the total number of file descriptors in a process' descriptor table. A process can increase its soft limit up to its hard limit (open-max-hard) by using the setrlimit() system call.
The maximum amount, in bytes, of user process address space.
Default value: 107374182 (bytes) (1 GB)
Minimum value: 0
Maximum value: 4398046511104
Current maximum size of a data segment for each process.
Default value: 134217728
Minimum value: 0
Maximum value: 4398046511104
The maximum size of a user process stack.
Default value: 2097152
Minimum value: 0
Maximum value: 4398046511104
The number of context switches per second that can occur between processes with the same priority. The lower the number, the less the system timeslices; the higher the number, the more the system timeslices.
Default value:
Minimum value: 0
Maximum value: 1024
Time, in clock ticks, that a thread must remain idle on a multiprocessor system before it is eligible to migrate to another processor.
Default value: 0 (clock ticks)
Minimum value: 0
Maximum value: INT_MAX
This attribute is used to tune the soft affinity algorithm on multiprocessor systems. Soft affinity enables a process to stay where it last ran, and thereby optimize its use of any data or instructions that it had brought into cache memory. The sched-min-idle attribute is used only on multiprocessor systems; it has no effect on single-CPU systems.
Maximum number of tasks that can run simultaneously on the system.
Default value: 20 + 8 * maxusers
Minimum value: 85
Maximum value: 32769
Maximum number of kernel threads that can run simultaneously on the system.
Default value: 2 * task-max
Minimum value: 160
Maximum value: 262144
 

vfs Subsystem Attributes

Percentage of memory that the kernel wires for the metadata buffer cache.
Default value: 3 (percent) for 32-MB or larger systems; 2 (percent) for 24-MB systems
Minimum value: 0
Maximum value: 50
Increasing the value of the bufcache attribute can improve I/O performance by providing more memory for caching UFS file system data. Decreasing the value of the bufcache attribute can free memory resources. For systems that cache only AdvFS file system data, you may want to decrease the value to 1.
Size, in slots, of the hash chain table for the metadata buffer cache. The hash chain table is used to store the heads of the hashed buffer queues.
Default value: 512 (slots)
Minimum value: 0
Maximum value: 2147483647
A large hash chain table distributes the buffers and may make chain lengths short. Increasing the size of the hash chain table can reduce linear searches and improve lookup speed.
A value that enables (1) or disables (0) the pipe code that attempts to batch writes to a pipe and deliver the data in a single call to a reader.
Default value: 1 (enabled)
Maximum number of file structures on the free list. When the number of free file structures that are chained for reuse on the free list reaches the value of the max_free_files attribute, file structure deallocation begins.
Default value: 0 (file structures)
Minimum value: 0
Maximum value: 2147483647
You can modify this attribute at run time.
Maximum number of UFS or MFS file system mounts. You can increase the value of the max-ufs-mounts attribute if you want to mount more than the default number of UFS or MFS file systems. This attribute does not affect performance.
Default value: 1000
Minimum value: 0
Maximum value: (No limit)
You can modify this attribute at run time.
Maximum number of vnodes (open files) on a system.
Default value: 1000 (for 24-MB systems); the maximum value (for 32-MB or larger systems)
Minimum value: Specified by the nvnode attribute
Maximum value: The number of vnodes that 5 percent of the available memory can contain
Increasing the value of the max-vnodes attribute allows more vnodes on a system, which may improve performance if your applications or users create a large number of open files. However, supporting more vnodes uses additional memory.
You can modify this attribute at run time.
Minimum number of free vnodes on the free list. If the number of vnodes on the free list is less than the value of the min-free-vnodes attribute, vnodes are deallocated.
Default value: nvnode attribute (for 32-MB or larger systems); 150 (for 24-MB systems)
Minimum value: 0
Maximum value: 2147483647
Increasing the value causes the system to cache more free vnodes and may improve performance for vnode cache lookup operations. However, a large value increases the demand for memory.
You can modify this attribute at run time.
Size, in slots, of the hash chain table for the namei cache.
Default value: 256 slots
Minimum value: 0
Maximum value: name-cache-size/2
Large hash chain tables distribute the namei cache elements and may make chain lengths short, which can reduce linear searches and improve lookup speeds. In general, chains should contain only 2 or 3 elements.
Number of elements in the namei cache.
Default value: 2*nvnode*11/10 (for 32-MB or larger systems); 150 (for 24-MB systems)
Minimum value: 0
Maximum value: 2*max-vnodes*11/10
Increasing the value of the name-cache-size attribute may improve lookup speeds, but it requires more memory. Decreasing the value can free memory.
Amount of time, in seconds, that a namei cache entry can remain in the cache before it is discarded.
Default value: 1200 (seconds) for 32-MB or larger systems; 30 (seconds) for 24-MB systems
Minimum value: 0
Maximum value: 2147483647
A large namei-cache-valid-time attribute value will retain more vnodes references in the namei cache and improve the namei cache lookup speed; however, it will require more memory resources. A small value may cause premature deallocation of vnodes and decrease the namei cache lookup speed.
A value that allows you to configure your system so that new executables cannot be created. This is a security feature and does not affect performance.
Default value: 0
Minimum value: 0
Maximum value: 4294967295
Obsolete. Retained only for compatibility purposes. Determines the maximum and the minimum number of vnodes on a system. If you modify the value of the nvnode attribute and then reboot the system, the lockfile zone size and the specinfo_zone size allocation are also modified.
Default value: nproc+(2*maxusers)+128
Minimum value: 0
Maximum value: 2147483647
Size, in number of zone elements, of the pathname zone for pathname lookup buffers. Increasing the value of path-num-max increases the number of elements in the zone that is allocated for pathnames.
Default value: 64 (zone elements)
Minimum value: 0
Maximum value: 2147483647
Number of data bytes in each pipe data buffer.
Default value: 8192 (bytes)
Maximum number of bytes reserved for all pipes.
Default value: 819200 (bytes)
Minimum value: 819200
Maximum value: 2147483647
Maximum number of bytes buffered per pipe.
Default value: 65536 (bytes, or 64 KB)
Minimum value: 4096
Maximum value: 262144
Maximum size of a single write to a pipe.
Default value: -1
Size of the special vnodes alias table for vnodes of special device files, such as character-I/O or block-I/O device files.
Default value: 64
Minimum value: 0
Maximum value: 2147483647
Increasing the size of the special vnodes alias table allows you to create more special device files.
Obsolete System V attribute.
Obsolete.
Amount of time, in seconds, that a vnode can remain on the free list before it is deallocated.
Default value: 120 (seconds) for 32-MB or larger systems; 2 (seconds) for 24-MB systems
Minimum value: 0
Maximum value: 2147483647
You can increase the value of the vnode-age attribute to keep vnodes on the free list longer, which increases the possibility that the vnode will be successfully looked up.
You can modify this attribute at run time.
A value that enables (1) or disables (0) vnode deallocation.
Default value: 1 (enabled)
Enabling vnode deallocation decreases memory usage because it returns to the system the memory allocated to vnodes.
 

vm Subsystem Attributes

A value that enables (1) or disables (0) writing pages from the user page table to a crash dump.
Default value: 0 (disabled)
Setting this attribute to 1 provides more debugging information when a system crashes.
Number of 4-MB chunks of memory reserved at boot time for shared memory use.
A value that enables (1) or disables (0) a failure return by the shmget function under certain conditions. When this attribute is set to 1, the shmget function returns a failure if the requested segment size is larger than the value of the gh-min-seg-size attribute and if there is insufficient memory allocated by the gh-chunks attribute to satisfy the request.
Default value: 1 (enabled)
Size, in megabytes, of the segment in which shared memory is allocated from the memory reserved for shared memory, according to the value of the gh-chunks attribute.
Default value: 8 (MB)
A value that enables (1) or disables (0) separation of kernel stacks by unmapped guard pages. Guard pages are debugging aids that help isolate kernel stack corruption bugs caused by either overflowing or underflowing the kernel stack.
Default value: 1 (enabled)
Do not modify the default setting for this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation. A value that enables (1) or disables (0) caching of malloc memory on a per CPU basis.
Default value: 1
Do not modify the default setting for this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation.
Default value: 1 (on)
Do not modify the default setting for this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation.
Percentage of the secondary cache that is reserved for anonymous (nonshared) memory. Increasing the cache for anonymous memory reduces the cache space available for file-backed memory (shared).
Default value: 50 (percent)
Percentage of memory above which the UBC is only borrowing memory from the virtual memory subsystem. Paging does not occur until the UBC has returned all its borrowed pages.
Default value: 20 (percent)
Number of I/O operations (per second) that the virtual memory subsystem performs when the number of dirty (modified) pages in the UBC exceeds the value of the vm-ubcdirtypercent attribute.
Default value: 5 (operations per second)
Maximum percentage of physical memory that the UBC can use at one time.
Default value: 100 (percent)
Minimum percentage of physical memory that the UBC can use.
Default value: 10 (percent)
A value that enables (1) or disables (0) the ability of the task swapper to aggressively swap out idle tasks.
Default value: 0 (disabled)
Setting this attribute to 1 helps prevent a low-memory condition from occurring and allows more jobs to be run simultaneously. However, interactive response times are likely to be longer on a system that is excessively paging and swapping.
The number of asynchronous I/O requests per swap partition that can be outstanding at one time. Asynchronous swap requests are used for pageout operations and for prewriting modified pages.
Default value: 4
Size, in bytes, of the kernel cluster submap, which is used to allocate the scatter/gather map for clustered file and swap I/O.
Default value: 1048576 (bytes) (1 MB)
Maximum size, in bytes, of a single scatter/gather map for a clustered I/O request.
Default value: 65536 (bytes) (64 KB)
Number of times that the pages of an anonymous object are copy-on-write faulted after a fork operation but before they are copied as part of the fork operation.
Default value: 4 (faults)
Size, in bytes, of the kernel copy submap.
Default value: 1048576 (bytes, or 1 MB)
Percentage of physical memory allocated to the kernel heap. Many of the kernel data structures are allocated from the kernel heap. The kernel heap wires physical memory as the kernel data structures are allocated.
Default value: 7 (percent)
Minimum amount of time, in seconds, that a task remains in the inswapped state before it is considered a candidate for outswapping.
Default value: 1 (second)
Size , in bytes, of the kernel's map entry zone submap. Kernel map entries are reserved for both pageable and nonpageable regions of kernel virtual address space.
Default value: 16777216 (bytes) (16 MB)
Size of the map entry index.
Default value: 64
A large index can improve the entry lookup time, but may affect index rebalancing.
A value that enables (1) or disables (0) full indexing of map entries. Each map entry describes one unique disjoint portion of a virtual address space. If this attribute is set to 1, map entries are indexed in all processes.
Default value: 1 (enabled)
A value that, when multiplied by the value of vm-map-index-count, controls when the system creates a map entry index. When a process allocates map entries equal to the value of the vm-map-index-count attribute multiplied by the vm-map-index-hiwat attribute, the system creates a map entry index for fast lookups.
Default value: 4
A value that, when multiplied by the value of vm-map-index-count, controls when the system deletes a map entry index. When a process removes enough map entries from an index so that the number of entries is less than the value of the vm-map-index-count attribute multiplied by the value of the vm-map-index-lowat attribute, the system deletes the map entry index.
Default value: 2
A value that controls how frequently the map entry index is rebalanced. If the difference between the longest map entry list and the shortest map entry list is greater than the value of the vm-map-index-rebalance attribute, the system will rebalance the index.
Default value: 128
You can decrease the value of the vm-map-index-rebalance to improve the lookup time. However, this will increase the rate of rebalancing. If you increase the value of the vm-map-index-rebalance attribute, you will experience less rebalancing but have slower lookups.
Maximum number of map entries that any process can use at one time. Each map entry describes one unique disjoint portion of a virtual address space.
Default value: 200 (map entries)
Size, in bytes, of the largest pagein (read) cluster that is passed to the swap device.
Default value: 16384 (bytes) (16 KB)
Size, in bytes, of the largest pageout (write) cluster that is passed to the swap device.
Default value: 32768 (bytes) (32 KB)
Maximum amount of virtual address space, in bytes, that a user process can use at one time.
Default value: 1073741824 (bytes) (1 GB)
Maximum amount of memory, in bytes, that any user process can wire. (Paging activity generally increases as the amount of wired memory increases.)
Default value: 16777216 (bytes) (16 MB)
Base address of the kernel's virtual address space. The value can be either Oxffffffff80000000 or Oxfffffffe00000000, which sets the size of the kernel's virtual address space to either 2 GB or 8 GB, respectively. You may need to increase the kernel's virtual address space on very large (VL) systems (for example, systems with several gigabytes of physical memory and several thousand large processes).
Default value: 18446744071562067968 (2 to the power of 64)
The threshold value that stops page swapping. When the number of pages on the free list reaches this value, paging stops.
Default value: 1280 (pages)
The threshold value that starts page swapping. When the number of pages on the free page list falls below this value, paging starts.
Default value: 20 (pages)
The threshold value that begins hard swapping. When the number of pages on the free list falls below this value for five seconds, hard swapping begins.
Default value: 72 (pages)
The threshold value that determines when memory is limited to privileged tasks. When the number of pages on the free page list falls below this value, only privileged tasks can get memory.
Default value: 10 (pages)
The threshold value that begins swapping of idle tasks. When the number of pages on the free page list falls below this value, idle task swapping begins.
Default value: 74 (pages)
The threshold value that stops paging, When the number of pages on the free page list reaches this value, paging stops.
Default value: 128 (pages)
Size of the lock array that is used to synchronize access to vm_page kernel structures. Instead of locking each page structure, the virtual address is used to hash into the lock array. Adjust this value only if excessive lock contention occurs.
Default value: 64
Maximum number of pages that the vm subsystem will prewrite to swap space if it anticipates running out of memory. The prewritten pages are the least recently referenced (LRU) pages.
Default value: 256 (pages)
Number of text segments that can be cached in the segment cache. (Applies only if you enable segmentation)
Default value: 50 (segments)
The vm subsystem uses the segment cache to cache inactive executables and shared libraries. Because objects in the segment cache can be accessed by mapping a page table entry, this cache eliminates I/O delays for repeated executions and reloads.
Reducing the number of segments in the segment cache can free memory and help to reduce paging overhead. (The size of each segment depends on the text size of the executable or the shared library that is being cached.)
A value that enables (1) or disables (0) the ability of shared regions of user address space to also share the page tables that map to those shared regions.
Default value: 1 (enabled)
The number of synchronous I/O requests that can be outstanding to the swap partitions at one time. Synchronous swap requests are used for pagein operations and task swapping.
Default value: 128 (requests)
Maximum percentage of physical memory that can be dynamically wired. The kernel and user processes use this memory for dynamically allocated data structures and address space, respectively.
Default value: 80 (percent)
Total number of UBC I/O requests that can be outstanding at one time.
Default value: 256 (requests)
The percentage of pages that must be dirty (modified) before the UBC starts writing them.
Default value: 10 (percent)
The minimum number of pages to be available for file expansion. When the number of available pages falls below this number, the UBC steals additional pages to anticipate the file's expansion demands.
Default value: 24 (file pages)
The maximum percentage of UBC memory that can be used to cache a single file.
Default value: 10 (percent)
A threshold value that determines when the UBC starts to recognize sequential file access and steal the UBC LRU pages for a file to satisfy its demand for pages. This value is the size of the UBC in terms of its percentage of physical memory.
Default value: 50 (percent)
Maximum number of virtual pages within the address space for a process that can be given individual protection attributes (that is, protection attributes that differ from the protection attributes associated with the other pages in the address space).
Changing the protection attributes of a single page within a virtual memory region causes all pages within that region to be treated as though they had individual protection attributes. For example, each thread of a multithreaded task has a user stack in the stack region for the process in which they run. Because multithreaded tasks have guard pages (that is, pages that do not have read/write access) inserted between the user stacks for the threads, all pages in the stack region for the process are treated as though they have individual protection attributes.
If a stack region for a multithreaded task exceeds 16 KB pages, you may want to increase the value of the vm-vpagemax attribute.
Default value: 16384 (pages, or 16 KB pages)
Percentage of physical memory that is allocated to the kernel's zone submap. Many of the dynamically allocated kernel data structures are allocated out of zones that are located in the zone submap.
Default value: 0 (percent)
 

SEE ALSO

Commands: dxkerneltuner(8X), sysconfig(8), sysconfigdb(8)

System Configuration and Tuning


 

Index

NAME
DESCRIPTION
cm Subsystem Attributes
generic Subsystem Attributes
ipc Subsystem Attributes
proc Subsystem Attributes
vfs Subsystem Attributes
vm Subsystem Attributes
SEE ALSO

This document was created by man2html, using the manual pages.
Time: 02:43:12 GMT, October 02, 2010