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Man page of sys_attrs
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
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using the manual pages.
Time: 02:43:05 GMT, October 02, 2010