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memory_trolling(5)
Contents
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memory_trolling - Proactively locates and scrubs correctable
memory errors
/etc/sysconfigtab
vm: vm_troll_percent = percent_rate
The operating system handles memory errors with a just-intime
scrubbing model, where correctable errors are
scrubbed when encountered by the operating system or an
application. To enhance this capability, a trigger mechanism,
called the memory troller proactively locates and
scrubs correctable memory errors. The memory troller systematically
reads each memory location. If it discovers a
correctable memory error, it triggers the just-in-time
scrubbing mechanism.
Since the memory troller reads all memory available to the
operating system, it might also discover uncorrectable
memory errors, which would lead to a unrecoverable machine
check. To avoid this, the operating system recognizes that
the machine check resulted from memory trolling, dismisses
the error, and continues normal operation. The memory
troller then causes the memory page containing the uncorrectable
error to be marked as a bad page. If the bad page
is free (or when it becomes free) it is then mapped out so
it will not be reused.
Enabling, Disabling, and Tuning Memory Trolling
For systems supported by the memory troller, use the
vm_troll_percent variable to enable, disable, and tune the
trolling rate. This parameter is part of the kernel's vm
subsystem. The trolling rate is expressed as a percentage
of the system's total memory trolled per hour and can be
changed at any time. Valid troll rate settings are as follows:
This value is used by default if you do not specify
any value for vm_troll_percent. At this default rate, each
8 kilobyte memory page is trolled once every 24 hours. A
value of zero disables the memory troller. The troll rate
is set to the specified percentage of memory to troll
per hour. For example, a 50 percent troll rate reads half
the total memory in one hour. After all memory is read,
the troller starts a new pass at the beginning of memory.
Any value greater than 100 percent invokes one-pass accelerated
trolling. All memory is trolled at a rate of
approximately 6000 8 kilobyte pages per second, then
trolling is disabled. This mode is intended for trolling
all memory quickly during off peak hours. For example,
on a GS320 system with 32 processors and 128 gigabytes of
memory, one-pass accelerated trolling takes approximately
five minutes.
Use the following command to display the current value of
vm_troll_percent (the troll rate):
# /sbin/sysconfig -q vm vm_troll_percent
You can override the default troll rate by adding the
following lines to the /etc/sysconfigtab file:
vm: vm_troll_percent=percent_rate
The percent_rate variable is the troll rate as described
previously. Use the sysconfigdb command to add entries to
the /etc/sysconfigtab file, as described in the sysconfigdb(8) reference page. The new rate takes effect on the
next system boot.
You can enable, disable, or change the troll rate at any
time using the following command:
# /sbin/sysconfig -r vm vm_troll_percent=percent_rate
The variable is the troll rate as described previously.
Only the superuser (root) or a user authorized by division
of privileges (dop) can use this command. (Refer to the
dop(8) reference page for information on sharing superuser
privileges.)
See MESSAGES for information on configuration messages
Controlling the Use of System Resources [Toc] [Back]
Low trolling rates, such as the 4 percent default, have
negligible impact on system performance. Processor usage
for memory trolling increases as the troll rate is
increased. To approximate the performance overhead, use
the following procedure: Log in as root or become superuser.
Choose a time when the system is idle and disable
the memory troller using the following command:
# /sbin/sysconfig -r vm vm_troll_percent=0 To
establish a performance baseline, run the following
command with the memory troller disabled:
# vmstat 1 ...cpu... ...us sy id... ... 1 1
98... In the command output, note the system time,
labeled sy under the cpu heading. Adjust the value
of vm_troll_percent using the following command:
# /sbin/sysconfig -r vm vm_troll_percent=percent_rate
Repeat step 3 and note any change in the value of
sy under the cpu heading.
A system time (sy) increase of one or less represents negligible
performance cost. Repeat the procedure, adjusting
the percent value of vm_troll_percent until the performance
cost is acceptable.
For example, a GS320 system with 32 processors and 128 GB
of memory will show approximately 25 percent of system
time during one-pass accelerated trolling. The same system
at the 4 percent default troll rate will show one percent
or less system time.
Configuration Messages [Toc] [Back]
If the memory troller does not support your system, the
following error is displayed on your terminal when you
attempt to configure the memory troller using
/sbin/sysconfig:
vm_configure: Memory Trolling not supported on this system.
You can disable trolling using the following command:
# /sbin/sysconfig -r vm vm_troll_percent=0
The following warning message is displayed on your terminal
when the preceding command is executed:
vm_configure: shutting down memory troller. [WARNING:
disabling the memory troller is not recommended on this
system.]
This message notifies you that permanently disabling memory
trolling is not recommended.
Informational Messages [Toc] [Back]
The following messages provide information about events
associated with memory troller operation. These messages
do not indicate a failure in the memory troller: If a memory
page containing a uncorrectable error was located by
the memory troller and the bad page will be mapped out,
the following message is displayed:
Memory Troller: bad page found (address =
0x################) In addition to the bad page
found... message, machine check messages similar
to the following are displayed on the system's console
when the memory troller encounters a bad page:
25-Mar-2000 17:24:25 [700] CPU machine check/exception
- CPU 0 25-Mar-2000 17:24:25 [700] CPU machine
check/exception - CPU 18
These messages come from the event notification
subsystem. They indicate that the machine checks
resulting from the memory troller reading the bad
page have been entered into the binary error log.
Error Messages [Toc] [Back]
If any of the following error messages are displayed on
the console terminal, a malfunction has occurred in the
memory troller and you must contact your technical support
organization. VM_CONFIGURE: Memory Trolling is currently
disabled on this system
The memory troller has been disabled due to a fatal
error. adjust_troll_quantity: null MAD pointer,
disabling troller
A fatal internal error has occurred, the troller is
disabled. adjust_troll_quantity: invalid
troll_percent 0 defaulting to 4 percent
The troller is active, but the troll rate is zero.
The troller continues operating, but at the default
troll rate. This is a serious error. vm_memory_troller:
CPU # vmmt_get_mad() failed, disabling
troller
A fatal internal error has occurred, the troller is
disabled. vm_memory_troller: MAD # invalid state
[#], shutting down
A fatal internal error has occurred, the troller is
disabled.
The following examples demonstrate typical command use and
settings for the memory troller: To schedule one-pass
accelerated trolling at off peak hours, use the following
procedure: Create a shell script named
/usr/local/fast_troll.sh containing the following lines:
#!/sbin/sh
/sbin/sysconfig -r vm vm_troll_percent=101 Using
the following commands, set the file owner and permissions
of /usr/local/fast_troll.sh:
# chown root /usr/local/fast_troll.sh # chmod 744
/usr/local/fast_troll.sh Use the cron facility to
schedule execution of the shell script as root user
at the desired time. (Refer to the cron(8) reference
page for more information.) The following
command demonstrates how you can set trolling at a
more aggressive rate of 50 percent per hour:
# /sbin/sysconfig -r vm vm_troll_percent=50
As such dynamic changes are not recorded in the
/etc/sysconfigtab file, this setting will not persist
across a reboot. The following method
describes how you use a stanza file to change the
value of vm_troll_percent to 10 so that the change
is updated in the kernel immediately and also persists
across a reboot: Create a stanza file containing
the following lines:
vm: vm_troll_percent=10
Save this file as /tmp/vm_troller.stanza. Use the
following command to merge the stanza in the
/etc/sysconfigtab file:
#/sbin/sysconfigdb -a -f /tmp/vm_troller.stanza vm
The configuration database file in which you specify the
value of vm_troll_percent under the vm attributes. See the
sysconfigtab(4) reference page for more information. The
command that you use to dynamically set the value of
vm_troll_percent under the vm attributes in the
/etc/sysconfigtab file. See the sysconfig(8) reference
page for more information.
Commands: sys_attrs_vm(5), sysconfig(8), sysconfigdb(8),
and vmstat(1)
memory_trolling(5)
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