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memory_trolling(5)					    memory_trolling(5)

NAME
       memory_trolling	-  Proactively	locates	 and scrubs correctable memory
       errors

SYNOPSIS
       /etc/sysconfigtab

       vm: vm_troll_percent =  percent_rate

DESCRIPTION
       The operating system handles memory errors with a  just-in-time	scrub‐
       bing  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 per‐
       cent  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 dur‐
       ing 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_per‐
       cent (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	 supe‐
       ruser  (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
       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 perfor‐
       mance overhead, use the following procedure: Log in as root  or	become
       superuser.   Choose a time when the system is idle and disable the mem‐
       ory troller using the following command:

	      #	 /sbin/sysconfig -r vm vm_troll_percent=0 To establish a  per‐
	      formance	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 fol‐
	      lowing 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  per‐
       formance	 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.

MESSAGES
   Configuration Messages
       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
       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 mes‐
	      sages 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
       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.

EXAMPLES
       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 exe‐
	      cution 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/syscon‐
	      figtab 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

FILES
       The  configuration  database  file  in  which  you specify the value of
       vm_troll_percent under the vm attributes. See the sysconfigtab(4)  ref‐
       erence  page for more information.  The command that you use to dynami‐
       cally 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.

SEE ALSO
       Commands: sys_attrs_vm(5), sysconfig(8), sysconfigdb(8), and vmstat(1)

							    memory_trolling(5)
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