How swap used in HPUX ?

sidharthmellam · November 17, 2011, 10:37am

Please clarify

Version: HP-UX <hostname> B.11.31 U ia64 unlimited-user license

Physical Configured is 36 GB

CPU info:
4 Intel(R) Itanium 2 9000 series processors (1.6 GHz, 24 MB)
533 MT/s bus, CPU version C2
12 logical processors

Memory: 36813 MB (35.95 GB)

Swap Configured is :

Glance output:

CPU  Util   S          SAU                                         U                                     | 63%   63%   63%
Disk Util   F                                                                                          F |100%  100%  100%
Mem  Util   S                SU                                                                      UF  |100%  100%  100%
Swap Util   U                                    UR                   R                                  | 64%   64%   64%

Am using SAP Application and Database, My question is ,

The swap usage remains used at 63% or 64% even though the Memory Utilization is 100% or 95% or 90%

Why the swap usage is not increasing in the system .

My understanding of swap usage is , when More Physical memory being used , automatically system should start using the swap configured in the system , in our case it is configured 61440 Mb , why the system is not utilizing the swap ?
it is always used at 63% or 64%

Thanks in advance

---------- Post updated at 09:07 PM ---------- Previous update was at 09:07 PM ----------

�

swapinfo -tam output is

Mb      Mb      Mb   PCT  START/      Mb
TYPE      AVAIL    USED    FREE  USED   LIMIT RESERVE  PRI  NAME
dev       61440   11907   49533   19%       0       -    1  /dev/vg00/lvol2
reserve       -   21636  -21636
memory    35016   27908    7108   80%
total     96456   61451   35005   64%       -       0    -

vbe · November 17, 2011, 10:50am

can you pass this command:

grep Phys /var/adm/syslog/syslog.log

sidharthmellam · November 18, 2011, 4:15am

Hello vbe / Moderator

Thanks For the Response,

Please Find the command output For grep Phys /var/adm/syslog/syslog.log

Aug 14 11:10:52 <hostname> vmunix: Class     Physmem              Lockmem              Swapmem
Aug 14 11:10:56 <hostname> vmunix:     Physical: 37697400 Kbytes, lockable: 29876104 Kbytes, available: 33429172 Kbytes

vbe · November 18, 2011, 4:29am

What don't you understand?

By the look of things, you have a swap logical volume defined twice the size of the RAM installed...
This would mean that you could load far more processes than what your real memory would allow ( since HPUX is a vitual memory system...).
My concern in your configuration is performance...

vbe · November 18, 2011, 4:50am

It will... if the system needs it...
I think what is not clear to you is how the Virtual System works:
In HPUX when you load a process, it will go to the VM first (that means swap device) to allocate the space needed, then loaded in memory - That space used is marked as RESERVED. Once all processes are running rather than waiste the unused memory it will be used as cache or SWAP (for it is far more faster the disk...). It is doing exactly that on your system: Your memory usage is almost maximum

sidharthmellam · November 18, 2011, 5:34am

: ) Thanks again For the Reply , Am an Application guy, But able to understand your reply ,

Now

For our system , at the present scenario, Whether to Configure more Physical Ram or swap usage ?

Now my question is

In the posted glance output , under what scenario the swap util Reaches 100% From the current value of 64%
Is the Following achievable

on the system what configurations has to be done , so that when usage of physical memory reaches 85% , at this point,
system should start using the swap configured , once this swap configured gets used 100% , than it should start consuming
the Remaining portion of the physical memory i e 15%

also unable to digest , how the swap used on HP UX

vbe · November 18, 2011, 7:48am

On your system I presume the kernel parameter swapmem_on is set to 1 (default value for 11.31) this means that the system can (and will ...) use up to 70% of your physical memory "AS" swap... after using all the physical memory as swap it will continue on de swap device...
In your case I find it frightening to see 19% of this time true swap used (meaning 12 GB contiguous disk space accessed...) has your system not slowed down?

compare to theses figures:

ran:/home/vbe $ swapinfo -tam
             Mb      Mb      Mb   PCT  START/      Mb
TYPE      AVAIL    USED    FREE  USED   LIMIT RESERVE  PRI  NAME
dev        2048       0    2048    0%       0       -    1  /dev/vg00/lvol2
dev        2060       0    2060    0%       0       -    1  /dev/esvg01/lvol2
dev        2048       0    2048    0%       0       -    1  /dev/esvg02/lvol2
reserve       -    1071   -1071
memory     5329    1560    3769   29%
total     11485    2631    8854   23%       -       0    -

Disk access / used = 0!

Noticed how I "balanced the load if ever it has to use the swap? ( It will write to the three in parallel multiplying the throughput...)

sidharthmellam · November 18, 2011, 8:02am

Dear vbe / Moderator

kudos for the reply ,

Now

shall I ask my OS Team to

Check swapmem_on whether set to 1 ,

if yes, what should be the correct value

whether shall i ask them to make it 0.

later shall we observe the swap usage for few days,

instead of , the way you configured on 3 /dev/vg00/lvol2 .......

Thanks in advance
Regards

vbe · November 18, 2011, 8:29am

Ask your admins if they cannot add at least an extra 8 GB RAM (Urgent...) but 12 GB would be preferable and 16 would be cool...
The best you can get out of your system is to stop it using swap!!
Swap means you have not enough memory to execute all you have loaded and so the system looses time by placing process not running at the time in swap device and when recalled again has to free memory by downloading yet more processes to be able to upload the one called etc...

sidharthmellam · November 21, 2011, 6:33am

Hi vbe/Moderator and All

But I read that , the parameter swapmem_on is an obsolete parameter on

HP Unix 11.31 ,

So whether it should be Considered as 1 or 0 ?

in the Following link

Regards

---------- Post updated at 05:03 PM ---------- Previous update was at 02:29 PM ----------

Hi Vbe,

is your system 11.31 or lesser ?

what is the value of swapmem_on in your system ?

&

in your configuration

Physical RAM = 5329 MB
Swap Configured on 3 dev is around 2048 MB,

But PCT Used For dev are all 0% , why ?

At the Time, when you have taken the above output ,

whether system is not at all using the swap configured ?

==================================================================

Coming to my system, yes swapmem_on is by default in 11.31 so we cannot make it disabled (0)

so according you , system will start using the 70% of physical memory as swap

1) How to stop the system from using the 70% of physical Ram , in HP Unix 11.31

2) Is it possible to make the system utilize the Swap Configured on dev , Fully

or

3) My system , yes it is slow down ,

if only increasing the physical Ram is the solution For my system

Than , what is the use of swap configuration ?

I dont know , How to go about this ?

Thanks and Regards

vbe · November 21, 2011, 8:37am

Swap is to allow a system to run more processes its memory can allow, by removing sleeping processes from memory (RAM) and move them to to virtual memory (disk) this process is called swapping. A well tuned machine should never or rarely swap or just a little.. You have 11 GB of permanent disk access on system disk...