proper settings for swap

[Randy_9]

Question:
I have 2GB of RAM and a 4 GB swap device,
the kernel setting for maxdsiz and maxswapchunks are:
# sysdef | grep -i maxdsiz
maxdsiz 503866 - 0-503866 Pages -
maxdsiz_64bit 524288 - 1024-1073479679 Pages -
# sysdef | grep -i maxswapchunks
maxswapchunks 2048 - 1-16384 -

Are these set to the optimal level to take advantage of the RAM and swap, do you
see a problem?

Thanks,

Randy

[Patrick Wallek · Accepted solution]

maxswapchunks controls the MAXIMUM AMOUNT of swap you can have configured on your system. So if you have 4GB configured and it is active and available (ie. No errors when the system boots about not being able to active swap) then that parameter is good. It controls nothing else with regards to usage of swap space or RAM.
Maxswapchunks info -
http://docs.hp.com/hpux/onlinedocs/939/KCParms/KCparam.MaxSwapChunks.html

maxdsiz and maxdsiz_64 specify the maximum data segment size, in bytes, for an executing process. So that is one of the controls to keep a process from using too much RAM. See here for more info on maxdsiz* parameters - http://docs.hp.com/hpux/onlinedocs/939/KCParms/KCparam.MaxDsiz.html

You can also look here for info on all configurable kernel parms -
http://docs.hp.com/hpux/onlinedocs/939/KCParms/KCparams.OverviewAll.html

Is there some problem you are having that is leading to these questions?

[Randy_9]

Patrick,

Some developers were running into
problems with swap ( they weren't
too detailed ) so I thought I would
double the current settings.

Thank you,

Randy

[Kevin Wright]

There is no reason to double the maxswapchunks parameter unless you plan on adding more swap. This simply determines how much swap is allowed to be configured on your system. I usually set it to the max when I first build a server and be done with it.

check your swap usage with swapinfo -tam.

[Steven E. Protter]

When developers get errors and trace them back to swap or lack of memory, this is were we start:

swapminfo -tam

This shows if were are really using all or most of our swap.

Now: If you have high utilization and swap is already twice RAM don't add any more swap. You'll just slow your system down.

In that scenario you need memory.

If however you need general swap guidelines:

I'm a member of the A. Clay Stephenson school of swap.
I set one swap area, as small as possible as primary, sometimes as small as half system ram. I then set a secondary swap area to cover the rest.

This gets me very fast performance during low and medium system loads.

To pick the overall number: between 1.5 and 2.0 times RAM. The more RAM you have the less you need to be in the 2.0 multiple neighborhood.

SEP