topic Re: Swap parameters in Operating System - HP-UX

Swap parameters

Jdamian — Tue, 09 Jan 2001 08:29:07 GMT

I tried to add a new swap area in my system by means of "swapon" and it reported an error message about "swchunk" and "swapchunks" kernel parameters.

Then I checked those parameters... I found that the swchunk value is 6144 but the help tells it would be an integer power of two, i.e., the possible values would be 2048,4096,8192,16384,...

I find nothing in "HP-UX Memory Management White Paper (Part II)" about this issue.

Is that true ? Is my swchunck value wrong ?

If it is wrong and needs an integer power of 2, what value is used now on my system ?
Does it impact my system performance ?

Thanx in advance

Re: Swap parameters

Dan Hetzel — Tue, 09 Jan 2001 10:32:07 GMT

Hi,

swchunk defaults to 2048 and can be adjusted to 16384.
The value you're using now seems a bit weird...
You should probably adjust it to 8192.

Total swap space is defined by:
swchunk * maxswapchunks * DEV_BSIZE
where DEV_BSIZE is 1024 bytes.

Here is a document that may help you in adjusting all kernel parameters:
http://docs.hp.com/hpux/onlinedocs/os/KCparams.OverviewAll.html

Best regards,

Dan

Re: Swap parameters

Darrel Louis — Tue, 09 Jan 2001 10:40:58 GMT

http://www.docs.hp.com//hpux/onlinedocs/os/KCparams.OverviewAll.html

http://www.docs.hp.com//hpux/onlinedocs/os/KCparam.SwChunk.html
Minimum : 2048
Maximum : 16384
Default : 2048

Check the url above for further info.

Regards

Darrel

Re: Swap parameters

James R. Ferguson — Tue, 09 Jan 2001 14:11:41 GMT

Hi:

Yes, the value of 'swchunk' should be a power of two. 'swchunk' defines the "chunk" size, or minimum unit involved in swap activity. Thus, 'swchunk' is the smallest unit of allocation of device or filesystem swap. 'swchunk's are divided into DEV_BSIZE bytes. Since DEV_BSIZE is a fixed constant of 1024 bytes which cannot be changed, 'swchunk' must be a multiple of 1024 -- a power-of-two.

...JRF...

Re: Swap parameters

Andy Monks — Wed, 17 Jan 2001 08:52:18 GMT

Never change the swchuck parameter (which does have to be a power of 2).

Only change maxswapchunks, which is what the message really suggests doing.