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Question about memory reservation beyond (maxswapchunks * swchunk * 1k) on 11.23

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ricardor_1
Frequent Advisor

Question about memory reservation beyond (maxswapchunks * swchunk * 1k) on 11.23

Hello everyone,

I understand I still need to reserve swap for every allocated memory under 11.23. However, how does it work beyong the maximum supported swap space?

We have 38 GB of physical RAM and have setup the same amount of RAM (device+swapmem). We are afraid we won´t be able to use all the available physical RAM due to the reservation behavior.

Thank you.
8 REPLIES
Steven E. Protter
Exalted Contributor

Re: Question about memory reservation beyond (maxswapchunks * swchunk * 1k) on 11.23

Shalom,

In general I disable formulas like this because they do not work in the real world.

swapinfo -tam

Please post.

In a system with this much RAM, if total available swap space is equal to memory you should be able to use all available physical ram.

I would not use this formula though as stated above.

SEP
Steven E Protter
Owner of ISN Corporation
http://isnamerica.com
http://hpuxconsulting.com
Sponsor: http://hpux.ws
Twitter: http://twitter.com/hpuxlinux
Founder http://newdatacloud.com
ricardor_1
Frequent Advisor

Re: Question about memory reservation beyond (maxswapchunks * swchunk * 1k) on 11.23

Hi,

Thank you, but the formula was not inserted anywhere, it´s the definition of swap usage under HP-UX according to http://docs.hp.com/en/939/KCParms/KCparam.MaxSwapChunks.html

(Actually: maxswapchunks times swchunk times DEV_BSIZE)

The swapinfo follows:

Mb Mb Mb PCT START/ Mb
TYPE AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 20480 0 20480 0% 0 - 1 /dev/vg00/lvol2
dev 20480 0 12288 0% 0 - 1 /dev/vg00/swap1
reserve - 25018 -25018
memory 38863 24846 14017 64%
total 79823 49864 21767 62% - 0 -
ricardor_1
Frequent Advisor

Re: Question about memory reservation beyond (maxswapchunks * swchunk * 1k) on 11.23

Just to be more clear, I want to confirm if:

Being limited to the maximum supported swap space at 32 GB, without changing swapchunks (which is not recommended), will I be able to reserve and use up to 38 GB, which is my physical RAM?

Thanks.
Dennis Handly
Acclaimed Contributor
Solution

Re: Question about memory reservation beyond (maxswapchunks * swchunk * 1k) on 11.23

>will I be able to reserve and use up to 38 GB, which is my physical RAM?

You don't need device swap to access your RAM. You have pseudo-swap enabled.
Your total swap is 80 Gb. You have reserved 25 Gb of device swap but not paging to it yet.
ricardor_1
Frequent Advisor

Re: Question about memory reservation beyond (maxswapchunks * swchunk * 1k) on 11.23

>>will I be able to reserve and use up to 38 GB, which is my physical RAM?

>You don't need device swap to access your RAM. >You have pseudo-swap enabled.
>Your total swap is 80 Gb. You have reserved 25 >Gb of device swap but not paging to it yet.

Thanks, so maxswapchunks and swapchunks only limits the amount of device swap space and the pseudo-swap adds to the amount of max reserved space. That answers my question.

Thank you again.

BTW: If you look at the FREE space on /dev/vg00/swap1, you´ll notice that, even though they´ve created two 20 GB swap devs, only 20+12GB are available.
Dennis Handly
Acclaimed Contributor

Re: Question about memory reservation beyond (maxswapchunks * swchunk * 1k) on 11.23

>If you look at the FREE space on /dev/vg00/swap1, you'll notice that, even though they've created two 20 GB swap devs, only 20+12GB are available.

That's probably your (maxswapchunks * swchunk) limitation.

The formula that SEP was probably referring to was one there you need N X RAM for swap.
This changes when RAM is very large.
Steven E. Protter
Exalted Contributor

Re: Question about memory reservation beyond (maxswapchunks * swchunk * 1k) on 11.23

Yes Dennis, that is the formula causing the limitation in available swap space. Though it probably will not limit use of physical ram, that depends on what the application tries to reserve.

Better off getting rid of the formula so if you need it all swap is available.

SEP
Steven E Protter
Owner of ISN Corporation
http://isnamerica.com
http://hpuxconsulting.com
Sponsor: http://hpux.ws
Twitter: http://twitter.com/hpuxlinux
Founder http://newdatacloud.com
Dennis Handly
Acclaimed Contributor

Re: Question about memory reservation beyond (maxswapchunks * swchunk * 1k) on 11.23

>SEP: Better off getting rid of the formula so if you need it all swap is available.

That (maxswapchunks * swchunk) formula is hardcoded in the 11.11 kernel.
(I don't see maxswapchunks on 11.23 and it looks like it is hardcoded to 16384.)

That rule of thumb about device swap and RAM can be changed.