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тАО02-28-2001 10:04 AM
тАО02-28-2001 10:04 AM
I am running an HP-UX 10.20 server in a production environment. It maintains a series of user objects, each one taking up a chunk of memory.
Every once in a while, when the number of objects get high, the memory will get used up and the machine will be unable to start any new processes of any kind.
When I do a swapinfo, I get the following ...
TYPE AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 1996 0 1996 0% 0 - 1 /dev/vg00/lvol2
reserve - 1996 -1996
memory 2887 2887 0 100%
When it gets to 100%, I cannot even do a remote login. My question is this, the swapinfo shows the memory swap as all used up, a device swap with 1996MB available, all 1996MB reserved, but none of it used.
Is the device swap being used, and if not where is the configuration error. I would have assumed that I should be able to run an almost unlimited number of objects and, if they got too high, they would simply start swapping to the hard drive more and slow the machine down, NOT take up all the available mem and choke the machine out...?
Thanks for any help you might give!
Mike
Solved! Go to Solution.
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тАО02-28-2001 10:20 AM
тАО02-28-2001 10:20 AM
Re: Memory choking out on HP-UX 10.20
The default for these is 50max/5min. But if you leave it at 50 for max than it's going to 50% of memory and put it as reserved off the top....I generally recommend setting this at 10max (..on certain conditions I have gone to 15) and 5min.
Just a thought,
/rcw
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тАО02-28-2001 10:59 AM
тАО02-28-2001 10:59 AM
SolutionDo a swapinfo -t (or -tm) and only look at the bottom line.
When a process start (and while it's running), if it asks for memory, the system allocates the same amount of swap space for it too should it need to be paged out. Therefore, although it may not be using the swap space, it's all be allocated (as swapinfo -tm) will show).
You can either increase swap space by using device swap, or if it's rare this occurs (and it's not actually using it), create some filesystem swap.
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тАО02-28-2001 11:11 AM
тАО02-28-2001 11:11 AM
Re: Memory choking out on HP-UX 10.20
Thanks for the input. I did the swapinfo -tm as you recommended, but it still leaves me confused. I think I do not understand the HP usage of device swap.
When I did the command, it did indeed show as AVAIL 2887MB of mem swap, and 1996MB of dev swap for a total of 4883. Under the USED heading it showed the dev swap as "0" used, the reserved as 1996MB and the mem used as 2460. Under the FREE heading it showed the dev swap as 1996 free, the reserve as -1996 and the mem as 427.
I understand the decive swap has 1996MB of space for swap, and it reserves ALL of it for the swap file (so that nothing else can be put there) but is the device swap (the reserved space) actually being used? And, if it is, why is the system choking out completely when the memory area gets full, instead of just slowing dramatically down because it is swapping more?
I have been searching the manuals for a description of the swap and how HP-UX uses it. If any of you know of a good tutorial, I would love to read it.
Thanks again!
Mike
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тАО02-28-2001 11:32 AM
тАО02-28-2001 11:32 AM
Re: Memory choking out on HP-UX 10.20
There is a good explaniation of 'psuedo swap' which is what this is in the file
/usr/share/doc/mem_mgm.txt
Althought the device swap isn't used, it's all be reserved and therefore you can't create more processes.
at hp-ux 11 (using elf executables), you can change this behaviour).
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тАО02-28-2001 11:51 AM
тАО02-28-2001 11:51 AM
Re: Memory choking out on HP-UX 10.20
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тАО06-20-2001 09:06 AM
тАО06-20-2001 09:06 AM
Re: Memory choking out on HP-UX 10.20
This turns on/off 'pseudoswap' (allows remaining RAM to serve as an electronic disk)!
If the output from 'swapinfo' shows sufficient device swap (1.5-2 times physical memory, or higher - depending on application requirements), you should be able to disable it and reclaim some memory for use by system/user processes.
Also, ensure that filesystem buffer cache isn't penalizing your system's virtual memory management capabilties (too small or too large can have a major impact on how the system behaves).
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тАО06-20-2001 09:51 AM
тАО06-20-2001 09:51 AM
Re: Memory choking out on HP-UX 10.20
Just change the kernel parameter swapmem_on to a 1 and now swapinfo -tm will make more sense, plus you'll be able to run more processes. Note that once you start using swap space, things will slow down.
Bill Hassell, sysadmin
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тАО06-21-2001 12:38 AM
тАО06-21-2001 12:38 AM
Re: Memory choking out on HP-UX 10.20
You must increase your swap space.
When you start new processes they ask to RESERVE memory and when it's available the system allocates it for them.
There is a rule for attributing swap space for system running production applications:
swap space = 3 or 4 times the amount of memory.