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тАО10-10-2012 05:31 AM - edited тАО10-10-2012 05:35 AM
тАО10-10-2012 05:31 AM - edited тАО10-10-2012 05:35 AM
Free physical memory
I should know this but thats senility kicking in
from the output below should I be reading it that there is currently 12gb of physical memory available to the system and 4.3gb is used.
:/ # swapinfo -mat
Mb Mb Mb PCT START/ Mb
TYPE AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 12288 0 12288 0% 0 - 1 /dev/vg00/lvol2
dev 12288 0 12288 0% 0 - 1 /dev/vg00/lvswap1
reserve - 19659 -19659
memory 16335 4331 12004 27%
total 40911 23990 16921 59% - 0 -
Also for pseudo swap (same server) does the below output from glance mean that 4.2gb of physical memory currently is being used as swap? i'm trying to make sense of the output from swapinfo with the glance output to see what actual physical memory is free. (Looking into reallocation memory from this vpar to another)
Swap Device Type Avail Used Priority
--------------------------------------------------------------------------------
/dev/vg00/lvol2 device 12.0gb 0mb 1
/dev/vg00/lvswap1 device 12.0gb 0mb 1
pseudo-swap memory 16.0gb 4.2gb -1
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тАО10-10-2012 10:20 AM
тАО10-10-2012 10:20 AM
Re: Free physical memory
>mean that 4.2gb of physical memory currently is being used as swap?
That's what I read too. Are you measuring this when the system is loaded?
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тАО10-11-2012 12:09 AM
тАО10-11-2012 12:09 AM
Re: Free physical memory
It is pseudo-swap, so it is just a counter of reserved memory -
So it doesn't get 4.2G of your memory, it just mean that the total allocated reserved memory by application is 4.2G
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тАО10-11-2012 04:47 AM
тАО10-11-2012 04:47 AM
Re: Free physical memory
From the document titled "Memory usage (What is using all of the memory?)" by Eric Herberholz at HP:
-----
The memory line is infamously misleading and does not refer to acual physical memory use!!!! Rather it is the size of pseudoswap, which happens to be calculated to be 75% of the size of RAM (a.k.a. memory.) As the name ("pseudo") implies, it does NOT exist. Pseudoswap is enabled by default with the kernel parameter swapmem_on(5) set to 1. Don't worry about this line, just look at the total line for total used and sometimes it's interesting to look at the device PCT USED as an indication of how much swapping has occurred since the box was last rebooted.
-----
And the swapmem_on(5) man page further explains the memory allocation with pseudo-swap:
In previous versions of HP-UX, system configuration required sufficient physical swap space for the maximum possible number of processes on the system. This is because HP-UX reserves swap space for a process when it is created, to ensure that a running process never needs to be killed due to insufficient swap. This was difficult, however, for systems needing gigabytes of swap space with gigabytes of physical memory, and those with workloads where the entire load would always be in core. This tunable was created to allow system swap space to be less than core memory. To accomplish this, a portion of physical memory is set aside as 'pseudo-swap' space. While actual swap space is still available, processes still reserve all the swap they will need at fork or execute time from the physical device or file system swap. Once this swap is completely used, new processes do not reserve swap, and each page which would have been swapped to the physical device or file system is instead locked in memory and counted as part of the pseudo-swap space.
So, if your vPar has 16 GB of pseudo-swap, it means it probably has (16 GB / 0.75 =) about 21 GB of actual physical RAM assigned to it.
You did not specify the version of HP-UX you have. But if you have Glance available, press "m" in Glance to get the Memory Report page. The bottom of the page has three lines that have a lot of memory statistics that should be useful to you. It includes Phys Mem (amount of RAM on the system), and Free Mem (which is what you are looking for).
But if Free Mem is near zero, you should also pay attention to the size of the Buffer Cache (or File Cache in 11.31): unless the caches have been restricted, they may claim large chunks of memory that is not otherwise occupied. If memory is needed for applications and there is no free memory available, the OS will by default automatically shrink the caches as required. (Although in at least 11.23 and older, the buffer cache auto-shrinking was so slow that it was better to restrict the cache to a sensible maximum size in the first place.)
So, start by figuring a sensible size for buffer/file caches on your system, and then look at the cache + free memory numbers. If there is lots of free memory, you can clearly take some memory away from the vPar; but if there is not much free memory but the caches are excessively large, that is also a sign that you can take away some memory.
Just make sure you leave at least some space for caching, or your disk I/O performance will suffer.
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тАО10-11-2012 09:04 AM
тАО10-11-2012 09:04 AM
Re: Free physical memory
Ok just trying to get my head round this, what i'm after is how to interpret what amount is being used by say system processes, user processes, etc and more importantly what physical memory is free.
I may have misunderstood but from the output below from another vpar thats under load, should I be reading it that there is only 497mb free of physical memory. Also 4.0gb is being used apparently by pseudo swap, thats just reserved not actually in use? And is this fixed or dynamic, ie if the system needs more memory will it reduce the pseudo swap used and start swapping to disk. Apologies but the more I dig the more confused I get!
HP-ux version is 11.23
# swapinfo -mat
Mb Mb Mb PCT START/ Mb
TYPE AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 16336 0 16336 0% 0 - 1 /dev/vg00/lvol2
dev 32924 2210 30714 7% 0 - 0 /dev/vgswap/lvswap
reserve - 22719 -22719
memory 15537 4121 11416 27%
total 64797 29050 35747 45% - 0 -
Swap Device Type Avail Used Priority
--------------------------------------------------------------------------------
/dev/vg00/lvol2 device 16.0gb 0mb 1
/dev/vgswap/lvswap device 32.2gb 2.2gb 0
pseudo-swap memory 15.2gb 4.0gb -1
Glance C.04.70.001 16:45:52 * ia64 Current Avg High
--------------------------------------------------------------------------------
CPU Util S SRU U | 31% 33% 42%
Disk Util FF | 3% 5% 11%
Mem Util S SU U | 97% 97% 97%
Swap Util U UR R | 45% 45% 45%
--------------------------------------------------------------------------------
MEMORY REPORT Users= 2
Event Current Cumulative Current Rate **bleep** Rate High Rate
--------------------------------------------------------------------------------
Page Faults 3629 22385 648.0 928.8 1742.8
Page In 344 1764 61.4 73.1 597.6
Page Out 0 0 0.0 0.0 0.0
KB Paged In 1.3mb 6.9mb 245.7 292.7 1641.6
KB Paged Out 0kb 0kb 0.0 0.0 0.0
Reactivations 0 0 0.0 0.0 0.0
Deactivations 0 0 0.0 0.0 0.0
KB Deactivated 0kb 0kb 0.0 0.0 0.0
VM Reads 1198 5948 213.9 250.9 293.2
VM Writes 0 0 0.0 0.0 0.0
Total VM : 19.1gb Sys Mem : 4.2gb User Mem: 9.7gb Phys Mem : 16.0gb
Active VM: 9.0gb Buf Cache: 1mb Free Mem: 487mb FileCache: 1.5gb
MemFS Blk Cnt: 0 MemFS Swp Cnt: 0 Page 1 of 1
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тАО10-11-2012 01:14 PM
тАО10-11-2012 01:14 PM
Re: Free physical memory
>if your vPar has 16 GB of pseudo-swap, it means it probably has (16 GB / 0.75 =) about 21 GB of actual physical RAM assigned to it.
Unfortunately this 75% figure is stale and no longer valid. I've also heard it's 7/8.
I think on 11.31, the total is closer to the real memory size.
>should I be reading it that there is only 497mb free of physical memory.
Yes, that's what it says. Also pseudo-swap memory is 15.2 vs 16 for physical.
>4.0gb is being used apparently by pseudo swap, that's just reserved not actually in use?
No, it is always used, never just "reserved".
>if the system needs more memory will it reduce the pseudo swap used and start swapping to disk.
It will never reduce pseudo swap, unless a process exits or releases memory. It will increase and if still not enough, just start swapping additional pages to disk.
It may reduce pseudo swap if the kernel needs more resident memory?
Hmm. If something was swapped out and was brought back, that can no longer be counted in the used pseudo swap, otherwise it would be counted twice.
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тАО10-12-2012 03:27 AM
тАО10-12-2012 03:27 AM
Re: Free physical memory
So there's 4gb of the memory being used by pseudo, 11.6gb ish being used by the system/apps and only 497mb free of physical memory in the case above?
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тАО10-12-2012 03:53 AM
тАО10-12-2012 03:53 AM
Re: Free physical memory
>So there's 4gb of the memory being used by pseudo
I would say that's double counting.
Sys Mem: 4.2gb User Mem: 9.7gb Free Mem: 487mb FileCache: 1.5gb
This is pretty close to 16 gb,