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Full Discussion: Memory usage in AIX server
Operating Systems AIX Memory usage in AIX server Post 302843466 by rbatte1 on Tuesday 13th of August 2013 11:54:35 AM
Old 08-13-2013
Don't panic!

AIX is very good at keeping memory full with all sorts of things it believes will be useful. If something is not needed now, there is no reason to actually scrub memory unless another process is allocated that address to work in. I used to worry about this too. It can (as you suggest) be used for all sorts of caching. It is faster than reading from the disk, but there is no point in paging it out, so it just gets lost if not used. When a process then needs the data, it is just read from disk as normal, which is no different than paging back in (unless you have wildly different performance disks) but to use the paging, it would have to keep a record that it existed etc., so it's more effort to page this kind of thing.


Basically, if the server is not paging, then it is fine. Smilie


There used to be a rule of thumb for double paging space for your RAM. Then that changed (even less formally if that's possible) to double RAM for the first 2Gb, then 1Gb for the rest of your RAM allocation.

Of course, what you really need to estimate is the total space you will need and balance the cost against the speed of real memory. Beyond what you can justify paying for, allocate paging to cover it, and a bit more to be sure. Very inexact though. Have some sort of monitor that check paging space, either have a regular look with lsps -a or vmstat, sar or other tools just to keep a check on how much you are really using.

If you are paranoid about crashing the server, allocate lots extra paging space, but don't try to grow /dev/hd6. If you succeed, you will never be able extract it without considerable effort. Smilie

If you allocate 2Gb chunks as paging00, paging01, paging02 ....etc., then when your service is settled, you can work out how many to remove.

If you can space a disk, create a dedicated VG for them in the short term, rather than filling up rootvg and making DR recovery a problem.



I hope that this helps,

Robin
Liverpool/Blackburn
UK
 

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SWAPON(8)						     Linux Programmer's Manual							 SWAPON(8)

NAME
swapon, swapoff - enable/disable devices and files for paging and swapping SYNOPSIS
/sbin/swapon [-h -V] /sbin/swapon -a [-v] [-e] /sbin/swapon [-v] [-p priority] specialfile ... /sbin/swapon [-s] /sbin/swapoff [-h -V] /sbin/swapoff -a /sbin/swapoff specialfile ... DESCRIPTION
Swapon is used to specify devices on which paging and swapping are to take place. Calls to swapon normally occur in the system multi-user initialization file /etc/rc making all swap devices available, so that the paging and swapping activity is interleaved across several devices and files. Normally, the first form is used: -h Provide help -V Display version -s Display swap usage summary by device. Equivalent to "cat /proc/swaps". Not available before Linux 2.1.25. -a All devices marked as ``swap'' swap devices in /etc/fstab are made available. Devices that are already running as swap are silently skipped. -e When -a is used with swapon, -e makes swapon silently skip devices that do not exist. -p priority Specify priority for swapon. This option is only available if swapon was compiled under and is used under a 1.3.2 or later kernel. priority is a value between 0 and 32767. See swapon(2) for a full description of swap priorities. Add pri=value to the option field of /etc/fstab for use with swapon -a. Swapoff disables swapping on the specified devices and files. When the -a flag is given, swapping is disabled on all known swap devices and files (as found in /proc/swaps or /etc/fstab). NOTE
You should not use swapon on a file with holes. Swap over NFS may not work. SEE ALSO
swapon(2), swapoff(2), fstab(5), init(8), mkswap(8), rc(8), mount(8) FILES
/dev/hd?? standard paging devices /dev/sd?? standard (SCSI) paging devices /etc/fstab ascii filesystem description table HISTORY
The swapon command appeared in 4.0BSD. Linux 1.x 25 September 1995 SWAPON(8)
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