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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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Sys::Statistics::Linux::MemStats(3pm)			User Contributed Perl Documentation		     Sys::Statistics::Linux::MemStats(3pm)

NAME
Sys::Statistics::Linux::MemStats - Collect linux memory information. SYNOPSIS
use Sys::Statistics::Linux::MemStats; my $lxs = Sys::Statistics::Linux::MemStats->new; my $stat = $lxs->get; DESCRIPTION
Sys::Statistics::Linux::MemStats gathers memory statistics from the virtual /proc filesystem (procfs). For more information read the documentation of the front-end module Sys::Statistics::Linux. MEMORY INFORMATIONS
Generated by /proc/meminfo. memused - Total size of used memory in kilobytes. memfree - Total size of free memory in kilobytes. memusedper - Total size of used memory in percent. memtotal - Total size of memory in kilobytes. buffers - Total size of buffers used from memory in kilobytes. cached - Total size of cached memory in kilobytes. realfree - Total size of memory is real free (memfree + buffers + cached). realfreeper - Total size of memory is real free in percent of total memory. swapused - Total size of swap space is used is kilobytes. swapfree - Total size of swap space is free in kilobytes. swapusedper - Total size of swap space is used in percent. swaptotal - Total size of swap space in kilobytes. swapcached - Memory that once was swapped out, is swapped back in but still also is in the swapfile. active - Memory that has been used more recently and usually not reclaimed unless absolutely necessary. inactive - Memory which has been less recently used and is more eligible to be reclaimed for other purposes. On earlier kernels (2.4) Inact_dirty + Inact_laundry + Inact_clean. The following statistics are only available by kernels from 2.6. slab - Total size of memory in kilobytes that used by kernel for data structure allocations. dirty - Total size of memory pages in kilobytes that waits to be written back to disk. mapped - Total size of memory in kilbytes that is mapped by devices or libraries with mmap. writeback - Total size of memory that was written back to disk. committed_as - The amount of memory presently allocated on the system. The following statistic is only available by kernels from 2.6.9. commitlimit - Total amount of memory currently available to be allocated on the system. METHODS
new() Call "new()" to create a new object. my $lxs = Sys::Statistics::Linux::MemStats->new; It's possible to set the path to the proc filesystem. Sys::Statistics::Linux::MemStats->new( files => { # This is the default path => '/proc', meminfo => 'meminfo', } ); get() Call "get()" to get the statistics. "get()" returns the statistics as a hash reference. my $stat = $lxs->get; EXPORTS
No exports. SEE ALSO
proc(5) REPORTING BUGS
Please report all bugs to <jschulz.cpan(at)bloonix.de>. AUTHOR
Jonny Schulz <jschulz.cpan(at)bloonix.de>. COPYRIGHT
Copyright (c) 2006, 2007 by Jonny Schulz. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. perl v5.14.2 2012-03-09 Sys::Statistics::Linux::MemStats(3pm)
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