6GB of memory missing

[mlcboy01]

Greetings,

I have an AIX 4.3.3 ML10, Dual Processor, 8GB physical memory server

lsattr -l sys0 -E
realmem 8388608 Amount of usable physical memory in Kbytes

On boot, I'm told by ipcs -pmb:

Shared Memory:
m 0 0x5800484b --rw-rw-rw- root system 134217728 13676 13676
m 1 0x47003028 --rw-r--r-- imnadm imnadm 48 22192 22192
m 2 0x58003028 --rw-r--r-- imnadm imnadm 4096 22192 22192
m 3 0x4d003028 --rw-r--r-- imnadm imnadm 4096 22192 22192
m 4 0x49003028 --rw-r--r-- imnadm imnadm 4096 22192 22192
m 5 0x50003028 --rw-r--r-- imnadm imnadm 3222 22192 22192
m 6 0x4500302f --rw-rw-rw- imnadm imnadm 96 25542 25542
m 7 0x4300302f --rw-rw-rw- imnadm imnadm 97708 25542 25542
m 8 0x4200302f --rw-rw-rw- imnadm imnadm 36028 25542 25542
m 9 0x4100302f --rw-rw-rw- imnadm imnadm 42148 25542 25542
m 10 0x4400302f --rw-rw-rw- imnadm imnadm 2844 25542 25542


And yet, vmstat tells me:

#> vmstat
kthr memory page faults cpu
----- ----------- ------------------------ ------------ -----------
r b avm fre re pi po fr sr cy in sy cs us sy id wa
1 1 25399 1972498 0 0 0 0 0 0 728 2989 1063 2 2 87 9

(Hard to read, but the "fre" column says "1972498" 1.9gb, yes?

8.0gb - 1.9gb = 6.1 minus 134mb (that ipcs claims I'm using for the "system) = 5966MB

So where did the other 5.9 gigs plus of memory go?

 

[DSMARWAY]

hi ,

fre in vmstat, from what i understand is the real memory left after the amount it uses has been cached .

From what i understand about memory ( welcome to sugestions) is that firstly real memory gets used
then if it runs out of real memory , virtual memory ( swap space) gets used .
SO the fre means how much free real memory is available after what it requires gets cached by the system?

Have you got the nmon utility installed ?

if so run nmon , it will show you how much real memory is used and free , and how much Virtual memory is used and free?

 

[unixtechie]

vmstat are in pages of 4096.

 

[mlcboy01]

DSMARWAY and unixtechie,

Thanks for the replies. I did download and run the nmon utility, and it did in fact confirm what we believed about the memory usage:

% Used 100.0% 26.3% to Paging Space 0.0 0.0 numperm 73.0%
% Free 0.0% 73.7% to File System 0.0 4.0 minperm 20.0%
MB Used 8189.1MB 1076.7MB Page Scans 0.0 maxperm 80.0%
MB Free 2.9MB 3019.3MB Page Cycles 0.0 minfree 120
Total(MB) 8192.0MB 4096.0MB Page Reclaim 0.0 maxfree 128

It makes me very nervous to watch these memory stats fluctuate from 1.9gb free on startup (with the Oracle 9i databases on-line, no users) to 0.5mb free with less than 5 users attached to the databases(s)

Where has the memory gone?

 

[Morsing]

The memory is being used by the operationg system for buffers and cache. You can use the 'vmtune' or 'vmo' (dep. on OS version) command to see how much memory the system will keep available.
Default is 120 pages which is 0.5MB.
If 2GB stayed available you should be nervous.

Cheers

Henrik Morsing
Certified AIX 4.3 Systems Administration
& p690 Technical Support

 

[mlcboy01]

Henrik Morsing,

Thanks for the reply!

I'm very curious about this statement: "If 2GB stayed available you should be nervous." If you wouldn't mind, can you give me either the why-for, or suggest a reference I might look that would explain why I should be "nervous"?

I'm beginning to believe that what I'm seeing is a result of the 32bit operating systems addressable memory limit of 2GB. When I run vmtune or ipcs, it is showing me statistics from the first (0-2GB) 32bit address space. The system knows it has 8GB of physical memory, it just can't show me what's going on in the 6GB above the first 2GB.

Am I on the right track?

 

[Morsing]

I'm not sure I understand exactly what you mean. What 2GB are you talking about?
If you mean that it can only use 2GB memory for processes then it sounds like you only have 2GB of paging space and are using early paging space allocation. As far as I remember 4.3.3 had started using deferred paging space allocation though but I can't remember for sure.

I suggest you read IBMs Redbook "Performance tools and Techniques" which explains all this in detail.

Cheers

Henrik Morsing
Certified AIX 4.3 Systems Administration
& p690 Technical Support

 

[GeoffTorres]

Your memory is all there.

vmstat reports memory stats in pages which are 4kb in size.

1972498 * 4096 = 8079351808

Which is pretty darn close to 8 GB.

Geoff

 

[tomaix]

GeoffTorres and Unixtechie!...I do agree to ur point. According to the output pasted, 8G Memory is very much available for usage.

Tom.

 

[mlcboy01]

GeoffTorres, Unixtechie and tomaix,

Thanks folks!B-)