topic Re: Where fore art thou RAM...? in Operating System - Linux

Where fore art thou RAM...?

Michael Williams_6 — Fri, 03 Sep 2004 10:20:52 GMT

Hello all, I have a SLES8 system but I imagine the problem is the same no matter which Linux you're using...

I have a box which had 1Gig RAM in it when built and upgraded to 4Gig later on. Another system built in an identical manner had 4Gig from day one.

To make things easier for us, I'm going to call the server built with 1Gig Server1. I'm going to call the server built with 4Gig Server4.

Now my problem is that Server4 is running like a dog as there's only 100Meg RAM free, yet on Server1 there's 2Gig RAM free. Here's the memory output of top:

Server1:
Mem: 3622784k total, 394836k used, 3227948k free, 61776k buffers
Swap: 2097136k total, 0k used, 2097136k free, 126040k cached

Server4:
Mem: 3622784k total, 3518724k used, 104060k free, 36400k buffers
Swap: 2097136k total, 0k used, 2097136k free, 2841752k cached

Both servers are running idle and fresh from boot, there's nothing running outside your normal daemons and HP's agents. Both systems are HP DL380G4's, dual processors. Both systems were built the same and have the SP3 level, I am running HP's drivers for the hardware.

The output from /proc/meminfo is below:

Server1:
trtag1:~ # cat /proc/meminfo
total: used: free: shared: buffers: cached:
Mem: 3709730816 403984384 3305746432 0 63586304 129064960
Swap: 2147467264 0 2147467264
MemTotal: 3622784 kB
MemFree: 3228268 kB
MemShared: 0 kB
Buffers: 62096 kB
Cached: 126040 kB
SwapCached: 0 kB
Active: 155764 kB
Inactive: 53028 kB
HighTotal: 2752460 kB
HighFree: 2569340 kB
LowTotal: 870324 kB
LowFree: 658928 kB
SwapTotal: 2097136 kB
SwapFree: 2097136 kB
BigFree: 0 kB

Server4:
total: used: free: shared: buffers: cached:
Mem: 3709730816 3602726912 107003904 0 37412864 2909954048
Swap: 2147467264 0 2147467264
MemTotal: 3622784 kB
MemFree: 104496 kB
MemShared: 0 kB
Buffers: 36536 kB
Cached: 2841752 kB
SwapCached: 0 kB
Active: 747208 kB
Inactive: 2606460 kB
HighTotal: 2752460 kB
HighFree: 2992 kB
LowTotal: 870324 kB
LowFree: 101504 kB
SwapTotal: 2097136 kB
SwapFree: 2097136 kB
BigFree: 0 kB

So, has anyone got a clue where my RAM's gone on Server4 so my RAM intensive apps can use the bloody 4Gig I bought for it in the first place?!?!

Thanks in advance for your help!

Mike

Re: Where fore art thou RAM...?

Steven E. Protter — Fri, 03 Sep 2004 11:11:47 GMT

There does not appear to be anything in the report that would explain this situation.

You may need to connect some sar data to figure out what is going on. This may be appliation/use releated, though neither machine is actually using any swap.

sar -qM 1 600 # 10 minutes
sar -uM 1 600
sar -b 1 600
sar -d 1 600
sar -w 1 600
sar -v 1 600

might want to run this in the background via a script.

This is a quick port of an hp-ux script and may need some work on the command line parameters.

Looks tome like all memory is available.

SEP

Re: Where fore art thou RAM...?

Olivier Drouin — Fri, 03 Sep 2004 14:57:50 GMT

The memory seems to be available.

Like Steven said...some sar output may help.

Did the server slowed down after installing memory or you just doesnt see any difference than before ?

Re: Where fore art thou RAM...?

Chris Saunderson — Tue, 07 Sep 2004 16:34:14 GMT

It appears that most of the memory is in disk cache. The Cached: line gives it away.

Normally, this isn't a problem as it indicates that some intensive read/write has gone on on the server and that the OS has cached those blocks for quicker access.

Does this continue over time?

Re: Where fore art thou RAM...?

Michael Williams_6 — Tue, 14 Sep 2004 03:48:29 GMT

Huy guys,

You're all way off! It turns out that the amount of RAM free is MemFree + Inactive...

While not identical, it does show me where most of my RAM has gone. It turns out that Linux is pretty clever with apps and loads the image into the RAM so the next time it's run it'll load quicker. This is then "free" RAM if an application actually needs it and is swapped out accordingly...

D'oh!

Re: Where fore art thou RAM...?

Michael Williams_6 — Tue, 14 Sep 2004 03:48:53 GMT

Err, read above.