topic Re: Out of memory in Operating System - Linux

Out of memory

ossupport55 — Wed, 05 Aug 2009 11:34:28 GMT

Dear all,

I've got 2 issues:

1. a RHEL Update 4 node was hanging with the error " Out Of Memory: Killed Process 21344 ( oracle ). It's a X64. What could be the issue?

2. Well, what is the most accurate way to get the free memory of the server. I was told to check:

free -m
total used free shared buffers cached
Mem: 16010 15990 20 0 69 10615
-/+ buffers/cache: 5304 10705
Swap: 4031 2314 1717

according to the above command, the system has 10705 free memory.

- top says 21180k free

- vmstat says 21300 free.

- meminfo says MemFree: 42556 kB

But there is a minute time diff as i was copying and pasting across. Please enlighten me.

cheers

Re: Out of memory

Fayez — Wed, 05 Aug 2009 12:40:57 GMT

Hi,

How much memory there in your server???
Check how much of memory the oracle are use.
from the output of all commands, there is not enough memory to run normal system ( almost 42MB free), so I think you have bad memory utilization or you really need more memory for your system.

Re: Out of memory

Ivan Ferreira — Wed, 05 Aug 2009 12:45:10 GMT

The real used memory for applications it's what you see on +/- buffers/cache. This has been discussed a lot in this forum.

It's impossible to determine the cause of the problem with the information provided. I suggest you to install "collect for linux" collectl and capture performance information.

Re: Out of memory

Court Campbell — Wed, 05 Aug 2009 12:56:00 GMT

the oom killer kicked in. Please provide this output:

sysctl vm.overcommit_memory

Re: Out of memory

ossupport55 — Thu, 06 Aug 2009 03:53:56 GMT

Thanks to all,

Court Campbell, yes out of memory setting is at it's default.
vm.overcommit_memory = 0
should i make it 2. i think if it's to be done it should be done on a reactive basis rather than proactive. We have over 300 servers.
Ivan, can you please provide me some reference about memory usage and free memory allocation. According to my post, vmstat,top and the meminfo file is useless is it ?
Fayez, MemTotal: 16394912 kB is the one which is reported in /proc/meminfo, well now i have doubts whether these are really acceptable readings.

Finally, gurus please provide me some reference on how to get to know the actual memory utilisation physical/virtual.

cheers!

Re: Out of memory

Mike Stroyan — Thu, 06 Aug 2009 16:40:34 GMT

The rule about looking at "free" output and adding the free and cache
values is generally correct. But it oversimplifies. Much of the
cache memory is easily released for reuse. But shared memory segments
can appear as "cached" memory although that cannot actually be freed.
If you look at the output of "ipcs -u" you can see the size of shared
memory segments. The values are reported in terms of pages rather
than 1K or 1M. The page size is almost always 4K, but varies on some
architectures. You can check that with the "getconf PAGESIZE" command.
Shared memory can be pushed from RAM to swap if swap space is available.
Doing that will be slower than releasing clean cache memory, since the
data will need to be written out to disk. If swap space runs out then
a system can start doing out of memory kills even though there is still
a lot of "cached" memory remaining.