Hi, were are noticing that one of our servers sitting in a DR site is doing nothing but has a memory usage of 95% sitting idle. Here is some top output:

op - 14:44:33 up 252 days, 6:00, 3 users, load average: 0.00, 0.00, 0.00
Tasks: 75 total, 1 running, 74 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.1% us, 0.0% sy, 0.0% ni, 99.9% id, 0.0% wa, 0.0% hi, 0.0% si
Mem: 2074920k total, 1951568k used, 123352k free, 395588k buffers
Swap: 4192956k total, 0k used, 4192956k free, 1365392k cached

PID USER PR NI %CPU TIME+ %MEM VIRT RES SHR S COMMAND
14970 root 16 0 0 0:00.55 0.0 3316 1000 780 R top
1 root 16 0 0 0:00.96 0.0 2060 508 432 S init
2 root RT 0 0 0:03.30 0.0 0 0 0 S migration/0
3 root 34 19 0 0:00.19 0.0 0 0 0 S ksoftirqd/0
4 root RT 0 0 0:02.72 0.0 0 0 0 S migration/1
5 root 34 19 0 0:00.13 0.0 0 0 0 S ksoftirqd/1
6 root RT 0 0 0:02.23 0.0 0 0 0 S migration/2
7 root 34 19 0 0:00.09 0.0 0 0 0 S ksoftirqd/2
8 root RT 0 0 0:02.44 0.0 0 0 0 S migration/3
9 root 34 19 0 0:00.10 0.0 0 0 0 S ksoftirqd/3

Could this be because the box has been up for so long? This is a Redhat system that basically serves a web server. We only use it one or twice a year to perform DR test. What could be causing such high memory usage?


Thanks

When a program releases memory Linux just doesn't throw the old memory contents away. It keeps the memory contents available in case anyone wants to use the memory again. So after Linx has been running a while memory usage always approaches 100% even though some of the supposedly used memory is simply free memory that nobody is using. Once memory is fully used then the kernel meets new memory allocation requests by freeing memory that has not been actually used for a while and allocating it to the new request.

So the answer is that all Linux systems run with high memory usage whether the memory is currently being actively used or not. The only exception is immediately after boot when you will find a lot of free memory available because it has not been used and released yet.

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Steve Stites

jailbait,


Thanks for the insanely fast reply. Is there any tool we can use to free up this unused memory to the state that it was in before the process occupied that chunk of memory rather than just rebooting? Some what like flushing the memory space?

Linux will release the memory as needed. It had me baffled also when I started analyzing memory stats, but it works just fine as is.
I don't know of a tool to release it so that it will show as unused.

There is no need - as explained, the memory is already "free". For a better idea of what is actually in use by "programs", use "free -m".
Look at the "used" number in the "-/+ buffers/cache" line.
This gets asked all the time - search for other threads.

Ok thanks for the help guys once again another problem solved by the gurus.