[Beowulf] confused about high values of "used" memory under "top" even without running jobs

Michael Di Domenico mdidomenico4 at gmail.com
Wed Aug 12 15:06:08 EDT 2009


My first guess is that this is likely files being cached.  We have NFS
mounts and this happens alot...  I don't regularly, but on occasion
i've sync'd the filesystems and dumped the caches with a prolog
script.  Linux doesn't seem to empty the page cache faster enough, i'm
sure theres a more eloquent way to do this

On Wed, Aug 12, 2009 at 2:55 PM, Rahul Nabar<rpnabar at gmail.com> wrote:
> I am a bit confused about the high "used" memory that top is showing on one
> of my machines? Is this "leaky" memory caused by codes that did not return
> all their memory? Can I identify who is hogging the memory? Any other ways
> to "release" this memory?
>
> I can see no user processes really (even the load average is close to
> zero), but yet 7 GB out of our total of 16GB seems to be used.
>
> ################################################
> top - 13:45:00 up 4 days, 20:07,  2 users,  load average: 0.00, 0.00, 0.00
> Tasks: 146 total,   1 running, 145 sleeping,   0 stopped,   0 zombie
> Cpu(s):  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,
> 0.0%st
> Mem:  16508824k total,  7148804k used,  9360020k free,   307040k buffers
> Swap:  8385920k total,        0k used,  8385920k free,  6380236k cached
> ###########################################################
>
> On the other hand, I recall reading somewhere before that due to the
> paging mechanism
> Linux is also supposed to start using as much memory as you give it? Just
> confused if this is something I need to worry about or not.
>
> Incidentally the way I discovered this was because users reported that their
> codes were running ~30% faster right after a machine reboot as opposed to
> after a few days running.  Do people do anything special to make sure
> that in a scheduler based environment (say PBS) the last job releases
> all its memory resources before the new one starts running?
>
> [apologize for the multi-posting ; I first posted this on a generic
> linux list but then thought that HPC guys might be more sensitive and
> concerned about such memory issues]
> --
> Rahul
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