Who is leaking memory in my Linux Jessie/KDE4 installation?

[Omer Zak]

Hello Shimi and Oleg,
Thanks for helping me clarify what I mean by "memory leak" in this
context.

I routinely monitor memory usage by means of gnome-system-monitor, and
it appears to display memory consumption by watching the
used -/+ buffers/cache number.

As the time since last reboot lengthens, the above memory usage number
creeps upwards.  I cannot get it back to the value it had shortly after
reboot by closing all heavy applications.  This is why I am referring to
it as "memory leak".

This kind of memory usage concerns me, because when more than 90% of
memory is being used, the system slows down.  It is not because swap
memory is used (swap usage remains 0% at all times) but apparently
because there is not enough free memory to buffer/cache the entire
working set of frequently-used files.

When the system slows down, I reboot it and few more days pass before
memory usage (-/+ buffers/cache) again nears 90%.

So I am interested in finding who is hogging memory at expense of the
buffer/cache memory.  Furthermore, I'd like to find out who is hogging
more and more memory as time passes on.

--- Omer



On Fri, 2014-08-29 at 20:14 +0300, Oleg Goldshmidt wrote:
> Omer Zak <w1 at zak.co.il> writes:
> 
> > I have a 8GB PC which runs Linux Debian Jessie with KDE 4.4.
> > My problem is to find out who is occupying almost 4GB memory some time
> > after rebooting, even when nothing heavy is running.
> 
> What is your question? The subject mentions "leaking", while the body of
> your post seems to indicate (I am guessing a bit) that what bothers you
> is that most of your memory is reported as "used" rather than as
> "free" or "available". 
> 
> If an application really leaks memory you should normally be able to
> observe it by running top or similar and seeing, say, RES increasing
> with time.
> 
> If your problem is "too much memory is reported as used" then you should
> know that most of memory is "used" by something. This does not mean it
> is not available. The classic case is memory that is - or was - used for
> buffers or cache.
> 
> > However, even when they are closed, a lot memory is still reported to
> > be in use.
> 
> Operating systems do not free memory until someone requests it - again,
> your buffers and cached stuff are primary examples, as explained
> above. If you look at the "Mem" line of your top(1) or free(1) it will
> *always* report most of your memory as "used". Here is my free(1) output
> on an old laptop with 4G of RAM:
> 
> $ free
>              total       used       free     shared    buffers     cached
> Mem:       3941664    3522680     418984          0     218636    2208160
> -/+ buffers/cache:    1095884    2845780
> Swap:      6029308     113872    5915436
> 
> How much memory is used? About 1GB, actually, with ~3GB available. See
> the 2nd line, which takes into account that whatever is listed as
> buffers+cache are available for applications if/when they request it.
> 
> Check your free(1), if you see anything suspicious, post it.
>  
> > My question is: besides top, what tools can be used to find who is using
> > all this memory?
> 
> Find out the PIDs of the processes you suspect (make top sort by RES by
> typing Fq in top?) and do
> 
> egrep "^Vm" /proc/<pid>/status
> 
> for each - it will give you a lot of detailed info. If you suspect a
> leak repeat a few times while the suspect process is running (and doing
> something).
> 
> Relevant details have been discussed here before (guilty). Check
> 
> http://www.mail-archive.com/linux-il@cs.huji.ac.il/msg31797.html
> http://mailman.cs.huji.ac.il/pipermail/linux-il/2011-December/008322.html
> 
> - you will either find that useful or it will help you sleep (well).
> 
> > The next question, of course, is how to get rid of those memory hogs
> > without destabilizing the system.
> 
> First, find out if there is a problem, and what the problem is.
> 

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