What "very low numbers" are you looking at? Are you looking at the overall
system memory in the header of top's output?
If so, then it's normal behaviour from modern operating systems. The short
answer is "what good is all this memory if it's not used?" It's easily
available to processes if needed.
When you look at the output from top or free, it's giving you most of the
information to figure out what's used and what's "free". What you need to
do is look at the buffers and cached lines. Those indicate how much memory
processes are using to cache (i.e. file buffers, input queues, etc) and
disk I/O, respectively. These are Good Things, as accessing memory is much
(by an order of magnitude or so) faster then accessing disk. A lot of the
memory that is consumed by buffers and caches is easy to free, the only
cost being that the system will slow down as it has to go to the hard
drive to retrieve data more frequently.
If you're ever curious to know how much memory is really available, try
the command 'free -mt'. It reports the current snapshot of overall memory
utilization. On my system, it reports this:
[EMAIL PROTECTED] /home/jfurtner $ free -mt
total used free shared buffers cached
Mem: 2027 1976 51 0 178 781
-/+ buffers/cache: 1016 1010
Swap: 1961 306 1654
Total: 3988 2283 1705
Which indicates that of the 2 GB of RAM, 50 MB are not in use, but about
1000 MB are available. Notice the line beginning with "-/+ buffers/cache",
subtract the buffers from used, and add the cache to free to see how much
memory would really be available if it's needed. When I ran the free
command, there was about 1050MB available if needed (about 50 MB free),
and about 900 MB used by processes.
It's not a sign that there's any "leakage", it's the kernel attempting --
and succeeding most of the time -- to increase the performance of the
machine by caching frequently/recently used data.
This is explained more in depth at
http://gentoo-wiki.com/FAQ_Linux_Memory_Management
Jamie
On Thu, April 27, 2006 12:34 pm, shane wrote:
> Hi All,
>
>
> I have an idle curiousity I'm hoping someone might indulge...
>
>
> I am one of those people who likes to check out 'top' every once in a
> while for no discernable reason. I imagine that it's somewhat like my
> impulse to periodically look in the fridge just to see what's in there.
>
> (yes ha-ha, perhaps I spend a bit too much time with a computer)
>
>
> I've noticed after a re-start, top reports very low numbers, which makes
> sense. Everything is fresh.
>
> Over time, these these numbers grow. Which, I guess is kinda expected as
> well but what I'm curious about is:
>
> Aren't programs supposed free memory after they have used it?
>
>
> Isn't the gradual accumulation of memory usage sign of a memory leak in
> one or more applications (rarely, if ever do I see 'zombies')?
>
> Thanks,
>
>
> Shane
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