It is my understanding that the memory 'in use' doesn't just include
the memory being used by all running processes combined. It also includes
memory used to store information just in case it is needed. This extra
memory can be given up to a process that needs it and has a right to use
more memory than it already uses.
In tcsh the "limit" command and in bash the "ulimit -a" command will,
for the user running it, tell if there is any limit on memory usage for
them. The user should see "unlimited"; otherwise that could account
for the problem.
If your kernel was compiled with "CONFIG_NOHIGHMEM" ("locate
Configure.help" to find documentation on this), processes will
not be able to use more than 1 GB, regardless of the limit/ulimit
setting.
On Wed, 31 Jul 2002, Urte F�rst wrote:
>
> Hi list,
>
> I just detected a rather strange memory behaviour on (at least) one of
> our redhat 7.1 machines (kernel 2.4.9-6, DELL Precision 530 2x1.7GHz).
> I wonder if anybody can point me in the right direction or give me
> some URL for further reading and understanding.
>
> The user on that machine is running a memory-expensive flow solver,
> and as the 2GB RAM weren't enough ( :-) ) we upgraded to 4GB RAM about
> two weeks ago. The first thing we noticed was, that the kernel mentioned
> only 3.7GB instaed of 4GB, but I found on the internet that this is sort
> of okay, and we could get around this by using an enterprise kernel.
> We let this as an option for the future, as the flow solver currently
> is happy with 3.7GB.
>
> In the meantime it turned out that sometimes the kernel reports a big
> chunk of the memory as 'in use' (according to top/gtop at least), but
> I am unable to figure out by which process this memory is used. When
> the user starts one of his jobs then (consuming let's say 3GB of memory)
> the machine starts swapping soon, slowing down the job significantly.
>
> My question now is: Is there a way to see which process (PID perhaps)
> is using the memory / had allocated it? It is not visible in top/gtop,
> but reported as used. Am I maybe suffering from some weakness of the
> kernel and should I try a kernel upgrade? Are there any commands by
> which I might get more information about whats going on?
>
> Thanks in advance for any hint, and kind regards,
> Urte
>
> --------
>
>
>
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Steven Yellin
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