Maximum memory size/preformance

[Peter Teuben]

Hi Knox
 ah these problems are dear to my heart :-)    Setting the memory to
unlimited is the correct approach (it should be the default on ubuntu), so
I'm surprised to hear it's only using 670MB.  If so, it will  be trrashing
and perhaps using the swap (but there is enough memory....).   When you use
top (or install htop,it sometimes is more helpful debugging these types of
problems),  look at how big VIRT and RES are.   Do you see the task
"swapd0" appear. I hope not.

In worst case, is this a problem that can be easily run by me. I have a
machine here that has 512GB memory

- peter


On Fri, Dec 17, 2021 at 2:04 PM Knox Long <long at stsci.edu> wrote:

> I am having a problem getting a program that I have which requires a large
> amount of memory to run at the speed I think it should a recently installed
> version of ubuntu.   The same program compiled in exactly the same way
> under Cygwin runs more than 5x faster on the same machine (which has 128 GB
> of ram).  This program requires a lot of memory due to the fact that it has
> a set of very large structures (that describe the physical conditions at
> different points in the wind of quasar).  The result is the program
> requires several GB of memory.
>
>
>
> I suspect the reason that the program runs more slowly using Ubuntu is
> that the amount of physical memory being used is too small.  Even though I
> have succeeded in using ulimit to set the max locked memory to unlimited,
> it does not change the fact that top says only 670 MB of resident is being
> used, while the virtual memory is more than a GB.  (Unfortunately, I cannot
> check in Cygwin that this is the problem, because on Cygwin the top command
> produces quite different outputs.
>
>
>
> If anyone has any thoughts about this I would appreciate it.  (Note that I
> am not an expert in linux or especially ubuntu).
>
>
>
> Thanks
>
> Knox
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