For the very same code memory is not released after a "clear" on Ubuntu but is on Windows

Hello, I use matlab R2021b under both windows and ubuntu. There are already topics about this, but this time I noticed that my code was running correctly under windows while it don't work under ubuntu, (ie ubuntu kills matlab without any error message, but when I checked with the "top" command, I saw that the 32 GB of ram was all used) I put clear everywhere in my code, but they are only working under windows and not truly effective on ubuntu. The Ram is saturated under ubuntu (32GB RAM) while it is not under windows (16GB RAM) even though I have half as much RAM on this PC.

Do you have a solution to this problem of memory management of matlab and ubuntu?

[Jan]

clear is rarely useful in Matlab. Matlab is killed, but still visible in top?

[Dylan]

When matlab is killed all the RAM is available and matlab is no more visible in top. But the problem is when I clear a variable un matlab, I see in top that the memory allocated for matlab is not released, the variable is removed from the workspace but the memory still occupied for ubuntu.

[Jan]

@Dylan: This is a correct observation. Clearing a variable marks the memory as usable on demand, but it is not released. This is more efficient that requesting new memory on demand. As said before, clear is rarely useful in Matlab. An exception is the need to create multiple variable one after the other, which would exhaust the RAM. Then a clearing allows to re-use the memory. But if a function is left, the variables are cleared automatically already and overwriting of existing variables doe s not profit from clearing also.

[Dylan]

Thank you for the explanation ! What do you propose in order to be able to load a large amount of data, process it, and release memory step by step during the processing when a variable is no more usefull ?

Answer 1

[Steven Lord]

I suspect that the Out of Memory Killer is what killed MATLAB on your Ubuntu machine. See this webpage for more information and instructions on how to check if my suspicion is correct. I don't believe Windows has an equivalent to the OOM Killer and that's why your code continued to run on Windows.

The Ram is saturated under ubuntu (32GB RAM) while it is not under windows (16GB RAM) even though I have half as much RAM on this PC.

How specifically did you determine this on the two systems?

[Dylan]

Thanks you very much for your answer I will check that !

I run the code on the machine and watch during its execution:

for windows: the the task manager --> performance --> memory and see that the memory is freed always a clear is used.

for ubuntu: top command shows me that the memory used for matlab is always increasing until it reachs a maximum, and maybe the OOM killer operate at this moment.

[Bruno Luong]

Some graphical outputs can be source of memory leak and it is out of reach by clear command.

[Dylan]

yes, but there is no graphical output in my case. It is just a big cell of structures and I perform some mathematical operations that's all.