What are the good implementation practices to minimize RAM consumption

Question

I run a C code on an arm based Linux device that has a very small RAM space (16MB). My code is often killed (SIGKILL) by the kernel with 'out of memory' message. I run the program with Valgrind, and it does not look like there is a memory leak. I run the code with gdb as well but could not identify any mistake on the code. I will try to optimize my code going it through some many times.

In general, what would be the good implementation practices on a code to minimize the memory usage?

• one might be to use functions as much as possible(?), but I guess gcc already optimizes the code to decrease the source usage.
• to avoid dynamic memory allocations
• what else?

Answer 1

Be careful about scope of objects. Make sure you are handling the memory deallocation after an object is no longer needed. I'm not sure I understand your use functions as much as possible(?). Functions require overhead, every call causes a little bit of extra memory to be taken up because it has to store a few pointers and a little bit of information about the method on the call stack. So, while that may help keep your source code clean - it won't lower your memory usage (it'll probably increase it). One way to get the best of both worlds in C is to use inline functions - which suggests to the compiler that it should not create an actual function, but rather just insert that block of code wherever it is used. Keep in mind that efficient code usually has a more machine level look to it (meaning repetition, pointers, and often developer-managed array indices) rather than taking advantage of broad purpose, function abundant objects. But, thank goodness for smart compilers so you don't have to know every optimization. However, in a lower level language like c, since it gives you so much ability to manipulate everything, you need to be careful that you don't make costly mistakes.

Answer 2

If you have this kind of problem on Linux you can disable overcommit memory. It will make sure that all the memory allocated has physical memory. The kernel will be less likely to kill your program. Then be sure to test the result of all mallocs because they will fail at some point when you don't have memory anymore. You can find more information here : http://www.etalabs.net/overcommit.html

You can also disable some programs on your embedded system to free memory. May be you don't use cron or don't need six TTY at startup.