Stack Size Estimation

Question

In multi-threaded embedded software (written in C or C++), a thread must be given enough stack space in order to allow it to complete its operations without overflowing. Co

Answer 1

We tried to solve this problem on an embedded system at my work. It got crazy, there is just too much code (both our own and 3rd party frameworks) to get any reliable answer. Luckily, our device was Linux based so we fell back to the standard behavior of giving every thread 2mb and letting the virtual memory manager optimize the use.

Our one issue with this solution was one of the 3rd party tools performed an mlock on its entire memory space (ideally to improve performance). This caused all 2mb of stack for each thread of its threads (75-150 of them) to be paged in. We lost half of our memory space to until we figured it out and commented out the offending line.

Sidenote: Linux's virtual memory manager(vmm) allocates RAM in 4k chunks. When a new thread asks for 2MB of address space for its stack, the vmm assigns bogus memory pages to all but the top most page. When the stack grows into bogus page the kernel detects a page fault and swaps the bogus page with a real one, (which consumes another 4k of actual RAM). This way a thread's stack can grow to any size it needs (as long as it's less than 2mb) and the vmm will ensure only a minimal amount of memory is used.