On Wed, 14 Apr 2021 14:04:33 +0000 Ray Dillinger <b...@sonic.net> wrote:
> > Warning, a coredump from this system would be immense. Or, well anyway > pretty darn large. The machine has over 64G of RAM memory installed and > openuniverse seems to expand to fill available space. I could make a VM > with artificially small memory to produce a more manageable coredump, > but I wonder whether a VM environment would tickle the spot that > provokes this bug. Testing in a VM with a more reasonable 6GB apparently does not provoke the crash. It doesn't fix the interface issues, but it doesn't outright crash. But, in light of that fact, the clues seen so far point in one direction, and if I'm right about it the backtrace probably wouldn't even be relevant to finding the problem. Consider the facts: I have a system with an unusual amount of memory. I see Openuniverse expand to fill available memory and then crash. The crash happens at an instruction to allocate memory. A virtual machine with a less-unusual amount of memory doesn't provoke this crash. Admittedly not very much to go on but what do these clues add up to? I have not even looked at the source code of openuniverse, but this is pretty clearly a memory management bug, and I have a fairly solid theory/guess as to what kind. Managing memory in big chunks can provoke flawed applications to fail in at least three ways they don't fail when managing memory in smaller chunks: First, by extending the time between deallocations and allocations (giving other applications time to allocate and spoil memory availability, provoking a crash on the next allocation). Second, by provoking the allocation of proportional size buffers while deallocating on criteria not sufficient to ensure that such a large buffer remains available, again provoking a crash on the next allocation. Third, by some static structure that keeps track of pointers to allocated memory having a finite limit that is exceeded - resulting in a buffer with an overwritten or unrecorded pointer, provoking a memory leak. Although this theory may be incorrect, these are at the very least the first "obvious" places to look. Bear
