Set --solver-max-memory to 80/90% of the system's memory by default

[montyly]

Is your feature request related to a problem? Please describe.
Right now, if --solver-max-memory is not set, halmos might end up using all the system's memory and freezing the system.

Most of normal users don't want to have to set --solver-max-memory on every run.

Describe the solution you'd like
By default,--solver-max-memory could be auto set to 80-90% of the system memory.

[0xkarmacoma]

there are a couple complications with this:

• there can be multiple solver instances running at the same time
• tools like jsi spawn subprocesses that can each run into memory limits
• not sure there is a great cross-platform way to do this

maybe the most reliable thing we can do is that halmos can itself periodically monitor the memory usage of the process hierarchy in its process pool and kill things that go over the limit

[montyly]

Ah I see.

Does it mean that --solver-max-memory doesn't really work if the solver runs through multiple instances?

[0xkarmacoma]

if we treat it as a per-solver instance limit (which is the case atm), then it doesn't really work. We could change the meaning to say "I want all the running solvers to collectively use up to --solver-max-memory"