Debugging out-of-memory crashes using Fil

Typically when your program runs out of memory, it will crash, or get killed mysteriously by the operating system, or other unfortunate side-effects.

To help you debug these problems, Fil will heuristically try to catch out-of-memory conditions, and dump a report if thinks your program is out of memory. It will then exit with exit code 53.

$ fil-profile run 
=fil-profile= Wrote memory usage flamegraph to fil-result/2020-06-15T12:37:13.033/out-of-memory.svg

Fil uses three heuristics to determine if the process is close to running out of memory:

  • A failed allocation, indicating insufficient memory is available.
  • The operating system or memory-limited cgroup (e.g. a Docker container) only has 100MB of RAM available.
  • The process swap is larger than available memory, indicating heavy swapping by the process. In general you want to avoid swapping, and e.g. explicitly use mmap() if you expect to be using disk as a backfill for memory.

For a more detailed example of out-of-memory detection with Fil, see this article on debugging out-of-memory crashes.

Disabling the out-of-memory detection

Sometimes the out-of-memory detection heuristic will kick in too soon, shutting down the program even though in practice it could finish running. You can disable the heuristic by doing:

fil-profile --disable-oom-detection run