This pulls in the improvements introduced in:
- https://github.com/raulk/go-watchdog/releases/tag/v1.0.0
- https://github.com/raulk/go-watchdog/releases/tag/v1.0.1
Lotus tries to initialize the watchdog in the following order of precedence:
1. If a max heap limit has been provided, initialize a heap-driven watchdog.
2. Else, try to initialize a cgroup-driven watchdog.
3. Else, try to initialize a system-driven watchdog.
4. Else, log a warning that the system is flying solo, and return.
This PR also enabled automatic heap profile capture when memory usage
surpasses 90% of the limit. Profiles are written to <LOTUS_HOME>/heapprof.
A single heap profile is captured per episode, with a max of 10 episodes
captured during the lifetime of the process. Episode = instance of usage
climbing above the 90% threshold.
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