runtime/trace: running out of memory on plan9/amd64 builder

[0intro]

Since 2019-03-06 approximately, the runtime/trace test is running out of memory on the plan9/amd64 builder.

[gopherbot]

Change https://golang.org/cl/172740 mentions this issue: dashboard: disable runtime/trace on plan9-amd64-9front

[bradfitz]

Why's it use so much memory?

How much memory does the machine have?

[0intro]

The machine has 2048 MB memory. 1822 MB are available from user space. The TestTraceStress and TestTraceStressStartStop tests are using all available memory.

[gopherbot]

Change https://golang.org/cl/172837 mentions this issue: runtime/trace: also treat plan9 as a low memory system

[0intro]

I've updated the pkan9/amd64 builder and the runtime/trace tests seem to pass now.