WIP: add jobtap plugin for preemption #6580
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Problem: RFC 14 specifies that a job can set the preemptible-after system attribute in their jobspec to signal that the job can be preempted, but flux-core and flux-sched currently ignore this. The scheduler is the proper place to handle preemption, but in the mean time, provide a jobtap plugin that can do a sloppy job of it without knowledge of the schedule.
Problem: there are no tests for the killbot preemption plugin. Add a sharness test.
Codecov ReportAttention: Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## master #6580 +/- ##
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+ Coverage 79.47% 79.49% +0.01%
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Files 531 532 +1
Lines 88312 88607 +295
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+ Hits 70184 70434 +250
- Misses 18128 18173 +45
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This is a first cut at a jobtap plugin that dispatches preemptible jobs when there is job pressure from non-preemptible jobs, as discussed in #6524. It handles
preemptible-after > 0and doesn't preempt jobs in queues that don't have pressure.That's about the extent of its smarts!
There's a comment at the top of the plugin that explains how it works, but the quick summary is that there are currently two "handlers" that are invoked periodically while there are potential victims and job pressure. If the
overkillhandler is selected, it kills all eligible victims in one go. If theonekillhandler is selected, it kills one random victim, then waits a while and tries again if there is still pressure.This is a WIP because probably we'll need another handler that's smart about node counts, and because testing doesn't cover queues yet. I was reaching a quitting point for the weekend and wanted to get this up.