Avi Kivity ca0c006b37 logalloc: background reclaim ...

Set up a coroutine in a new scheduling group to ensure there is
a "cushion" of free memory. It reclaims in preemptible mode in
order to reduce reactor stalls (constrast with synchronous reclaim
that cannot preempt until it achieved its goal).

The free memory target is arbitrarily set at 60MB. The reclaimer's
shares are proportional to the distance from the free memory target;
so a workload that allocates memory rapidly will have the background
reclaimer working harder.

I rolled my own condition variable here, mostly as an experiment.
seastar::condition_variable requires several allocations, while
the one here requires none. We should formalize it after we gain
more experience with it.

2021-02-14 19:09:29 +02:00

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