Recursion takes up space on stack which takes up space in caches which
means less room for useful data.
In addition to that, a limit on iteration count can be larger than the
limit on recursion, because we're not limited by stack size here.
Also, recursion makes flame-graphs really hard to analyze because
keep_doing() frames appear at different levels of nesting in the
profile leading to many short "towers" instead of one big tower.
This change reuses the same counter for limiting iterations as is used
to limit the number of tasks executed by the reactor before polling.
There was a run-time parameter added for controlling task quota.
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