I tested by running several buildworlds while I counted calls to the functions and cycles consumed by each. However, the test does not invoke vm_pageout_cluster, so I have nothing to report there.
The results for collect_flush builds
```
Original: calls cycles/call
collect_flush: 27932 211996.08194901905
collect_flush: 27929 251115.502560063
collect_flush: 27928 241602.81674305355
collect_flush: 27928 251525.5270338012
Modified:
collect_flush: 27930 245027.55209452202
collect_flush: 27929 218708.71560027212
collect_flush: 27935 216557.6463576159
collect_flush: 27928 245812.133772558
```
I ran the same performance tests again, this time with 8 buildworlds each. The results seem somewhat stronger this time:
```
Original calls cycles/call
collect_flush: 27930 238677.43537414967
collect_flush: 27930 250475.11654135337
collect_flush: 27932 259726.17070027208
collect_flush: 27932 297773.24473721895
collect_flush: 27928 192785.1349183615
collect_flush: 27928 312408.6640289315
collect_flush: 27929 282836.25210354826
collect_flush: 27928 246372.77889573187
Modified
collect_flush: 27928 172326.66535376682
collect_flush: 27928 248758.4892938986
collect_flush: 27934 166150.61530751057
collect_flush: 27929 240582.02026567367
collect_flush: 27931 211924.16254341055
collect_flush: 27930 237029.7113139993
collect_flush: 27928 217306.89551704383
collect_flush: 27930 182143.34962406015
```