0292c54bdb
In very high throughput workloads, the inactive scan can become overwhelmed as you have many cores producing pages and a single core freeing. Since Mark's introduction of batched pagequeue operations, we can now run multiple inactive threads working on independent batches. To avoid confusing the pid and other control algorithms, I (Jeff) do this in a mpi-like fan out and collect model that is driven from the primary page daemon. It decides whether the shortfall can be overcome with a single thread and if not dispatches multiple threads and waits for their results. The heuristic is based on timing the pageout activity and averaging a pages-per-second variable which is exponentially decayed. This is visible in sysctl and may be interesting for other purposes. I (Jeff) have verified that this does indeed double our paging throughput when used with two threads. With four we tend to run into other contention problems. For now I would like to commit this infrastructure with only a single thread enabled. The number of worker threads per domain can be controlled with the 'vm.pageout_threads_per_domain' tunable. Submitted by: jeff (earlier version) Discussed with: markj Tested by: pho Sponsored by: probably Netflix (based on contemporary commits) Differential Revision: https://reviews.freebsd.org/D21629
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