Function vm_pageout_inactive_dispatch

freebsd/vm/vm_pageout.c:1654–1703

* Dispatch a number of inactive threads according to load and collect the * results to present a coherent view of paging activity on this domain. */

 * results to present a coherent view of paging activity on this domain.
 */
static int
vm_pageout_inactive_dispatch(struct vm_domain *vmd, int shortage)
{
	u_int freed, pps, slop, threads, us;

	vmd->vmd_inactive_shortage = shortage;
	slop = 0;

	/*
	 * If we have more work than we can do in a quarter of our interval, we
	 * fire off multiple threads to process it.
	 */
	threads = vmd->vmd_inactive_threads;
	if (threads > 1 && vmd->vmd_inactive_pps != 0 &&
	    shortage > vmd->vmd_inactive_pps / VM_INACT_SCAN_RATE / 4) {
		vmd->vmd_inactive_shortage /= threads;
		slop = shortage % threads;
		vm_domain_pageout_lock(vmd);
		blockcount_acquire(&vmd->vmd_inactive_starting, threads - 1);
		blockcount_acquire(&vmd->vmd_inactive_running, threads - 1);
		wakeup(&vmd->vmd_inactive_shortage);
		vm_domain_pageout_unlock(vmd);
	}

	/* Run the local thread scan. */
	vm_pageout_scan_inactive(vmd, vmd->vmd_inactive_shortage + slop);

	/*
	 * Block until helper threads report results and then accumulate
	 * totals.
	 */
	blockcount_wait(&vmd->vmd_inactive_running, NULL, "vmpoid", PVM);
	freed = atomic_readandclear_int(&vmd->vmd_inactive_freed);
	VM_CNT_ADD(v_dfree, freed);

	/*
	 * Calculate the per-thread paging rate with an exponential decay of
	 * prior results.  Careful to avoid integer rounding errors with large
	 * us values.
	 */
	us = max(atomic_readandclear_int(&vmd->vmd_inactive_us), 1);
	if (us > 1000000)
		/* Keep rounding to tenths */
		pps = (freed * 10) / ((us * 10) / 1000000);
	else
		pps = (1000000 / us) * freed;
	vmd->vmd_inactive_pps = (vmd->vmd_inactive_pps / 2) + (pps / 2);

	return (shortage - freed);
}

/*
 * Attempt to reclaim the requested number of pages from the inactive queue.