Function vm_pageout_lowmem

freebsd/vm/vm_pageout.c:2039–2083

* Signal a free page shortage to subsystems that have registered an event * handler. Reclaim memory from UMA in the event of a severe shortage. * Return true if the free page count should be re-evaluated. */

 * Return true if the free page count should be re-evaluated.
 */
static bool
vm_pageout_lowmem(void)
{
	static int lowmem_ticks = 0;
	int last;
	bool ret;

	ret = false;

	last = atomic_load_int(&lowmem_ticks);
	while ((u_int)(ticks - last) / hz >= lowmem_period) {
		if (atomic_fcmpset_int(&lowmem_ticks, &last, ticks) == 0)
			continue;

		/*
		 * Decrease registered cache sizes.
		 */
		SDT_PROBE0(vm, , , vm__lowmem_scan);
		EVENTHANDLER_INVOKE(vm_lowmem, VM_LOW_PAGES);

		/*
		 * We do this explicitly after the caches have been
		 * drained above.
		 */
		uma_reclaim(UMA_RECLAIM_TRIM);
		ret = true;
		break;
	}

	/*
	 * Kick off an asynchronous reclaim of cached memory if one of the
	 * page daemons is failing to keep up with demand.  Use the "severe"
	 * threshold instead of "min" to ensure that we do not blow away the
	 * caches if a subset of the NUMA domains are depleted by kernel memory
	 * allocations; the domainset iterators automatically skip domains
	 * below the "min" threshold on the first pass.
	 *
	 * UMA reclaim worker has its own rate-limiting mechanism, so don't
	 * worry about kicking it too often.
	 */
	if (vm_page_count_severe())
		uma_reclaim_wakeup();

	return (ret);
}

static void
vm_pageout_worker(void *arg)