Merge "mm: vmscan: do not scale writeback pages when deciding whether to set ZONE_WRITEBACK"

	 * as there is no guarantee the dirtying process is throttled in the

	 * same way balance_dirty_pages() manages.

	 *

	 * This scales the number of dirty pages that must be under writeback

	 * before a zone gets flagged ZONE_WRITEBACK. It is a simple backoff

	 * function that has the most effect in the range DEF_PRIORITY to

	 * DEF_PRIORITY-2 which is the priority reclaim is considered to be

	 * in trouble and reclaim is considered to be in trouble.

	 *

	 * DEF_PRIORITY   100% isolated pages must be PageWriteback to throttle

	 * DEF_PRIORITY-1  50% must be PageWriteback

	 * DEF_PRIORITY-2  25% must be PageWriteback, kswapd in trouble

	 * ...

	 * DEF_PRIORITY-6 For SWAP_CLUSTER_MAX isolated pages, throttle if any

	 *                     isolated page is PageWriteback

	 *

	 * Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number

	 * of pages under pages flagged for immediate reclaim and stall if any

	 * are encountered in the nr_immediate check below.

	 */

	if (nr_writeback && nr_writeback >=

			(nr_taken >> (DEF_PRIORITY - sc->priority)))

	if (nr_writeback && nr_writeback == nr_taken)

		zone_set_flag(zone, ZONE_WRITEBACK);

	/*