/*

			nr_writeback++;

			 * memcg doesn't have any dirty pages throttling so we

			unlock_page(page);

			 * could easily OOM just because too many pages are in

			goto keep;

			 * writeback and there is nothing else to reclaim.

			 *

			 * Check __GFP_IO, certainly because a loop driver

			 * thread might enter reclaim, and deadlock if it waits

			 * on a page for which it is needed to do the write

			 * (loop masks off __GFP_IO|__GFP_FS for this reason);

			 * but more thought would probably show more reasons.

			 *

			 * Don't require __GFP_FS, since we're not going into

			 * the FS, just waiting on its writeback completion.

			 * Worryingly, ext4 gfs2 and xfs allocate pages with

			 * grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so

			 * testing may_enter_fs here is liable to OOM on them.

			 */

			if (global_reclaim(sc) ||

			    !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) {

				/*

				 * This is slightly racy - end_page_writeback()

				 * might have just cleared PageReclaim, then

				 * setting PageReclaim here end up interpreted

				 * as PageReadahead - but that does not matter

				 * enough to care.  What we do want is for this

				 * page to have PageReclaim set next time memcg

				 * reclaim reaches the tests above, so it will

				 * then wait_on_page_writeback() to avoid OOM;

				 * and it's also appropriate in global reclaim.

				 */

				SetPageReclaim(page);

				nr_writeback++;

				goto keep_locked;

			}

			wait_on_page_writeback(page);