mm/cgroup/reclaim: fix dirty pages throttling on cgroup v1

balance_dirty_pages doesn't do the required dirty throttling on cgroupv1. 
See commit 9badce0 ("cgroup, writeback: don't enable cgroup writeback
on traditional hierarchies").  Instead, the kernel depends on writeback
throttling in shrink_folio_list to achieve the same goal.  With large
memory systems, the flusher may not be able to writeback quickly enough
such that we will start finding pages in the shrink_folio_list already in
writeback.  Hence for cgroupv1 let's do a reclaim throttle after waking up
the flusher.

The below test which used to fail on a 256GB system completes till the the
file system is full with this change.

root@lp2:/sys/fs/cgroup/memory# mkdir test
root@lp2:/sys/fs/cgroup/memory# cd test/
root@lp2:/sys/fs/cgroup/memory/test# echo 120M > memory.limit_in_bytes
root@lp2:/sys/fs/cgroup/memory/test# echo $$ > tasks
root@lp2:/sys/fs/cgroup/memory/test# dd if=/dev/zero of=/home/kvaneesh/test bs=1M
Killed

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Aneesh Kumar K.V <[email protected]>
Suggested-by: Johannes Weiner <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: zefan li <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: kvaneesh

mm/vmscan.c

@@ -2514,8 +2514,20 @@ static unsigned long shrink_inactive_list(unsigned long nr_to_scan,
 	 * the flushers simply cannot keep up with the allocation
 	 * rate. Nudge the flusher threads in case they are asleep.
 	 */
-	if (stat.nr_unqueued_dirty == nr_taken)
+	if (stat.nr_unqueued_dirty == nr_taken) {
 		wakeup_flusher_threads(WB_REASON_VMSCAN);
+		/*
+		 * For cgroupv1 dirty throttling is achieved by waking up
+		 * the kernel flusher here and later waiting on folios
+		 * which are in writeback to finish (see shrink_folio_list()).
+		 *
+		 * Flusher may not be able to issue writeback quickly
+		 * enough for cgroupv1 writeback throttling to work
+		 * on a large system.
+		 */
+		if (!writeback_throttling_sane(sc))
+			reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK);
+	}
 
 	sc->nr.dirty += stat.nr_dirty;
 	sc->nr.congested += stat.nr_congested;