mm/mglru: don't sync disk for each aging cycle

wakeup_flusher_threads() was added under the assumption that if a system
runs out of clean cold pages, it might want to write back dirty pages more
aggressively so that they can become clean and be dropped.

However, doing so can breach the rate limit a system wants to impose on
writeback, resulting in early SSD wearout.

Link: https://lkml.kernel.org/r/YzSiWq9UEER5LKup@google.com
Fixes: bd74fdae ("mm: multi-gen LRU: support page table walks")
Signed-off-by: NYu Zhao <yuzhao@google.com>
Reported-by: NAxel Rasmussen <axelrasmussen@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>

mm/vmscan.c

@@ -4413,8 +4413,6 @@ static bool try_to_inc_max_seq(struct lruvec *lruvec, unsigned long max_seq,
 	if (wq_has_sleeper(&lruvec->mm_state.wait))
 		wake_up_all(&lruvec->mm_state.wait);
 
-	wakeup_flusher_threads(WB_REASON_VMSCAN);
-
 	return true;
 }