From: Jiang Biao <redacted>
Subject: mm/vmstat.c: erase latency in vmstat_shepherd

Many 100us+ latencies have been deteceted in vmstat_shepherd() on CPX
platform which has 208 logic cpus.  And vmstat_shepherd is queued every
second, which could make the case worse.

Add schedule point in vmstat_shepherd() to erase the latency.

Link: https://lkml.kernel.org/r/20210111035526.1511-1-benbjiang@tencent.com
Signed-off-by: Jiang Biao <redacted>
Reported-by: Bin Lai <redacted>
Cc: Christoph Lameter <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/vmstat.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/mm/vmstat.c~mm-vmstatc-erase-latency-in-vmstat_shepherd
+++ a/mm/vmstat.c

@@ -1980,6 +1980,8 @@ static void vmstat_shepherd(struct work_
 
 		if (!delayed_work_pending(dw) && need_update(cpu))
 			queue_delayed_work_on(cpu, mm_percpu_wq, dw, 0);
+
+		cond_resched();
 	}
 	put_online_cpus();
 

_