Re: [PATCH 1/3] Reintroduce zone_reclaim_interval for when zone_reclaim() scans and fails to avoid CPU spinning at 100% on NUMA

[KOSAKI Motohiro]

> > > Here it is just recording the jiffies value. The real smarts with the counter
> > > use time_before() which I assumed could handle jiffie wrap-arounds. Even
> > > if it doesn't, the consequence is that one scan will occur that could have
> > > been avoided around the time of the jiffie wraparound. The value will then
> > > be reset and it will be fine.
> > 
> > time_before() assume two argument are enough nearly time.
> > if we use 32bit cpu and HZ=1000, about jiffies wraparound about one month.
> > 
> > Then, 
> > 
> > 1. zone reclaim failure occur
> > 2. system works fine for one month
> > 3. jiffies wrap and time_before() makes mis-calculation.
> > 
> 
> And the scan occurs uselessly and zone_reclaim_failure gets set again.
> I believe the one useless scan is not significant enough to warrent dealing
> with jiffie wraparound.

Thank you for kindful explanation.
I fully agreed.



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