Re: Sleeping BUG in khugepaged for i586

[David Rientjes]

On Mon, 12 Jun 2017, Michal Hocko wrote:

> > These are not soft lockups, these are need_resched warnings.  We monitor 
> > how long need_resched has been set and when a thread takes an excessive 
> > amount of time to reschedule after it has been set.  A loop of 512 pages 
> > with ptl contention and doing {clear,copy}_user_highpage() shows that 
> > need_resched can sit without scheduling for an excessive amount of time.
> 
> How much is excessive here?

We monitor anything that holds the cpu for more than 1/20th of a second, 
but this specific occurrence has been observed for ~1/8th.  The majority 
of mm/ is quite good in this regard.