Re: [PATCH 0/4] Convert khugepaged to a task_work function

[Rik van Riel]

On 10/28/2014 08:58 AM, Rik van Riel wrote:
> On 10/28/2014 08:12 AM, Andi Kleen wrote:
> > Alex Thorlton <athorlton@xxxxxxx> writes:
> >
> > > Last week, while discussing possible fixes for some unexpected/unwanted behavior
> > > from khugepaged (see: https://lkml.org/lkml/2014/10/8/515) several people
> > > mentioned possibly changing changing khugepaged to work as a task_work function
> > > instead of a kernel thread.  This will give us finer grained control over the
> > > page collapse scans, eliminate some unnecessary scans since tasks that are
> > > relatively inactive will not be scanned often, and eliminate the unwanted
> > > behavior described in the email thread I mentioned.
> >
> > With your change, what would happen in a single threaded case?
> >
> > Previously one core would scan and another would run the workload.
> > With your change both scanning and running would be on the same
> > core.
> >
> > Would seem like a step backwards to me.
>
> It's not just scanning, either.
>
> Memory compaction can spend a lot of time waiting on
> locks. Not consuming CPU or anything, but just waiting.
>
> I am not convinced that moving all that waiting to task
> context is a good idea.

It may be worth investigating how the hugepage code calls
the memory allocation & compaction code.

Doing only async compaction from task_work context should
probably be ok.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/