Re: [PATCH] mm/hugetlb: Warn the user when issues arise on boot due to hugepages

["Liam R. Howlett" <Liam.Howlett@Oracle.com>]

* Michal Hocko <mhocko@suse.com> [170617 02:51]:
> On Fri 16-06-17 12:07:55, Andrew Morton wrote:
> > On Mon, 12 Jun 2017 21:35:17 -0400 "Liam R. Howlett" <Liam.Howlett@Oracle.com> wrote:
> > 
> > > > 
> > > > > If there's no message stating any
> > > > > configuration issue, then many admins would probably think something is
> > > > > seriously broken and it's not just a simple typo of K vs M.
> > > > > 
> > > > > Even though this doesn't catch all errors, I think it's a worth while
> > > > > change since this is currently a silent failure which results in a
> > > > > system crash.
> > > > 
> > > > Seriously, this warning just doesn't help in _most_ miscofigurations. It
> > > > just focuses on one particular which really requires to misconfigure
> > > > really badly. And there are way too many other ways to screw your system
> > > > that way, yet we do not warn about many of those. So just try to step
> > > > back and think whether this is something we actually do care about and
> > > > if yes then try to come up with a more reasonable warning which would
> > > > cover a wider range of misconfigurations.
> > > 
> > > Understood.  Again, I appreciate all the time you have taken on my
> > > patch and explaining your points.  I will look at this again as you
> > > have suggested.
> > 
> > So do we want to drop
> > mm-hugetlb-warn-the-user-when-issues-arise-on-boot-due-to-hugepages.patch?
> > 
> > I'd be inclined to keep it if Liam found it a bit useful - it does have
> > some overhead, but half the patch is in __init code...
> 
> I would rather see a more generic warning that would catch more
> misconfiguration than those ultimately broken ones. If we find out that
> such a warning is not feasible then I would not oppose to go with the
> current approach but let's try a bit harder before we go that way.
> 
> Liam, are you willing to go that way?

As I see it, and as you have pointed out, we can only be sure it's an
error if it's over 100% of the memory.  Although it's certainly worth
while looking for a way to detect an incorrect configuration that
doesn't meet this criteria, I'm not sure it's worth holding out to make
the change.  I think giving any direct message could save someone a lot
of debug time.  If it's okay, I'd like to go ahead with the change and
also look for a way to correct and notify of a broader range of
configurations that cause severe issues in regards to hugepages.

Thanks,
Liam

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