Re: hugepage related lockdep trace.

From: Michal Hocko
Date: Tue Jul 30 2013 - 10:30:09 EST

On Mon 29-07-13 17:20:01, Peter Zijlstra wrote:
> On Mon, Jul 29, 2013 at 04:53:08PM +0200, Michal Hocko wrote:
> > Peter, for you context the lockdep splat has been reported
> > here:
> >
> > Minchan has proposed to workaround it by using SINGLE_DEPTH_NESTING
> >
> >
> > my idea was to use a separate class key for hugetlb as it is quite
> > special in many ways:
> >
> >
> > What is the preferred way of fixing such an issue?
> The class is the safer annotation.

OK, I will use the class then. It should prevent other false positives

> That said; it is a rather horrible issue any which way. This PMD sharing
> is very unique to hugetlbfs (also is that really worth the effort these
> days?) and it will make it impossible to make hugetlbfs swappable.

No idea.

> The other solution is to make the pmd allocation GFP_NOFS.

That would be just papering over the lockdep limitation. So I would
rather stick with something lockdep specific.

I will cook up a patch.

Michal Hocko
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