linux-kernel - Re: BUG: mm, numa: test segfaults, only when NUMA balancing is on

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Date:	Wed, 27 Nov 2013 17:58:16 -0600
From:	Alex Thorlton <athorlton@....com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Rik van Riel <riel@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: BUG: mm, numa: test segfaults, only when NUMA balancing is on

On Sat, Nov 23, 2013 at 12:09:24AM +0000, Mel Gorman wrote:
> On Fri, Nov 22, 2013 at 11:05:24PM +0000, Mel Gorman wrote:
> > On Fri, Nov 22, 2013 at 03:28:07PM -0600, Alex Thorlton wrote:
> > > > If the warning added by that patch does *not* trigger than can you also
> > > > test this patch? It removes the barriers which should not be necessary
> > > > and takes a reference tot he page before waiting on the lock. The
> > > > previous version did not take the reference because otherwise the
> > > > WARN_ON could not distinguish between a migration waiter and a surprise
> > > > gup.
> > > 
> > > Sorry for the delay; been a bit busy.  I tested both of these patches on
> > > top of this one (separately, of course):
> > > 
> > > http://www.spinics.net/lists/linux-mm/msg63919.html
> > > 
> > > I think that's the one you were referring to, if not send me a pointer
> > > to the correct one and I'll give it another shot.  Both patches still
> > > segfaulted, so it doesn't appear that either of these solved the
> > > problem. 
> > 
> > I see. Does THP have to be enabled or does it segfault even with THP
> > disabled?

It occurs with both THP on, and off.  I get RCU stalls with THP on
though.  That's probably related to not having Kirill/Naoya's patches
applied though.

> > 
> 
> On a semi-related note, is the large machine doing anything with xpmem
> or anything that depends on MMU notifiers to work properly? I noted
> while looking at this that THP migration is not invalidating pages which
> might be confusing a driver depending on it.

I'm not using xpmem on any of the machines that I've been testing on,
and I don't think that anything should be using MMU notifiers.

- Alex
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