Problems with swapping in v4.5-rc on POWER

[Hugh Dickins]

On Thu, 25 Feb 2016, Hugh Dickins wrote:
> On Wed, 24 Feb 2016, Hugh Dickins wrote:
> > On Thu, 25 Feb 2016, Aneesh Kumar K.V wrote:
> > > 
> > > Can you test the impact of the merge listed below ?(ie, revert the merge and see if
> > > we can reproduce and also verify with merge applied). This will give us a
> > > set of commits to look closer. We had quiet a lot of page table
> > > related changes going in this merge window. 
> > > 
> > > f689b742f217b2ffe7 ("Pull powerpc updates from Michael Ellerman:")
> > > 
> > > That is the merge commit that added _PAGE_PTE. 
> > 
> > Another experiment running on it at the moment, I'd like to give that
> > a few more hours, and then will try the revert you suggest.  But does
> > that merge revert cleanly, did you try?  I'm afraid of interactions,
> > whether obvious or subtle, with the THP refcounting rework.  Oh, since
> > I don't have THP configured on, maybe I can ignore any issues from that.
> 
> That revert worked painlessly, only a very few and simple conflicts,
> I ran that under load for 12 hours, no problem seen.
> 
> I've now checked out an f689b742 tree and started on that, just to
> confirm that it fails fairly quickly I hope; and will then proceed
> to git bisect, giving that as bad and 37cea93b as good.
> 
> Given the uncertainty of whether 12 hours is really long enough to be
> sure, and perhaps difficulties along the way, I don't rate my chances
> of a reliable bisection higher than 60%, but we'll see.

I'm sure you won't want a breathless report from me on each bisection
step, but I ought to report that: contrary to our expectations, the
f689b742 survived without error for 12 hours, so appears to be good.
I'll bisect between there and v4.5-rc1.

Hugh