Re: [PATCH v12 04/22] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages

[John Hubbard]

On 1/16/20 1:37 AM, Christoph Hellwig wrote:
> On Wed, Jan 15, 2020 at 01:19:41PM -0800, John Hubbard wrote:
> > On 1/15/20 7:23 AM, Christoph Hellwig wrote:
> > ...
> > > I'm really not sold on this scheme.  Note that I think it is
> > > particularly bad, but it also doesn't seem any better than what
> > > we had before, and it introduced quite a bit more code.
> >
> > Hi Christoph,
> >
> > All by itself, yes. But the very next patch (which needs a little
> > rework for other reasons, so not included here) needs to reuse some of
> > these functions within __unpin_devmap_managed_user_page():
>
> Well, then combine it with the series that actually does the change.


OK, that makes sense. I just double-checked with a quick test run, that it
doesn't have dependencies with the rest of this series, and it came out clean,
so:

Andrew, could you please remove just this one patch from mmotm and linux-next?


> Also my vaguely recollection is that we had some idea on how to get rid
> of the off by one refcounting for the zone device pages, which would be
> a much better outcome.

Yes, I recall that Dan Williams mentioned it, but I don't think he provided
any details yet.


thanks,
--
John Hubbard
NVIDIA