Re: [PATCH v1 0/4] smaps / mm/gup: fix gup_can_follow_protnone fallout

[John Hubbard]

On 7/28/23 14:20, Peter Xu wrote:
> On Fri, Jul 28, 2023 at 11:02:46PM +0200, David Hildenbrand wrote:
> > Can we get a simple revert in first (without that FOLL_FORCE special casing
> > and ideally with a better name) to handle stable backports, and I'll
> > follow-up with more documentation and letting GUP callers pass in that flag
> > instead?
> >
> > That would help a lot. Then we also have more time to let that "move it to
> > GUP callers" mature a bit in -next, to see if we find any surprises?
>
> As I raised my concern over the other thread, I still worry numa users can
> be affected by this change. After all, numa isn't so uncommon to me, at
> least fedora / rhel as CONFIG_NUMA_BALANCING_DEFAULT_ENABLED=y. I highly
> suspect that's also true to major distros.  Meanwhile all kernel modules
> use gup..
>
> I'd say we can go ahead and try if we want, but I really don't know why
> that helps in any form to move it to the callers.. with the risk of
> breaking someone.

It's worth the trouble, in order to clear up this historical mess. It's
helping *future* callers of the API, and future maintenance efforts. Yes
there is some risk, but it seems very manageable.

The story of how FOLL_NUMA and FOLL_FORCE became entangled was enlightening,
by the way, and now that I've read it I don't want to go back. :)


thanks,
--
John Hubbard
NVIDIA