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
