On Tue, Jun 25, 2019 at 12:01 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > On Tue 25-06-19 11:03:53, Dan Williams wrote: > > On Tue, Jun 25, 2019 at 8:01 AM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > > > On Tue 25-06-19 09:23:17, Christoph Hellwig wrote: > > > > On Mon, Jun 24, 2019 at 11:24:48AM -0700, Dan Williams wrote: > > > > > I asked for this simply because it was not exported historically. In > > > > > general I want to establish explicit export-type criteria so the > > > > > community can spend less time debating when to use EXPORT_SYMBOL_GPL > > > > > [1]. > > > > > > > > > > The thought in this instance is that it is not historically exported > > > > > to modules and it is safer from a maintenance perspective to start > > > > > with GPL-only for new symbols in case we don't want to maintain that > > > > > interface long-term for out-of-tree modules. > > > > > > > > > > Yes, we always reserve the right to remove / change interfaces > > > > > regardless of the export type, but history has shown that external > > > > > pressure to keep an interface stable (contrary to > > > > > Documentation/process/stable-api-nonsense.rst) tends to be less for > > > > > GPL-only exports. > > > > > > > > Fully agreed. In the end the decision is with the MM maintainers, > > > > though, although I'd prefer to keep it as in this series. > > > > > > I am sorry but I am not really convinced by the above reasoning wrt. to > > > the allocator API and it has been a subject of many changes over time. I > > > do not remember a single case where we would be bending the allocator > > > API because of external modules and I am pretty sure we will push back > > > heavily if that was the case in the future. > > > > This seems to say that you have no direct experience of dealing with > > changing symbols that that a prominent out-of-tree module needs? GPU > > drivers and the core-mm are on a path to increase their cooperation on > > memory management mechanisms over time, and symbol export changes for > > out-of-tree GPU drivers have been a significant source of friction in > > the past. > > I have an experience e.g. to rework semantic of some gfp flags and that is > something that users usualy get wrong and never heard that an out of > tree code would insist on an old semantic and pushing us to the corner. > > > > So in this particular case I would go with consistency and export the > > > same way we do with other functions. Also we do not want people to > > > reinvent this API and screw that like we have seen in other cases when > > > external modules try reimplement core functionality themselves. > > > > Consistency is a weak argument when the cost to the upstream community > > is negligible. If the same functionality was available via another / > > already exported interface *that* would be an argument to maintain the > > existing export policy. "Consistency" in and of itself is not a > > precedent we can use more widely in default export-type decisions. > > > > Effectively I'm arguing EXPORT_SYMBOL_GPL by default with a later > > decision to drop the _GPL. Similar to how we are careful to mark sysfs > > interfaces in Documentation/ABI/ that we are not fully committed to > > maintaining over time, or are otherwise so new that there is not yet a > > good read on whether they can be made permanent. > > Documentation/process/stable-api-nonsense.rst That document has failed to preclude symbol export fights in the past and there is a reasonable argument to try not to retract functionality that had been previously exported regardless of that document. > Really. If you want to play with GPL vs. EXPORT_SYMBOL else this is up > to you but I do not see any technical argument to make this particular > interface to the page allocator any different from all others that are > exported to modules. I'm failing to find any practical substance to your argument, but in the end I agree with Chrishoph, it's up to MM maintainers.
