On Tue, May 29, 2018 at 4:00 PM, Dave Airlie <airlied@xxxxxxxxx> wrote: > On 30 May 2018 at 08:31, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: >> On Tue, May 29, 2018 at 3:22 PM, Dave Airlie <airlied@xxxxxxxxx> wrote: >>> >>> On 24 May 2018 at 13:18, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: >>> > On Wed, May 23, 2018 at 5:10 PM, Jerome Glisse <jglisse@xxxxxxxxxx> wrote: >>> >> On Mon, May 21, 2018 at 03:35:14PM -0700, Dan Williams wrote: >>> >>> Hi Andrew, please consider this series for 4.18. >>> >>> >>> >>> For maintainability, as ZONE_DEVICE continues to attract new users, >>> >>> it is useful to keep all users consolidated on devm_memremap_pages() as >>> >>> the interface for create "device pages". >>> >>> >>> >>> The devm_memremap_pages() implementation was recently reworked to make >>> >>> it more generic for arbitrary users, like the proposed peer-to-peer >>> >>> PCI-E enabling. HMM pre-dated this rework and opted to duplicate >>> >>> devm_memremap_pages() as hmm_devmem_pages_create(). >>> >>> >>> >>> Rework HMM to be a consumer of devm_memremap_pages() directly and fix up >>> >>> the licensing on the exports given the deep dependencies on the mm. >>> >> >>> >> I am on PTO right now so i won't be able to quickly review it all >>> >> but forcing GPL export is problematic for me now. I rather have >>> >> device driver using "sane" common helpers than creating their own >>> >> crazy thing. >>> > >>> > Sane drivers that need this level of deep integration with Linux >>> > memory management need to be upstream. Otherwise, HMM is an >>> > unprecedented departure from the norms of Linux kernel development. >>> >>> Isn't it the author of code choice what EXPORT_SYMBOL to use? and >>> isn't the agreement that if something is EXPORT_SYMBOL now, changing >>> underlying exports isn't considered a good idea. We've seen this before >>> with the refcount fun, >>> >>> See d557d1b58b3546bab2c5bc2d624c5709840e6b10 >>> >>> Not commenting on the legality or what derived works are considered, >>> since really the markings are just an indication of the authors opinion, >>> and at this stage I think are actually meaningless, since we've diverged >>> considerably from the advice given to Linus back when this started. >> >> Yes, and in this case devm_memremap_pages() was originally written by >> Christoph and I: >> >> 41e94a851304 add devm_memremap_pages > > So you wrote some code in 2015 (3 years ago) and you've now decided > to change the EXPORT marker on it? what changed in 3 years, and why > would changing that marker 3 years later have any effect on your original > statement that it was an EXPORT_SYMBOL. > > Think what EXPORT_SYMBOL vs GPL means, it isn't a bit stick that magically > makes things into derived works. If something wasn't a derived work for 3 years > using that API, then it isn't a derived work now 3 years later because you > changed the marker. Retrospectively changing the markers doesn't really > make any sense legally or otherwise. It honestly was an oversight, and as we've gone on to add deeper and deeper ties into the mm and filesystems [1] I realized this symbol was mis-labeled. It would be one thing if this was just some random kernel leaf / library function, but this capability when turned on causes the entire kernel to be recompiled as things like the definition of put_page() changes. It's deeply integrated with how Linux manages memory. >> HMM started off by duplicating devm_memremap_pages() which is fixed up >> by this series: > > Just looking in my current tree hmm_devmem_pages_create and > devm_memremap_pages don't look like duplicates, they might have > code but they definitely aren't one for one copies. I'm not sure you can > just say Jerome copied that code in, you've now refactored the code > so HMM can use it and are changing the symbol exports underneath it, The initial patches for HMM used devm_memremap_pages() directly, and during review I asked for the exact same arrangement as implemented here, i.e. for the dev_pagemap structure to be a sub-structure of the HMM data [2]. At some point along the way we lost that review feedback. It was not until Christoph and Logan recently reworked devm_memermap_pages() that I realized that HMM had unnecessarily diverged. > Again if Christoph believes all uses of this are a derived work he didn't > indicate it 3 years ago, but neither does the mark make any legal difference > in this case, since everything in the kernel is GPL, and if you > consider something > a derived work or not is well into legal land. > > I'd rather anyways the original author of HMM wishes were respected > on his code, or at least you wait until he gets back from holidays before > pushing to merge this. To be clear this only affects the usage of the ZONE_DEVICE facility, I'm not touching the other pieces of HMM that are original to HMM. I didn't realize Jerome was on vacation when I sent the patches, and I think it is otherwise healthy to have this discussion in the meantime. [1]: https://lists.01.org/pipermail/linux-nvdimm/2018-May/015905.html [2]: http://lkml.iu.edu/hypermail/linux/kernel/1701.2/00812.html
