On Tue, May 29, 2018 at 04:33:49PM -0700, Dan Williams wrote: > 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. I am personaly on the fence on deciding GPL versus non GPL export base on subjective view of what is deeply integrated and what is not. I think one can argue that every single linux kernel function is deeply integrated within the kernel, starting with all device drivers functions. One could similarly argue that nothing is ... I see more value in consistency of symbol export over time. Once we pick one it should stay that way. > >> 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. While HMM is a toolbox and i intend to use some part of HMM to replace some existing GUP user. Biggest user of HMM will use all the tools in the HMM box. Thus having a mix of GPL and non GPL defeat its usefulness for out of tree drivers. I still want to review this patchset, i am going through a backlog of urgent emails so i probably won't be able to review before a day or two. I am just strongly against changing to GPL only export. Cheers, Jérôme
