On Fri, Oct 12, 2018 at 10:49:31AM -0700, Dan Williams wrote:
[ apologies for the resend, script error ]
Changes since v6 [1]:
- Rebase on next-20181008 and fixup conflicts with the xarray conversion and hotplug optimizations
- It has soaked on a 0day visible branch for a few days without any reports.
Hi Andrew,
Jérôme has reviewed the cleanups, thanks Jérôme. We still disagree on the EXPORT_SYMBOL_GPL status of the core HMM implementation, but Logan, Christoph and I continue to support marking all devm_memremap_pages() derivatives EXPORT_SYMBOL_GPL.
HMM has been upstream for over a year, with no in-tree users it is clear it was designed first and foremost for out of tree drivers. It takes advantage of a facility Christoph and I spearheaded to support persistent memory. It continues to see expanding use cases with no clear end date when it will stop attracting features / revisions. It is not suitable to export devm_memremap_pages() as a stable 3rd party driver api.
devm_memremap_pages() is a facility that can create struct page entries for any arbitrary range and give out-of-tree drivers the ability to subvert core aspects of page management. It, and anything derived from it (e.g. hmm, pcip2p, etc...), is a deep integration point into the core kernel, and an EXPORT_SYMBOL_GPL() interface.
Commit 31c5bda3a656 "mm: fix exports that inadvertently make put_page() EXPORT_SYMBOL_GPL" was merged ahead of this series to relieve some of the pressure from innocent consumers of put_page(), but now we need this series to address *producers* of device pages.
More details and justification in the changelogs. The 0day infrastructure has reported success across 152 configs and this survives the libnvdimm unit test suite. Aside from the controversial bits the diffstat is compelling at:
7 files changed, 126 insertions(+), 323 deletions(-)
Note that the series has some minor collisions with Alex's recent series to improve devm_memremap_pages() scalability [2]. So, whichever you take first the other will need a minor rebase.
I am fine with this patchset going in (i reviewed it and tested it with HMM on nouveau), Dan and Christoph did author the original code around devm_memremap_pages() and thus ultimately they are the one who should decide over GPL export or not.
Cheers, Jérôme