linux-kernel - Re: [PATCH v7 0/7] mm: Merge hmm into devm_memremap

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Date:   Fri, 12 Oct 2018 14:14:25 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     akpm@...ux-foundation.org, stable@...r.kernel.org,
        Balbir Singh <bsingharora@...il.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Christoph Hellwig <hch@....de>, Michal Hocko <mhocko@...e.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 0/7] mm: Merge hmm into devm_memremap_pages, mark
 GPL-only

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.
> 
> [1]: https://lkml.org/lkml/2018/9/13/104
> 
> ---
> 
> 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.
> 
> [2]: https://www.lkml.org/lkml/2018/9/11/10

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