[Ksummit-discuss] ZONE_DEVICE and Persistent Memory (was: Re: Draft agenda for the kernel summit)

[Dan Williams]

On Mon, Oct 12, 2015 at 12:01 PM, Theodore Ts'o <tytso at mit.edu> wrote:
> This is an initial draft for the upcoming kernel summit.
>
> It is still very drafty; in particular, just because a topic has been
> listed, it may turn out that the topic has been resolved off-line, or
> otherwise overtaken by events, in which case we will drop it.  In
> addition, we're also in the process of sending queries to the proposed
> topic leaders to see if they are willing to kick off the discussion,
> and so that is subject to change as well.
>
> I'd appreciate comments about any topics that you think might be
> missing and that would be worth our discussing.

I am wondering if it would be productive / good use of time to do a
direction check on the mm changes being done in support of large
persistent memory devices.  The new ZONE_DEVICE mm-zone was added in a
basic form in 4.3 [1].  The follow-on patches to make use of it have
not enjoyed much feedback to date, especially compared to the debate
that occurred when removing struct page from the block-layer was being
considered [2].

I'm assuming either the new approach is sufficiently non-controversial
and this is just normal patch review latency, or there are some
brewing discussion topics that might make forward progress in person.
One example might be unintended usages of devm_memremap_pages() as
some are experimenting with it to enable peer-to-peer PCI-E transfers.
Another might be the future of the effort to reduce the usage of, or
redefine, struct page.

[1]: https://git.kernel.org/cgit/linux/kernel/git/nvdimm/nvdimm.git/tag/?id=libnvdimm-for-4.3
[2]: https://lists.01.org/pipermail/linux-nvdimm/2015-May/000748.html