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Re: [PATCH v4 00/13] mm: sub-section memory hotplug support

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On Thu, Mar 16, 2017 at 10:48 AM, Michal Hocko <mhocko@kernel.org> wrote:
> Hi,
> I didn't get to look through the patch series yet and I might not be
> able before LSF/MM. How urgent is this? I am primarily asking because
> the memory hotplug is really convoluted right now and putting more on
> top doesn't really sound like the thing we really want. I have tried to
> simplify the code [1] already but this is an early stage work so I do
> not want to impose any burden on you. So I am wondering whether this
> is something that needs to be merged very soon or it can wait for the
> rework and hopefully end up being much simpler in the end as well.
>
> What do you think?

In general, I think it's better to add new features after
reworks/cleanup, but it's not clear to me (yet) that the problem you
are trying to solve makes this sub-section enabling for ZONE_DEVICE
any simpler.

> [1] http://lkml.kernel.org/r/20170315091347.GA32626@dhcp22.suse.cz

ZONE_DEVICE pages are never "online". The patch says "Instead we do
page->zone association from move_pfn_range which is called from
online_pages." which means the new scheme currently doesn't comprehend
the sprinkled ZONE_DEVICE hacks in the memory hotplug code.

However, that said, I might take a look at whether the hacks belong in
the auto-online code so that we can share the delayed zone
initialization, but still skip marking the memory online per the
expectations of ZONE_DEVICE. I expect it would be confusing to have
memblock devices in sysfs for ranges that can't be marked online?

Thoughts?

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[PATCH v4 00/13] mm: sub-section memory hotplug support Dan Williams <dan.j.williams@intel.com> - 2017-03-16 07:20 +0100
  [PATCH v4 07/13] mm: fix register_new_memory() zone type detection Dan Williams <dan.j.williams@intel.com> - 2017-03-16 07:20 +0100
  [PATCH v4 10/13] mm: prepare for hot-{add,  remove} of sub-section ranges Dan Williams <dan.j.williams@intel.com> - 2017-03-16 07:20 +0100
  [PATCH v4 06/13] mm: track active portions of a section at boot Dan Williams <dan.j.williams@intel.com> - 2017-03-16 07:20 +0100
  [PATCH v4 12/13] mm: enable section-unaligned devm_memremap_pages() Dan Williams <dan.j.williams@intel.com> - 2017-03-16 07:20 +0100
  [PATCH v4 11/13] mm: support section-unaligned ZONE_DEVICE memory  ranges Dan Williams <dan.j.williams@intel.com> - 2017-03-16 07:20 +0100
  [PATCH v4 05/13] mm: cleanup sparse_init_one_section() return value Dan Williams <dan.j.williams@intel.com> - 2017-03-16 07:20 +0100
  [PATCH v4 01/13] mm: fix type width of section to/from pfn  conversion macros Dan Williams <dan.j.williams@intel.com> - 2017-03-16 07:20 +0100
  [PATCH v4 09/13] mm: convert kmalloc_section_memmap() to  populate_section_memmap() Dan Williams <dan.j.williams@intel.com> - 2017-03-16 07:20 +0100
  [PATCH v4 02/13] mm,  devm_memremap_pages: use multi-order radix for ZONE_DEVICE lookups Dan Williams <dan.j.williams@intel.com> - 2017-03-16 07:20 +0100
  [PATCH v4 03/13] mm: introduce struct mem_section_usage to track  partial population of a section Dan Williams <dan.j.williams@intel.com> - 2017-03-16 07:20 +0100
  [PATCH v4 04/13] mm: introduce common definitions for the size and  mask of a section Dan Williams <dan.j.williams@intel.com> - 2017-03-16 07:20 +0100
  [PATCH v4 13/13] libnvdimm, pfn,  dax: stop padding pmem namespaces to section alignment Dan Williams <dan.j.williams@intel.com> - 2017-03-16 07:20 +0100
  [PATCH v4 08/13] x86,  kasan: clarify kasan's dependency on vmemmap_populate_hugepages() Dan Williams <dan.j.williams@intel.com> - 2017-03-16 07:20 +0100
  Re: [PATCH v4 00/13] mm: sub-section memory hotplug support Michal Hocko <mhocko@kernel.org> - 2017-03-16 18:50 +0100
    Re: [PATCH v4 00/13] mm: sub-section memory hotplug support Dan Williams <dan.j.williams@intel.com> - 2017-03-16 20:10 +0100
      Re: [PATCH v4 00/13] mm: sub-section memory hotplug support Michal Hocko <mhocko@kernel.org> - 2017-03-19 18:00 +0100

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