On Wed, 17 Apr 2019 11:38:55 -0700 Dan Williams <dan.j.williams(a)intel.com> wrote:
The memory hotplug section is an arbitrary / convenient unit for
hotplug. 'Section-size' units have bled into the user interface
('memblock' sysfs) and can not be changed without breaking existing
userspace. The section-size constraint, while mostly benign for typical
memory hotplug, has and continues to wreak havoc with 'device-memory'
use cases, persistent memory (pmem) in particular. Recall that pmem uses
devm_memremap_pages(), and subsequently arch_add_memory(), to allocate a
'struct page' memmap for pmem. However, it does not use the 'bottom
half' of memory hotplug, i.e. never marks pmem pages online and never
exposes the userspace memblock interface for pmem. This leaves an
opening to redress the section-size constraint.
v6 and we're not showing any review activity. Who would be suitable
people to help out here?