Re: [RFC PATCH] rework memory hotplug onlining

[Dan Williams]

On Fri, Mar 17, 2017 at 6:20 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> On Wed 15-03-17 10:13:47, Michal Hocko wrote:
> [...]
>> It seems that all this is just started by the semantic introduced by
>> 9d99aaa31f59 ("[PATCH] x86_64: Support memory hotadd without sparsemem")
>> quite some time ago. When the movable onlinining has been introduced it
>> just built on top of this. It seems that the requirement to have
>> freshly probed memory associated with the zone normal is no longer
>> necessary. HOTPLUG depends on CONFIG_SPARSEMEM these days.
>>
>> The following blob [2] simply removes all the zone specific operations
>> from __add_pages (aka arch_add_memory) path.  Instead we do page->zone
>> association from move_pfn_range which is called from online_pages. The
>> criterion for movable/normal zone association is really simple now. We
>> just have to guarantee that zone Normal is always lower than zone
>> Movable. It would be actually sufficient to guarantee they do not
>> overlap and that is indeed trivial to implement now. I didn't do that
>> yet for simplicity of this change though.
>
> Does anybody have any comments on this? Any issues I've overlooked
> (except for the one pointed by Toshi Kani which is already fixed in my
> local branch)?

It disables the ZONE_DEVICE use case, but like we chatted about at LSF
I'll take a look at having devm_memremap_pages() call
move_pfn_range().