Re: [PATCH v1] drivers/base/memory.c: Don't store end_section_nr in memory blocks

[David Hildenbrand <david@redhat.com>]

On 31.07.19 16:37, Michal Hocko wrote:
> On Wed 31-07-19 16:21:46, David Hildenbrand wrote:
> [...]
>>> Thinking about it some more, I believe that we can reasonably provide
>>> both APIs controlable by a command line parameter for backwards
>>> compatibility. It is the hotplug code to control sysfs APIs.  E.g.
>>> create one sysfs entry per add_memory_resource for the new semantic.
>>
>> Yeah, but the real question is: who needs it. I can only think about
>> some DIMM scenarios (some, not all). I would be interested in more use
>> cases. Of course, to provide and maintain two APIs we need a good reason.
> 
> Well, my 3TB machine that has 7 movable nodes could really go with less
> than
> $ find /sys/devices/system/memory -name "memory*" | wc -l
> 1729>

The question is if it would be sufficient to increase the memory block
size even further for these kinds of systems (e.g., via a boot parameter
- I think we have that on uv systems) instead of having blocks of
different sizes. Say, 128GB blocks because you're not going to hotplug
128MB DIMMs into such a system - at least that's my guess ;)

> when it doesn't really make any sense to offline less than a
> hotremovable entity which is the whole node effectivelly. I have seen
> reports where a similarly large machine chocked on boot just because of
> too many udev events...>
> In other words allowing smaller granularity is a nice toy but real
> usecases usually work with the whole hotplugable entity (e.g. the whole
> ACPI container).

-- 

Thanks,

David / dhildenb