Re: [PATCH v2 0/2] mm: Memory offlining + page isolation cleanups

[David Hildenbrand <david@redhat.com>]

On 22.10.19 10:08, Michal Hocko wrote:
> On Tue 22-10-19 08:52:28, David Hildenbrand wrote:
>> On 21.10.19 19:23, David Hildenbrand wrote:
>>> Two cleanups that popped up while working on (and discussing) virtio-mem:
>>>    https://lkml.org/lkml/2019/9/19/463
>>>
>>> Tested with DIMMs on x86.
>>>
>>> As discussed with michal in v1, I'll soon look into removing the use
>>> of PG_reserved during memory onlining completely - most probably
>>> disallowing to offline memory blocks with holes, cleaning up the
>>> onlining+offlining code.
>>
>> BTW, I remember that ZONE_DEVICE pages are still required to be set
>> PG_reserved. That has to be sorted out first.
> 
> Do they?

Yes, especially KVM code :/

> 
>> I remember that somebody was
>> working on it a while ago but didn't hear about that again. Will look into
>> that as well - should be as easy as adding a zone check (if there isn't a
>> pfn_to_online_page() check already). But of course, there might be special
>> cases ....
> 
> I remember Alexander didn't want to change the PageReserved handling
> because he was worried about unforeseeable side effects. I have a vague
> recollection he (or maybe Dan) has promissed some follow up clean ups
> which didn't seem to materialize.

I'm looking into it right now, especially the KVM part.

-- 

Thanks,

David / dhildenb