Re: [PATCH RFC 0/8] mm: online/offline 4MB chunks controlled by device driver

[David Hildenbrand <david@redhat.com>]

>>>> - Once all 4MB chunks of a memory block are offline, we can remove the
>>>>   memory block and therefore the struct pages (seems to work in my prototype),
>>>>   which is nice.
>>>
>>> OK, so our existing ballooning solutions indeed do not free up memmaps
>>> which is suboptimal.
>>
>> And we would have to hack deep into the current offlining code to make
>> it work (at least that's my understanding).
>>
>>>
>>>> Todo:
>>>> - We might have to add a parameter to offline_pages(), telling it to not
>>>>   try forever but abort in case it takes too long.
>>>
>>> Offlining fails when it see non-migrateable pages but other than that it
>>> should always succeed in the finite time. If not then there is a bug to
>>> be fixed.
>>
>> I just found the -EINTR in the offlining code and thought this might be
>> problematic. (e.g. if somebody pins a page that is still to be migrated
>> - or is that avoided by isolating?) I haven't managed to trigger this
>> scenario yet. Was just a thought, that's why I mentioned it but didn't
>> implement it.
> 
> Offlining is a 3 stage thing. Check for unmovable pages and fail with
> EBUSY, isolating free memory and migrating the rest. If the first 2
> succeed we expect the migration will finish in a finite time. 


BTW I was able to easily produce the case where do_migrate_range() would
loop for ever (well at least for multiple minutes, but I assume this
would have went on :) )


-- 

Thanks,

David / dhildenb