Re: [PATCH 2/2] mm, memory_hotplug: remove zone restrictions

[Michal Hocko]

On Mon 10-07-17 14:12:09, Vlastimil Babka wrote:
> On 07/10/2017 01:17 PM, Michal Hocko wrote:
> > On Mon 10-07-17 13:11:29, Vlastimil Babka wrote:
> >> On 07/10/2017 08:45 AM, Michal Hocko wrote:
> >>> On Fri 07-07-17 17:02:59, Vlastimil Babka wrote:
> >>>> [+CC linux-api]
> >>>>
> >>>>
> >>>> Hm so previously, blocks 37-41 would only allow Movable at this point, right?
> >>>
> >>> yes
> >>>
> >>>> Shouldn't we still default to Movable for them? We might be breaking some
> >>>> existing userspace here.
> >>>
> >>> I do not think so. Prior to this merge window f1dd2cd13c4b ("mm,
> >>> memory_hotplug: do not associate hotadded memory to zones until online")
> >>> we allowed only the last offline or the adjacent to existing movable
> >>> memory block to be onlined movable. So the above wasn't possible.
> >>
> >> Not exactly the above, but let's say 1-34 is onlined as Normal, 35-37 is
> >> Movable. Then the only possible action before would be online 38 as
> >> Movable? Now it defaults to Normal?
> > 
> > Yes. And let me repeat you couldn't onlne 35-37 as movable before. So no
> > userspace could depend on that before the rework. Or do I still miss
> > your point?
> 
> Ah, I see. "the last offline or the adjacent to existing movable". OK then.
> 
> It would be indeed better to not change behavour twice then and merge
> this to 4.13, but it's the middle of merge window, so it's not simple...

yeah. I was thinking about about how to make the change reasonably
incremental but failed to find a way. I also didn't want to bring too
many changes at once (the code base is just too fragile already).

If there is a general consensus about the semantic we might want to push
the patch this week. I just do not want to rush it too much as this is a
users visible change and it might kick us back in future.
-- 
Michal Hocko
SUSE Labs