Re: [PATCH 0/6] mm: make movable onlining suck less

[Michal Hocko <mhocko@kernel.org>]

On Tue 04-04-17 09:34:12, Michal Hocko wrote:
> On Tue 04-04-17 09:23:29, Michal Hocko wrote:
> > [Let's add Gary who as introduced this code c04fc586c1a48]
> 
> OK, so Gary's email doesn't exist anymore. Does anybody can comment on
> this? I suspect this code is just-in-case... Mel?
>  
> > On Mon 03-04-17 15:42:13, Reza Arbab wrote:
> [...]
> > > Almost there. I'm seeing the memory in the correct node now, but the
> > > /sys/devices/system/node/nodeX/memoryY links are not being created.
> > > 
> > > I think it's tripping up here, in register_mem_sect_under_node():
> > > 
> > > 		page_nid = get_nid_for_pfn(pfn);
> > > 		if (page_nid < 0)
> > > 			continue;
> > 
> > Huh, this code is confusing. How can we have a memblock spanning more
> > nodes? If not then the loop over all sections in the memblock seem
> > pointless as well.  Also why do we require page_initialized() in
> > get_nid_for_pfn? The changelog doesn't explain that and there are no
> > comments that would help either.

OK, so I've been thinkin about that and I believe that page_initialized
check in get_nid_for_pfn is just bogus. There is nothing to rely on the
page::lru to be already initialized. So I will go with the following as
a separate preparatory patch.

I believe the whole code should be revisited and I have put that on my
ever growing todo list because I suspect that it is more complex than
necessary. I suspect that memblock do not span more nodes and all this
is just-in-case code (e.g. the onlining code assumes a single zone aka
node. But let's do that later.

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