Re: [PATCH] mm: page_alloc: don't allocate page from memoryless nodes

[David Hildenbrand]

On 14.02.23 12:48, David Hildenbrand wrote:
> On 14.02.23 12:44, Mike Rapoport wrote:
> > (added x86 folks)
> >
> > On Tue, Feb 14, 2023 at 12:29:42PM +0100, David Hildenbrand wrote:
> > > On 14.02.23 12:26, Qi Zheng wrote:
> > > > On 2023/2/14 19:22, David Hildenbrand wrote:
> > > > > TBH, this is the first time I hear of NODE_MIN_SIZE and it seems to be a
> > > > > pretty x86 specific thing.
> > > > >
> > > > > Are we sure we want to get NODE_MIN_SIZE involved?
> > > >
> > > > Maybe add an arch_xxx() to handle it?
> > >
> > > I still haven't figured out what we want to achieve with NODE_MIN_SIZE at
> > > all. It smells like an arch-specific hack looking at
> > >
> > > "Don't confuse VM with a node that doesn't have the minimum amount of
> > > memory"
> > >
> > > Why shouldn't mm-core deal with that?
> >
> > Well, a node with <4M RAM is not very useful and bears all the overhead of
> > an extra live node.
>
> And totally not with 4.1M, haha.
>
> I really like the "Might fix boot" in the commit description.
>
> > But, hey, why won't we just drop that '< NODE_MIN_SIZE' and let people with
> > weird HW configurations just live with this?
>
>
> ;)

Actually, remembering 09f49dca570a ("mm: handle uninitialized numa nodes 
gracefully"), this might be the right thing to do. That commit assumes 
that all offline nodes would get the pgdat allocated in 
free_area_init(). So that we end up with an allocated pgdat for all 
possible nodes. The reasoning IIRC was that we don't care about wasting 
memory in weird VM setups.

CCing Michal.

--
Thanks,

David / dhildenb