[5.6.0-rc2-next-20200218/powerpc] Boot failure on POWER9

[David Rientjes]

On Wed, 26 Feb 2020, Michal Hocko wrote:

> On Wed 26-02-20 18:44:13, Cristopher Lameter wrote:
> > On Wed, 26 Feb 2020, Michal Hocko wrote:
> > 
> > > Besides that kmalloc_node shouldn't really have an implicit GFP_THISNODE
> > > semantic right? At least I do not see anything like that documented
> > > anywhere.
> > 
> > Kmalloc_node does not support memory policies etc. Only kmalloc does.
> > kmalloc_node is mostly used by subsystems that have determined the active
> > nodes and want a targeted allocation on those nodes.
>  
> I am sorry but I have hard time to follow your responses here. They open
> more questions than they answer for me. The primary point here is that
> kmalloc_node on a memory less node blows up and panics the kernel. I
> strongly believe this is a bug. We cannot really make all callers of
> kmalloc_node and co. to be hotplug aware.
> 
> Another question is the semantic of kmalloc_node when the node cannot
> satisfy the request. I have always thought that the allocation would
> simply fall back to any other node unless __GFP_THISNODE is explicitly
> specified.
> 

Am I right in classifying this as a trade-off between an 
unlikely(!node_state(nid, N_MEMORY)) directly in kmalloc_node() vs fixing 
up a caller passing a memoryless nid?

Seems like we wouldn't want to penalize kmalloc_node() for making such a 
check for 99.99% of allocators that don't need it and would rather do a 
node_to_mem_node(nid) or numa_mem_id() in the caller?