Re: [RFC Patch V1 07/30] mm: Use cpu_to_mem()/numa_mem_id() to support memoryless node

On Fri, 11 Jul 2014, Tejun Heo wrote:

> Hello,
>
> On Fri, Jul 11, 2014 at 03:37:24PM +0800, Jiang Liu wrote:
> > When CONFIG_HAVE_MEMORYLESS_NODES is enabled, cpu_to_node()/numa_node_id()
> > may return a node without memory, and later cause system failure/panic
> > when calling kmalloc_node() and friends with returned node id.
>
> The patch itself looks okay to me but is this the right way to handle
> this?  Can't we just let the allocators fall back to the nearest node
> with memory?  Why do we need to impose this awareness of memory-less
> node on all the users?

Allocators typically fall back but they wont in some cases if you say
that you want memory from a particular node. A GFP_THISNODE would force a
failure of the alloc. In other cases it should fall back. I am not sure
that all allocations obey these conventions though.