Re: [PATCH 1/3] mm/memory_hotplug: Allow an override for the memmap_on_memory param

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Fri, 16 Jun 2023 09:46:59 +0200
David Hildenbrand <david@redhat.com> wrote:

> On 16.06.23 00:00, Vishal Verma wrote:
> > For memory hotplug to consider MHP_MEMMAP_ON_MEMORY behavior, the
> > 'memmap_on_memory' module parameter was a hard requirement.
> > 
> > In preparation for the dax/kmem driver to use memmap_on_memory
> > semantics, arrange for the module parameter check to be bypassed via the
> > appropriate mhp_flag.
> > 
> > Recall that the kmem driver could contribute huge amounts of hotplugged
> > memory originating from special purposes devices such as CXL memory
> > expanders. In some cases memmap_on_memory may be the /only/ way this new
> > memory can be hotplugged. Hence it makes sense for kmem to have a way to
> > force memmap_on_memory without depending on a module param, if all the
> > other conditions for it are met.  
> 
> Just let the admin configure it. After all, an admin is involved in 
> configuring the dax/kmem device to begin with. If add_memory() fails you 
> could give a useful hint to the admin.
> 

Agreed. If it were just the default then fine, but making it the only option
limits admin choices.

Jonathan