Re: [PATCH 5/6] mm, memory_hotplug: Provide argument for the pgprot_t in arch_add_memory()

From: Michal Hocko
Date: Wed Dec 11 2019 - 03:37:51 EST

On Tue 10-12-19 16:52:31, Logan Gunthorpe wrote:
> In my opinion, having a coder and reviewer see PAGE_KERNEL and ask if
> that makes sense is a benefit. Having it hidden because we don't want
> people to think about it is worse, harder to understand and results in
> bugs that are more difficult to spot.

My experience would disagree here. We have several examples in the MM
where an overly complex and versatile APIs led to suble bugs, a lot of
copy&pasting and cargo cult programing (just look at the page allocator
as a shiny example - e.g. gfp_flags). So I am always trying to be
carefull here.

> Though, we may be overthinking this: arch_add_memory() is a low level
> non-exported API that's currently used in exactly two places.

This is a fair argument. Most users are and should be using

> I don't
> think there's going to be many, if any, valid new use cases coming up
> for it in the future. That's more what memremap_pages() is for.

OK, fair enough. If this is indeed the simplest way forward then I will
not stand in the way.
Michal Hocko