On Thu, 30 Nov 2017 07:53:35 +0100 Michal Hocko <mho...@kernel.org> wrote:
> > mm... So we have a caller which hopes to be getting highmem pages but > > isn't. Caller then proceeds to pointlessly kmap the page and wonders > > why it isn't getting as much memory as it would like on 32-bit systems, > > etc. > > How he can kmap the page when he gets a _virtual_ address? doh. > > I do think we should help ferret out such bogosity. A WARN_ON_ONCE > > would suffice. > > This function has always been about lowmem pages. I seriously doubt we > have anybody confused and asking for a highmem page in the kernel. I > haven't checked that but it would already blow up as VM_BUG_ON tends to > be enabled on many setups. OK. But silently accepting __GFP_HIGHMEM is a bit weird - callers shouldn't be doing that in the first place. I wonder what happens if we just remove the WARN_ON and pass any __GFP_HIGHMEM straight through. The caller gets a weird address from page_to_virt(highmem page) and usually goes splat? Good enough treatment for something which never happens anyway?
