Re: [PATCH V3 1/3] mm/memory_hotplug: Prevalidate the address range being added with platform

From: Oscar Salvador
Date: Wed Jan 20 2021 - 07:19:34 EST

On Wed, Jan 20, 2021 at 11:41:53AM +0100, David Hildenbrand wrote:
> On 20.01.21 09:33, Anshuman Khandual wrote:
> >
> >
> > On 1/19/21 5:51 PM, David Hildenbrand wrote:
> >> On 18.01.21 14:12, Anshuman Khandual wrote:
> >>> This introduces memhp_range_allowed() which can be called in various memory
> >>> hotplug paths to prevalidate the address range which is being added, with
> >>> the platform. Then memhp_range_allowed() calls memhp_get_pluggable_range()
> >>> which provides applicable address range depending on whether linear mapping
> >>> is required or not. For ranges that require linear mapping, it calls a new
> >>> arch callback arch_get_mappable_range() which the platform can override. So
> >>> the new callback, in turn provides the platform an opportunity to configure
> >>> acceptable memory hotplug address ranges in case there are constraints.
> >>>
> >>> This mechanism will help prevent platform specific errors deep down during
> >>> hotplug calls. This drops now redundant check_hotplug_memory_addressable()
> >>> check in __add_pages() but instead adds a VM_BUG_ON() check which would
> >>
> >> In this patch, you keep the __add_pages() checks. But as discussed, we
> >> could perform it in mm/memremap.c:pagemap_range() insted and convert it
> >> to a VM_BUG_ON().
> >
> > Just to be sure, will the following change achieve what you are
> > suggesting here. pagemap_range() after this change, will again
> > be the same like the V1 series.
> Yeah, as we used to have in v1. Maybe other reviewers (@Oscar?) have a
> different opinion.

No, I think that placing the check in pagemap_range() out of the if-else
makes much more sense.
Actually, unless my memory fails me that is what I suggested in v2.

I plan to have a look at the series later this week as I am fairly busy


Oscar Salvador