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SubjectRe: [PATCH v6 06/12] mm/hotplug: Add mem-hotplug restrictions for remove_memory()
On Tue, Apr 23, 2019 at 2:21 PM David Hildenbrand <david@redhat.com> wrote:
>
> On 17.04.19 20:39, Dan Williams wrote:
> > Teach the arch_remove_memory() path to consult the same 'struct
> > mhp_restrictions' context as was specified at arch_add_memory() time.
> >
> > No functional change, this is a preparation step for teaching
> > __remove_pages() about how and when to allow sub-section hot-remove, and
> > a cleanup for an unnecessary "is_dev_zone()" special case.
>
> I am not yet sure if this is the right thing to do. When adding memory,
> we obviously have to specify the "how". When removing memory, we usually
> should be able to look such stuff up.

True, the implementation can just use find_memory_block(), and no need
to plumb this flag.

>
>
> > void __remove_pages(struct zone *zone, unsigned long phys_start_pfn,
> > - unsigned long nr_pages, struct vmem_altmap *altmap)
> > + unsigned long nr_pages, struct mhp_restrictions *restrictions)
> > {
> > unsigned long i;
> > - unsigned long map_offset = 0;
> > int sections_to_remove;
> > + unsigned long map_offset = 0;
> > + struct vmem_altmap *altmap = restrictions->altmap;
> >
> > - /* In the ZONE_DEVICE case device driver owns the memory region */
> > - if (is_dev_zone(zone)) {
> > - if (altmap)
> > - map_offset = vmem_altmap_offset(altmap);
> > - }
> > + if (altmap)
> > + map_offset = vmem_altmap_offset(altmap);
> >
>
> Why weren't we able to use this exact same hunk before? (after my
> resource deletion cleanup of course)
>
> IOW, do we really need struct mhp_restrictions here?

We don't need it. It was only the memblock info why I added the
"restrictions" argument.

> After I factor out memory device handling into the caller of
> arch_remove_memory(), also the next patch ("mm/sparsemem: Prepare for
> sub-section ranges") should no longer need it. Or am I missing something?

That patch is still needed for the places where it adds the @nr_pages
argument, but the mhp_restrictions related bits can be dropped. The
subsection_check() helper needs to be refactored a bit to not rely on
mhp_restrictions.

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