Re: [PATCH v7 4/8] mm,memory_hotplug: Allocate memmap from the added memory range

[David Hildenbrand]

On 16.04.21 09:25, Oscar Salvador wrote:
> On Thu, Apr 15, 2021 at 01:19:59PM +0200, David Hildenbrand wrote:
> > > Implementation wise we will reuse vmem_altmap infrastructure to override
> > > the default allocator used by __populate_section_memmap.
> > > Part of the implementation also relies on memory_block structure gaining
> > > a new field which specifies the number of vmemmap_pages at the beginning.
> > > This patch also introduces the following functions:
> > >
> > >    - vmemmap_init_space: Initializes vmemmap pages by calling move_pfn_range_to_zone(),
> > > 		       calls kasan_add_zero_shadow() or the vmemmap range and marks
> > > 		       online as many sections as vmemmap pages fully span.
> > >    - vmemmap_adjust_pages: Accounts/substract vmemmap_pages to node and zone
> > > 			 present_pages
> > >    - vmemmap_deinit_space: Undoes what vmemmap_init_space does.
> >
> > This is a bit asynchronous; and the function names are not really expressing what is being done :) I'll try to come up with better names below.
>
> Yeah, was not happy either with the names but at that time I could not
> come up with anything better.
>
> > It is worth mentioning that the real "mess" is that we want offline_pages() to properly handle zone->present_pages going to 0. Therefore, we want to manually mess with the present page count.
>
> This should be explained by this:
>
> "On offline, memory_block_offline() calls vmemmap_adjust_pages() prior to calling
> offline_pages(), because offline_pages() performs the tearing-down of kthreads
> and the rebuilding of the zonelists if the node/zone become empty."
>
> Is not that clear?

Ehm, it is; for some reason my eyes ignored it -- sorry.

--
Thanks,

David / dhildenb