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SubjectRe: [PATCH v5 1/5] mm,memory_hotplug: Allocate memmap from the added memory range
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Tow NITs

> +bool mhp_supports_memmap_on_memory(unsigned long size)
> +{
> + unsigned long nr_vmemmap_pages = size / PAGE_SIZE;
> + unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page);
> + unsigned long remaining_size = size - vmemmap_size;
> +
> + /*
> + * Besides having arch support and the feature enabled at runtime, we
> + * need a few more assumptions to hold true:
> + *
> + * a) We span a single memory block: memory onlining/offlinin;g happens

s/offlinin;g/offlining;/

> + * in memory block granularity. We don't want the vmemmap of online
> + * memory blocks to reside on offline memory blocks. In the future,
> + * we might want to support variable-sized memory blocks to make the
> + * feature more versatile.
> + *
> + * b) The vmemmap pages span complete PMDs: We don't want vmemmap code
> + * to populate memory from the altmap for unrelated parts (i.e.,
> + * other memory blocks)
> + *
> + * c) The vmemmap pages (and thereby the pages that will be exposed to
> + * the buddy) have to cover full pageblocks: memory onlining/offlining
> + * code requires applicable ranges to be page-aligned, for example, to
> + * set the migratetypes properly.
> + *
> + * TODO: Although we have a check here to make sure that vmemmap pages
> + * fully populate a PMD, it is not the right place to check for
> + * this. A much better solution involves improving vmemmap code
> + * to fallback to base pages when trying to populate vmemmap using
> + * altmap as an alternative source of memory, and we do not exactly
> + * populate a single PMD.
> + */
> + return memmap_on_memory &&
> + IS_ENABLED(CONFIG_MHP_MEMMAP_ON_MEMORY) &&
> + size == memory_block_size_bytes() &&
> + IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
> + IS_ALIGNED(remaining_size, (pageblock_nr_pages << PAGE_SHIFT));

IS_ALIGNED(remaining_size, pageblock_nr_pages << PAGE_SHIFT);

LGTM, thanks!

(another pair of eyes certainly wouldn't hurt :) )

Reviewed-by: David Hildenbrand <david@redhat.com>

--
Thanks,

David / dhildenb

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