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SubjectRe: [RFC PATCH v2 3/4] mm,memory_hotplug: Add mhp_supports_memmap_on_memory
On Wed 25-11-20 12:20:47, Oscar Salvador wrote:
> mhp_supports_memmap_on_memory is meant to be used by the caller prior
> to hot-adding memory in order to figure out whether it can enable
> Enabling MHP_MEMMAP_ON_MEMORY requires:
> - architecture support for altmap
> - hot-added range spans a single memory block

It should also require a tunable (kernel parameter for now but maybe we
will need a more fine grained control later) to enable this explicitly.
Earlier discussions have pointed out that allocating vmemmap from each
section can lead to a sparse memory unsuitable for very large pages.
So I believe this should be an opt in.

Also is there any reason why this cannot be a preparatory patch for the
actual implementation? It would look more natural that way to me.

Michal Hocko

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