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 > MHP_MEMMAP_ON_MEMORY or not. > > Enabling MHP_MEMMAP_ON_MEMORY requires: > > - CONFIG_SPARSEMEM_VMEMMAP > - 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 SUSE Labs
