On Wed, Dec 02, 2020 at 10:36:54AM +0100, David Hildenbrand wrote: > Instead of adding these arch callbacks, what about a config option > > ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE > > that gets selected by the archs with CONFIG_SPARSEMEM_VMEMMAP ? > > The mhp_supports_memmap_on_memory() becomes even more trivial. I think that would not be enough. E.g: s390x supports CONFIG_SPARSEMEM_VMEMMAP but it does not support altmap (and maybe other arches I did not check too). That is why I was careful in choosing the ones that a) supports CONFIG_SPARSEMEM_VMEMMAP and b) support altmap > > Note that mhp_memmap_on_memory kernel boot option will be added in > > a coming patch. > > I think it makes sense to > > a) separate off the arch changes into separate patches, clarifying why > it can be used. Move this patches to the end of the series. > > b) Squashing the remainings into patch #2 Ok, I can do that. > > +/* > > + * We want memmap (struct page array) to be self contained. > > + * To do so, we will use the beginning of the hot-added range to build > > + * the page tables for the memmap array that describes the entire range. > > + * Only selected architectures support it with SPARSE_VMEMMAP. > > You might want to add how the caller can calculate the necessary size > and that that this calculated piece of memory to be added will be > accessed before onlining these pages. This is e.g., relevant if > virtio-mem, the hyper-v balloon, or xen balloon would want to use this > mechanism. Also, it's somewhat incompatible with standby memory where > memory cannot be accessed prior to onlining. So pointing that access out > might be valuable. Sure, I will be more verbose. > You can simplify to > > return arch_support_memmap_on_memory() && > IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) && > size == memory_block_size_bytes(); Yeah, thanks ;-) -- Oscar Salvador SUSE L3
