On 08.08.2018 09:38, Oscar Salvador wrote: > On Tue, Aug 07, 2018 at 06:13:45PM -0400, Jerome Glisse wrote: >>> And since we know for sure that memhotplug-code cannot call it with ZONE_DEVICE, >>> I think this can be done easily. >> >> This might change down road but for now this is correct. They are >> talks to enumerate device memory through standard platform mechanisms >> and thus the kernel might see new types of resources down the road and >> maybe we will want to hotplug them directly from regular hotplug path >> as ZONE_DEVICE (lot of hypothetical at this point ;)). > > Well, I think that if that happens this whole thing will become > much easier, since we will not have several paths for doing the same thing. > > Another thing that I realized is that while we want to move all operation-pages > from remove_memory() path to offline_pages(), this can get tricky. > > Unless I am missing something, the devices from HMM and devm are not being registered > against "memory_subsys" struct, and so, they never get to call memory_subsys_offline() > and so offline_pages(). > > Which means that we would have to call __remove_zone() from those paths. > But this alone will not work. I mean, they move it to the zone ("replacing online/offlining code"), so they should take of removing it again. > > find_smallest/biggest_section_pfn are two functions that are being called from > > shrink_pgdat_span > and > shrink_zone_span > > to adjust zone_first_pfn/node_first_pfn and the spanned pages. > > Currently, find_smallest/biggest_section_pfn checks for the secion to be valid, > and this is fine since we are removing those sections from the remove_memory path. > > But if we want to move __remove_zone() to offline_pages(), we have to use > online_section() instead of valid_section(). > > This is all fine from offline_pages because the sections get offlined in: > > __offline_pages > offline_isolated_pages > offline_isolated_pages_cb > __offline_isolated_pages > offline_mem_sections > > > But this does not happen in HMM/devm path. > > I am pretty sure this is a dumb question, but why HMM/devm path > do not call online_pages/offline_pages? > > Thanks > -- Thanks, David / dhildenb