On Thu, Aug 01, 2019 at 10:17:23AM +0200, David Hildenbrand wrote: > I am not yet sure about two things: > > > 1. Checking uninitialized pages for PageVmemmap() when onlining. I > consider this very bad. > > I wonder if it would be better to remember for each memory block the pfn > offset, which will be used when onlining/offlining. > > I have some patches that convert online_pages() to > __online_memory_block(struct memory block *mem) - which fits perfect to > the current user. So taking the offset and processing only these pages > when onlining would be easy. To do the same for offline_pages(), we > first have to rework memtrace code. But when offlining, all memmaps have > already been initialized. This is true, I did not really like that either, but was one of the things I came up. I already have some ideas how to avoid checking the page, I will work on it. > 2. Setting the Vmemmap pages to the zone of the online type. This would > mean we would have unmovable data on pages marked to belong to the > movable zone. I would suggest to always set them to the NORMAL zone when > onlining - and inititalize the vmemmap of the vmemmap pages directly > during add_memory() instead. IMHO, having vmemmap pages in ZONE_MOVABLE do not matter that match. They are not counted as managed_pages, and they are not show-stopper for moving all the other data around (migrate), they are just skipped. Conceptually, they are not pages we can deal with. I thought they should lay wherever the range lays. Having said that, I do not oppose to place them in ZONE_NORMAL, as they might fit there better under the theory that ZONE_NORMAL have memory that might not be movable/migratable. As for initializing them in add_memory(), we cannot do that. First problem is that we first need sparse_mem_map_populate to create the mapping, and to take the pages from our altmap. Then, we can access and initialize those pages. So we cannot do that in add_memory() because that happens before. And I really think that it fits much better in __add_pages than in add_memory. Given said that, I would appreciate some comments in patches#3 and patches#4, specially patch#4. So I would like to collect some feedback in those before sending a new version. Thanks David -- Oscar Salvador SUSE L3
