On 13.04.2018 15:40, Michal Hocko wrote: > On Fri 13-04-18 15:16:26, David Hildenbrand wrote: >> online_pages()/offline_pages() theoretically allows us to work on >> sub-section sizes. This is especially relevant in the context of >> virtualization. It e.g. allows us to add/remove memory to Linux in a VM in >> 4MB chunks. > > Well, theoretically possible but this would require a lot of auditing > because the hotplug and per section assumption is quite a spread one.
Indeed. But besides changing section sizes / size of memory blocks this seems to be the only way to do it. (btw, I think Windows allows to add 1MB chunks - e.g. 1MB DIMMs) But as these pages "belong to nobody" nobody (besides kdump) should dare to access the content, although the section is online. > >> While the whole section is marked as online/offline, we have to know >> the state of each page. E.g. to not read memory that is not online >> during kexec() or to properly mark a section as offline as soon as all >> contained pages are offline. > > But you cannot use a page flag for that, I am afraid. Page flags are > extremely scarce resource. I haven't looked at the rest of the series > but _if_ we have a bit spare which I am not really sure about then you > should prove there are no other ways around this. Open for suggestions. We could remember per segment/memory block which parts are online/offline and use that to decide if a section can go offline. However: kdump will also have to (easily) know which pages are offline, so it can skip reading them. (see the other patch) > >> Signed-off-by: David Hildenbrand <da...@redhat.com> -- Thanks, David / dhildenb