On Fri 13-04-18 16:01:43, David Hildenbrand wrote: > On 13.04.2018 15:44, Michal Hocko wrote: > > [If you choose to not CC the same set of people on all patches - which > > is sometimes a legit thing to do - then please cc them to the cover > > letter at least.] > > > > On Fri 13-04-18 15:16:24, David Hildenbrand wrote: > >> I am right now working on a paravirtualized memory device ("virtio-mem"). > >> These devices control a memory region and the amount of memory available > >> via it. Memory will not be indicated via ACPI and friends, the device > >> driver is responsible for it. > > > > How does this compare to other ballooning solutions? And why your driver > > cannot simply use the existing sections and maintain subsections on top? > > > > (further down in this mail is a small paragraph about that) Sorry, I just stopped right there and didn't even finsh to the end. Shame on me! I will do my homework and read it carefully (next week). [...] > "And why your driver cannot simply use the existing sections and > maintain subsections on top?" > > Can you elaborate how that is going to work? What I do as of now, is to > remember for each memory block (basically a section because I want to > make it as small as possible) which chunks ("subsections") are > online/offline. This works just fine. Is this what you are referring to? Well, basically yes. I meant to suggest you simply mark pages reserved and pull them out. You can reuse some parts of such a struct page for your metadata because we should simply ignore those. You still have to allocate memmap for the full section but 128MB sections have a nice effect that they fit into a single PMD for sparse-vmemmap. So you do not really need to touch mem sections, all you need is to keep your metadata on top. -- Michal Hocko SUSE Labs