On 23.11.18 13:42, Michal Hocko wrote: > On Fri 23-11-18 12:55:41, Oscar Salvador wrote: >> On Thu, Nov 22, 2018 at 10:21:24AM +0100, David Hildenbrand wrote: >>> 1. How are we going to present such memory to the system statistics? >>> >>> In my opinion, this vmemmap memory should >>> a) still account to total memory >>> b) show up as allocated >>> >>> So just like before. >> >> No, it does not show up under total memory and neither as allocated memory. >> This memory is not for use for anything but for creating the pagetables >> for the memmap array for the section/s. > > I haven't read through your patches yet but wanted to clarfify few > points here. > > This should essentially follow the bootmem allocated memory pattern. So > it is present and accounted to spanned pages but it is not managed. > >> It is not memory that the system can use. > > same as bootmem ;) Fair enough, just saying that it represents a change :) (but people also already complained if their VM has XGB but they don't see actual XGB as total memory e.g. due to the crash kernel size) > >> I also guess that if there is a strong opinion on this, we could create >> a counter, something like NR_VMEMMAP_PAGES, and show it under /proc/meminfo. > > Do we really have to? Isn't the number quite obvious from the size of > the hotpluged memory? At least the size of vmmaps cannot reliably calculated from "MemTotal" . But maybe based on something else. (there, it is indeed obvious) > >> >>> 2. Is this optional, in other words, can a device driver decide to not >>> to it like that? >> >> Right now, is a per arch setup. >> For example, x86_64/powerpc/arm64 will do it inconditionally. >> >> If we want to restrict this a per device-driver thing, I guess that we could >> allow to pass a flag to add_memory()->add_memory_resource(), and there >> unset MHP_MEMMAP_FROM_RANGE in case that flag is enabled. > > I believe we will need to make this opt-in. There are some usecases > which hotplug an expensive (per size) memory via hotplug and it would be > too wasteful to use it for struct pages. I haven't bothered to address > that with my previous patches because I just wanted to make the damn > thing work first. > Good point. -- Thanks, David / dhildenb
