On 22.04.20 10:21, Michal Hocko wrote: > On Tue 21-04-20 15:06:20, David Hildenbrand wrote: >> On 21.04.20 14:52, Michal Hocko wrote: >>> On Tue 21-04-20 14:35:12, David Hildenbrand wrote: >>>> On 21.04.20 14:30, Michal Hocko wrote: >>>>> Sorry for the late reply >>>>> >>>>> On Thu 16-04-20 12:47:06, David Hildenbrand wrote: >>>>>> A hotadded node/pgdat will span no pages at all, until memory is moved to >>>>>> the zone/node via move_pfn_range_to_zone() -> resize_pgdat_range - e.g., >>>>>> when onlining memory blocks. We don't have to initialize the >>>>>> node_start_pfn to the memory we are adding. >>>>> >>>>> You are right that the node is empty at this phase but that is already >>>>> reflected by zero present pages (hmm, I do not see spanned pages to be >>>>> set 0 though). What I am missing here is why this is an improvement. The >>>>> new node is already visible here and I do not see why we hide the >>>>> information we already know. >>>> >>>> "information we already know" - no, not before we online the memory. >>> >>> Is this really the case? All add_memory_resource users operate on a >>> physical memory range. >> >> Having the first add_memory() to magically set node_start_pfn of a hotplugged >> node isn't dangerous, I think we agree on that. It's just completely >> unnecessary here and at least left me confused why this is needed at all- >> because the node start/end pfn is only really touched when >> onlining/offlining memory (when resizing the zone and the pgdat). > > I do not see any specific problem. It just feels odd to > ignore the start pfn when we have that information. I am little bit > worried that this might kick back. E.g. say we start using the memmaps > from the hotplugged memory then the initial part of the node will never> get online and we would have memmaps outside of the node span. I do not That's a general issue, which I pointed out as response to Oscars last series. This needs more thought and reworks, especially how node_start_pfn/node_spanned_pages are glued to memory onlining/offlining today. > see an immediate problem except for the feeling this is odd. I think it's inconsistent. E.g., start with memory-less/cpu-less node and don't online memory from the kernel immediately. Hotplug CPU. PGDAT initialized with node_start_pfn=0. Hotplug memory. -> node_start_pfn=0 until memory is actually onlined. Hotplug memory. PGDAT initialized with node_start_pfn=$VALUE. Hotplug CPU. -> node_start_pfn=$VALUE Hotplug memory. PGDAT initialized with node_start_pfn=$VALUE. Hotplug CPU. Hotunplug memory. -> node_start_pfn=$VALUE, although there is no memory anymore. Hotplug memory 1. PGDAT initialized with node_start_pfn=$VALUE. Hotplug memory 2. Hotunplug memory 2. -> node_start_pfn=$VALUE1 instead of $VALUE2. Again, because node_start_pfn has absolutely no meaning until memory is actually onlined - today. > > That being said I will shut up now and leave it alone. Is that a nack? Thanks for having a look! -- Thanks, David / dhildenb
