> > > > > 2) if memmap_on_memory is on, and hotplug capacity (node1) is > > zone_movable - then each memory block (256MB) should appear > > as 252MB (-4MB of 64-byte page structs). For 256GB (my system) > > I should see a total of 252GB of onlined memory (-4GB of page struct) > > In memory_block_online(), we have: > > /* > * Account once onlining succeeded. If the zone was unpopulated, it is > * now already properly populated. > */ > if (nr_vmemmap_pages) > adjust_present_page_count(pfn_to_page(start_pfn), mem->group, > nr_vmemmap_pages); > > So we'd add the vmemmap pages to > * zone->present_pages > * zone->zone_pgdat->node_present_pages > > (mhp_init_memmap_on_memory() moved the vmemmap pages to ZONE_MOVABLE) > > However, we don't add them to > * zone->managed_pages > * totalram pages > > /proc/zoneinfo would show them as present but not managed. > /proc/meminfo would not include them in MemTotal > > We could adjust the latter two, if there is a problem. > (just needs some adjust_managed_page_count() calls) > > So yes, staring at MemTotal, you should see an increase by 252 MiB right now. > > > > > 2a) when dropping these memory blocks, I should see node0 memory use > > stay the same - since it was vmemmap usage. > > Yes. > > > > > I will double check that this isn't working as expected, and i'll double > > check for a build option as well. > > > > stupid question - it sorta seems like you'd want this as the default > > setting for driver-managed hotplug memory blocks, but I suppose for > > very small blocks there's problems (as described in the docs). > > The issue is that it is per-memblock. So you'll never have 1 GiB ranges > of consecutive usable memory (e.g., 1 GiB hugetlb page). Regardless of ZONE_MOVABLE or ZONE_NORMAL, right? Thanks, Yang > > > > > :thinking: - is it silly to suggest maybe a per-driver memmap_on_memory > > setting rather than just a global setting? For CXL capacity, this seems > > like a no-brainer since blocks can't be smaller than 256MB (per spec). > > I thought we had that? See MHP_MEMMAP_ON_MEMORY set by dax/kmem. > > IIRC, the global toggle must be enabled for the driver option to be considered. > > -- > Cheers, > > David / dhildenb >
