On Thu 21-03-19 13:38:20, Anshuman Khandual wrote: > Memory hot remove uses get_nid_for_pfn() while tearing down linked sysfs > entries between memory block and node. It first checks pfn validity with > pfn_valid_within() before fetching nid. With CONFIG_HOLES_IN_ZONE config > (arm64 has this enabled) pfn_valid_within() calls pfn_valid(). > > pfn_valid() is an arch implementation on arm64 (CONFIG_HAVE_ARCH_PFN_VALID) > which scans all mapped memblock regions with memblock_is_map_memory(). This > creates a problem in memory hot remove path which has already removed given > memory range from memory block with memblock_[remove|free] before arriving > at unregister_mem_sect_under_nodes(). Could you be more specific on what is the actual problem please? It would be also helpful to mention when is the memblock[remove|free] called actually. > During runtime memory hot remove get_nid_for_pfn() needs to validate that > given pfn has a struct page mapping so that it can fetch required nid. This > can be achieved just by looking into it's section mapping information. This > adds a new helper pfn_section_valid() for this purpose. Its same as generic > pfn_valid(). I have to say I do not like this. Having pfn_section_valid != pfn_valid_within is just confusing as hell. pfn_valid_within should return true whenever a struct page exists and it is sensible (same like pfn_valid). So it seems that this is something to be solved on that arch specific side of pfn_valid. -- Michal Hocko SUSE Labs
