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It is designed to be preserved and restored over Kexec > Handover (KHO), and targets only 64-bit platforms. It can store 8-byte > aligned pointers. It can also store integers between 0 and LONG_MAX. It > supports sparse indices, though it performs best with densely clustered > indices. That is a bit of an understatement, it looks like worst case cost is 4k per entry. I would expect better efficiency than this if we are serious about supporting sparsity.. I think you need to encode the start pos within the entries in some way so worst case cost is bounded to more like 16/24 byte per entry. For instance if the page was broken up into an array of structs like struct entries_block { u64 flags:1; u64 num_entries:13 u64 pos_increment:50; u64 entries[]; // contiguous pos }; And if a high 64 bit pos can't be represented with pos_increment then you'd have flags = X and entries[0] == pos instead. Jason