Hi Matthew, Consider the following excerpt from the Xarray documentation on multi-index entries, summarizing the [2^N, 2^(N+1) - 1] alignment requirement for utilizing multi-index entries [1]: "The current implementation only allows tying ranges which are aligned powers of two together; eg indices 64-127 may be tied together, but 2-6 may not be. This may save substantial quantities of memory; for example tying 512 entries together will save over 4kB." Won't we still use multi-index entries for power-of-two ranges that are aligned for the size of the range? That is, the range [i, j] satisfies: (A): j - i = 2^k for some k and i % 2^k == 0 . This is more permissive than [2^N, 2^(N+1) - 1] . I'm basing this assumption (calling it this as I'm not 100% certain yet) off of the following: (1) Counting the number of kmem_cache_alloc_lru() calls using ranges satisfying (A) whilst varying the starting position. (2) Walking through xa_store_range(). The call to xas_set_range() [2] sets the final xa_shift S that corresponds to the range we want to cover. When calling xas_store() [3], inside of which is a call to xas_create() [4], the shift of the lowest-level node [5] we allocate is no smaller than S - XA_CHUNK_SHIFT + 1, i.e. the entry will still cover multiple entries so long as S is large enough (though we still might need multiple entries to do this). This will happen despite the alignment of things, based of what happens in xas_store_range(). Let me know if I'm misinterpreting something. Thanks, Chris. [1] https://docs.kernel.org/core-api/xarray.html#multi-index-entries [2] https://elixir.bootlin.com/linux/latest/source/lib/xarray.c#L1740 [3] https://elixir.bootlin.com/linux/latest/source/lib/xarray.c#L1741 [4] https://elixir.bootlin.com/linux/latest/source/lib/xarray.c#L789 [5] https://elixir.bootlin.com/linux/latest/source/lib/xarray.c#L679
