On Tue, 22 Sep 2020, Matthew Wilcox wrote: > On Mon, Sep 21, 2020 at 12:20:42PM -0400, Mikulas Patocka wrote: > > The same for directories - NVFS hashes the file name and uses radix-tree > > to locate a directory page where the directory entry is located. XFS > > b+trees would result in much more accesses than the radix-tree. > > What? Radix trees behave _horribly_ badly when indexed by a hash. > If you have a 64-bit hash and use 8 bits per level of the tree, you have > to traverse 8 pointers to get to your destination. You might as well > use a linked list! In NVFS, radix trees are cut off - they have only as much internal levels, as is needed to disambiguate the directory entries. Read this document: http://people.redhat.com/~mpatocka/nvfs/INTERNALS the section "DIRECTORIES". Perhaps, I should call it differently than "radix-trees", but I don't really know what is the official name for this data structure. Mikulas
