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
