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Date:   Tue, 22 Sep 2020 13:28:19 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Mikulas Patocka <mpatocka@redhat.com>
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Subject: Re: NVFS XFS metadata (was: [PATCH] pmem: export the symbols
 __copy_user_flushcache and __copy_from_user_flushcache)
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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!