linux-ext4 - e4defrag seems too optimistic

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Message-ID: <YIpFK3or2Creo1qg@vapier>
Date:   Thu, 29 Apr 2021 01:33:38 -0400
From:   Mike Frysinger <vapier@...too.org>
To:     linux-ext4@...r.kernel.org
Subject: e4defrag seems too optimistic

i started running e4defrag out of curiosity on some large files that i'm
archiving long term.  its results seem exceedingly optimistic and i have
a hard time agreeing with it.  am i pessimistic ?

for example, i have a ~4GB archive:
$ e4defrag -c ./foo.tar.xz
<File>                                         now/best       size/ext
./foo.tar.xz
                                             39442/2             93 KB

 Total/best extents				39442/2
 Average size per extent			93 KB
 Fragmentation score				34
 [0-30 no problem: 31-55 a little bit fragmented: 56- needs defrag]
 This file (./foo.tar.xz) does not need defragmentation.
 Done.

i have a real hard time seeing this file as barely "a little bit fragmented".
shouldn't the fragmentation score be higher ?

as a measure of "how fragmented is it really", if i copy the file and then
delete the original, there's a noticeable delay before `rm` finishes.
-mike