On Fri, Jul 05, 2019 at 09:25:48AM -0700, James Bottomley wrote:

Now the problem: I'd like to do some testing with high depth extent
trees to make sure I got this right, but the files we load at boot are
~20MB in size and I'm having a hard time fragmenting the filesystem
enough to produce a reasonable extent (I've basically only got to a two
level tree with two entries at the top).  Is there an easy way of
producing a high depth extent tree for a 20MB file?

Create a series of 4kB files numbered sequentially, each 4kB in size
until you fill the partition.  Delete the even numbered ones.  Create a
20MB file.