linux-ext4 - Re: Question about ext4 testing: need to produce a high depth extent tree to verify mapping code

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Date:   Fri, 5 Jul 2019 10:39:06 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     James Bottomley <James.Bottomley@...senpartnership.com>
Cc:     Theodore Ts'o <tytso@....edu>, linux-ext4@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        Parisc List <linux-parisc@...r.kernel.org>
Subject: Re: Question about ext4 testing: need to produce a high depth extent
 tree to verify mapping code

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.