ext4 and extremely slow filesystem traversal

[Peter Grandi]

>>>> It also has 0 reserved blocks.

>> That's usually a truly terrible setting (20% is a much better
>> value), but your filesystem is not very full anyhow.

> This filesystem has no file owned by root and won't have
> any. I thought in this case -m0 would be a good idea.

Why does it matter here that "no file owned by root"?

What has that got to do with the much greater difficulty to find
contiguous space the fuller the filetree is?