Just in case you found Howard Mark's last editorial piece on market risk to be of value, there are many more editorials he's written at his company website going back over ten years. I have read a few of these past editorials, and find them all to be very illuminating.

For those who may be interested, the link to these editorials, covering a variety of different market subjects is available here. They are broken out by year published:

http://www.oaktreecapital.com/memo.aspx