Interesting observation: If I first switch from the X11 display to the console
display (with Alt-F2), and then enter "echo mem >/sys/power/state" on the
console, above described crashes upon S3 resume do not occur, and I do not see
the "[TTM] Buffer eviction failed" in the kernel log, neither with
vm_update_mode=0, nor with vm_update_mode=3.

Switching back to the X11 display after a successful S3 resume to the console
also works fine.

What could be the relevant difference here?