Bug#1076561:

[Michael Neilly]

FWIW - I found that editing /etc/initramfs-tools/initramfs.conf and setting 
COMPRESS=lzma and COMPRESSLEVEL=9 was enough to get initrd to fit in my /boot. 
Using lzma instead of zstd for this particular release changed the size of the 
ram disk from 229,092,670 bytes to 86,150,862 bytes. Of course it takes longer 
to create.