Something is broken in repack

Using this config:
[pack]
        threads = 4
        deltacachesize = 256M
        deltacachelimit = 0

And the 330MB gcc pack for input
 git repack -a -d -f  --depth=250 --window=250

complete seconds RAM 10% 47 1GB 20% 29 1Gb 30% 24 1Gb 40% 18 1GB 50% 110 1.2GB 60% 85 1.4GB 70% 195 1.5GB 80% 186 2.5GB 90% 489 3.8GB 95% 800 4.8GB I killed it because it started swapping

The mmaps are only about 400MB in this case. At the end the git process had 4.4GB of physical RAM allocated.

Starting from a highly compressed pack greatly aggravates the problem. Starting with a 2GB pack of the same data my process size only grew to 3GB with 2GB of mmaps.