Regarding the “summary” line (the 50 in your formula), the Linux kernel documentation has this to say:
For these reasons, the "summary" must be no more than 70-75
characters, and it must describe both what the patch changes, as well
as why the patch might be necessary. It is challenging to be both
succinct and descriptive, but that is what a well-written summary
should do.
That said, it seems like kernel maintainers do indeed try to keep things around 50. Here’s a histogram of the lengths of the summary lines in the git log for the kernel:
There is a smattering of commits that have summary lines that are longer (some much longer) than this plot can hold without making the interesting part look like one single line. (There’s probably some fancy statistical technique for incorporating that data here but oh well… 🙂
If you want to see the raw lengths:
cd /path/to/repo
git shortlog | grep -e '^ ' | sed 's/[[:space:]]\+\(.*\)$/\1/' | awk '{print length($0)}'
or a text-based histogram:
cd /path/to/repo
git shortlog | grep -e '^ ' | sed 's/[[:space:]]\+\(.*\)$/\1/' | awk '{lens[length($0)]++;} END {for (len in lens) print len, lens[len] }' | sort -n