linux-stable/branches takes 2 minutes

Summary

When working on a linux-stable tree, browsing the branches tab takes 2 minutes to render (2 minutes on a fast server).

Steps to reproduce

• clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
• click on "XYZ branches"
• wait ...

On gitlab.com the problem is reproduced here : (error 502 in the end) https://gitlab.com/ebenard/linux-stable/branches

Expected behavior

faster answer

Relevant logs and/or screenshots

on gitlab.com : on my own server :