How to increase diffs limits

Gitlab version: Gitlab-ce 9.4.6
Hi we have faced the case in which diffs does not showing with error: This source diff could not be displayed because it is too large. You can view the blob instead.

I’ve found this issue: issue 30061

But here in 9.4.6 was not DIFF_SIZE_LIMIT or DIFF_HARD_LIMIT_LINES parameters in /opt/gitlab/embedded/service/gitlab-rails/app/models/commit.rb

there is a function:
def find_size_limit
if Feature.enabled?(‘gitlab_git_diff_size_limit_increase’)

So i’ve tried to find where can i enable this feature but i did not found it.

The only way i can propose is to switch it on on gitlab.rb using gitlab_rails[‘gitlab_git_diff_size_limit’] = enable

Can you please point me into the right direction about this problem?