502 Error when viewing Files page

ZenDesk issue: https://gitlab.zendesk.com/agent/tickets/25482

Today we upgraded to 8.8.2

Since the upgrade one of our repositories are giving a 502 Whoops, “GitLab is taking too much time to respond” when trying to view the “Files”

The said repo has 1258 files. Although I doubt this is the issue, since another repo with 5k files is fine.

I noticed a core pegged to 100% with ruby process.

The machine running Gitlab is a 2 core, 4G machine

Attached are two traces using perf: "Hit the URL, then took a perf for +-10sec then waited a bit and did the 2nd perf."

perf.report.0 perf.report.1

perf report suggests this is an issue with Nokogiri. Customer attempted to disable syntax highlighting to no avail. Could be an issue with Markdown, possibly with rendering of titles?

/cc: @MrChrisW, @balameb