[mindjiver]

At a previous job I migrated a quite large code base to git. IIRC it was at least 500k files and a couple of 10MLOCs. We had the same "scaling" issues Facebook mentioned here when trying to place all of this inside one repository. So we ended up going with submodules for this. Another idea was to perhaps enable re-use of repositories and/or disconnect old legacy code this way.

We did took a quick look at Mercurial but since lots of the upstream tools we used was using Git (linux, uboot, yocto, etc) it was an obvious choice. I seem to recall there being two hg extension that where of interest at the time (2010-ish), one to add inotify support and another to store large files outside the repository (hg-largefiles?).

Seem like Facebook's approach to the lstat(2) issue with watchman [1] is to use inotify on Linux. This has been discussed a couple of times for git as well but nothing has come of it so far [2].

[1] https://github.com/facebook/watchman [2] http://git.661346.n2.nabble.com/inotify-to-minimize-stat-cal...