TAU_TRACK_MEMORY_HEADROOM_HERE(3) on Linux
The text bcbfc6b7136f, as Debian 9 (Stretch), Debian 8 (Jessie), Debian 7 (Wheezy), Debian 6.0 (Squeeze), Debian 4.0 (Etch) shipped it. The page shows this text now.
Takes a sample of the amount of memory available at a given point.