As part of a world upgrade, I had some pretty large (build time size) packages to upgrade: chromium, libreoffice, torbrowser, palemoon, qtwebengine, qtwebkit and a couple others. emerge chose to parallelize builds of (all) those aforementioned packages, causing my double-digit GB (must've been around 20 GB free) /var/tmp to run out of space, breaking ALL those builds and necessitating significant time and some coddling to get those built properly. I propose two possible / one building on the other solutions: a) there is a maximum of one parallel build started per free GB of /var/tmp/portage space. In addition, there's a way for an ebuild to specify larger build space requirements (GB granularity would be fine IMO) which would be similarly honored. Those could take the place of per-package pre-build-script size checks as are done by some packages now. b) similar to the time estimates used by genlop, max build directory sizes are tracked / logged some place and those (of previous versions) are used as a guesstimate, with some safety factor (x2, x1.5 or so). Falling back to something like (a) when there's no data from previous builds available.
