With 16G tmpfs mounted at /var/tmp/portage src_test fails, with 'while true;do sleep 60;df -m /var/tmp/portage/ >> /tmp/df-m-boost;done' i found it needs 23402 MB when using tmpfs. I do not know how much does it need with ext4. P.S. Building with tests enabled needs 4 hours, qlop -gH boost: boost: Thu May 24 21:37:47 2012: 3 hours, 58 minutes, 46 seconds
This has been removed in 1.51.0-r1 as the tests are completely pointless for Gentoo.