> I thought the plan was to migrate to per-user-tmp anyway, somewhere in $HOME, for apps that use a lot of tmp like DVD rippers this would be a good idea anyway.
Per-user directory would not get cleaned on reboot. Using per-user temporary directory may be a bad thing for users with NFS /home, they would prefer using local tmp if it is. Also a common /tmp for all users still needed for file exchange on a multiuser servers. And finally, why would DVD soft used something-in-HOME, if they can use /tmp which is there exactly for those things. ;)
Why put /tmp on tmpfs? Having /var/tmp/portage on tmpfs does not force you to put /tmp there. And it's really hard to find an application that becomes faster just because of /tmp on tmpfs. Even for portage it's not that obvious.
> Compiles on tmpfs are faster, factor is 1.8 to 2 in my tests
Hm... My simple test shows that tmpfs is just about 1-2% faster.
Here's the script to resemble a basic package build:
mount tmpfs or ext3 to /mnt/test, then
$ cd /mnt/test
$ wget http://curl.haxx.se/download/curl-7.26.0.tar.bz2
$ export CFLAGS='-O2 -g -pipe' CXXFLAGS='-O2 -g -pipe'
$ time sh -c 'tar xf curl-7.26.0.tar.bz2 && cd curl-7.26.0 && ./configure && make install DESTDIR=/mnt/test/root && cd ../root && tar czf ../curl-package.tar.gz * && cd .. && rm -rf curl-7.26.0 root'
real 70.983s user 48.685s sys 26.527s
real 70.635s user 48.390s sys 26.694s
real 70.701s user 48.203s sys 26.929s
real 70.867s user 48.636s sys 27.090s
real 70.744s user 48.297s sys 27.082s
real 71.690s user 48.401s sys 27.498s
real 71.614s user 48.340s sys 27.869s
real 71.531s user 48.836s sys 27.520s
real 71.479s user 48.306s sys 27.469s
real 71.635s user 48.540s sys 27.496s