dracut: slim down initramfs, speed up generation

stapelberg commented 5 years ago

With #1 fixed, we have a lot more Linux kernel modules. The images we produce cannot use dracut’s hostonly mode (individual users can, though). It would be nice to exclude e.g. SCSI modules (largest in terms of file size) from the generic dracut initrd, as it is very unlikely that someone needs to boot the distri live image from a SCSI storage system (they can still install onto it).

Here are a couple of avenues to investigate:

[ ] omit scsi modules. Unfortunately, it doesn’t seem as simple as passing --omit-drivers ".*/scsi/.*", even though that should work.
[ ] omit file systems: With regards to file systems, we can specify e.g. filesystems+=9p in /etc/dracut.conf.d/fs.conf so that all others are excluded. 9p is small enough, and we can’t use ext4, as that’s already built-in (not a loadable module).
[ ] we should look into which compression algorithm/settings to use. Specifying --no-compress removes 30s from 90s dracut time, so perhaps there is a more CPU-efficient compression scheme.
- [ ] try packaging pigz, which dracut should pick up
[ ] we should look into using --nostrip. In my evaluation, the size of the initrd was unchanged, but not stripping files removes 20s from 60s dracut time.
[ ] dracut-install seems to call cp(1) for each file (!) it copies, which can be quite a number when copying kernel modules. Running cp(1) is especially expensive on distri thanks to hermetic packages, where the correct binary needs to be located (iterating through $PATH), and running the binary means resolving the shared libraries, which is also pretty expensive.

stapelberg commented 4 years ago

This is obsolete with minitrd: https://michael.stapelberg.ch/posts/2020-01-21-initramfs-from-scratch-golang/

anatol commented 4 years ago

minimalistic initram would be beneficial for the community and people who does not plan to use distri os. Are there any plans to release minitrd as a standalone project that can be used with other distros?

stapelberg commented 4 years ago

No: https://michael.stapelberg.ch/posts/2020-01-21-initramfs-from-scratch-golang/#minitrd-outside-of-distri

distr1 / distri

dracut: slim down initramfs, speed up generation #22