Re: Reduce loading time (size) of init program (systemd)

In his talk *Linux kernel fastboot on the way* at this years Linux
Plumbers Conference [1][2], Feng Tang (CCed) has the notes below on
the slide for userspace/systemd.

• Systemd is ~1.5MB - the loading time for emmc is 100ms> • Can we use a small lightweight “init” program, which starts
  target programs in parallel and readahead to preload libraries
  and executables?

Are you already aware of these issues? If yes, have you ideas or
suggestions how to solve this? Maybe something to discuss at this
weeks All System Go! 2019.

Chiming in here

The benefits of doing that often don't outweigh the cost. Readahead is *difficult* and very much impossible to get right for a generic situation, so in many cases it has stopped being used. The only place e.g. ClearLinux uses it now is for targeted use cases where it makes sense (in our case, the desktop, because GNOME is ... monstrous). For typical cloud and bare metal situations and even VM instances, readahead doesn't appear to be useful at all.

Despite loading time for eMMC being 100ms,  I've not seen the actual loading time of systemd be an issue. The worst thing at boot that can happen is that some process starts writing a lot (journal rotating, for instance), and is far more detrimental to boot time from my experience.

I like Feng's slides, but, it's not the first time that things were proposed that didn't pan out as much as we thought it did.

Auke