Supporting LZ4 as initramfs compressor

[Dimitri John Ledkov]

On Wed, 5 Jun 2019 at 21:25, Dimitri John Ledkov <xnox at ubuntu.com> wrote:
>
> On Wed, 5 Jun 2019 at 19:59, Steve Langasek <steve.langasek at ubuntu.com> wrote:
> >
> > Hi Dimitri,
> >
> > One point here:
> >
> > On Wed, Jun 05, 2019 at 01:15:48PM +0100, Dimitri John Ledkov wrote:
> > > - lz4 size weight over gzip is marginal (14%) but imho worth the
> > > improved boot time & initrd creation time
> >
> > A 14% increase in initramfs size is NOT marginal.  Since there are (and will
> > always be) various scenarios which require a separate /boot partition, we
> > have over several cycles been contending with how to ensure a clean upgrade
> > as kernel+initramfs sizes increase over time and push up against the space
> > limits of the boot partitions that have historically been created.
> >
> > If you are making a change that increases the size of initramfses by 14%
> > across the board, you must also:
> >
> >  - update the ubuntu-release-upgrader code to take this into account so
> >    users don't run out of space in the middle of the upgrade
> >    - possibly in a way that is smart enough to know if a user is already
> >      configuring initramfs-tools to use a non-default compressor, to avoid
> >      false-positives
> >  - check that the minimum size requirements for /boot that are encoded in
> >    the installers are still adequate, or if they need updating (and if they
> >    need updating, update this back to 18.04)
> >  - document this issue in the release notes
>

ubuntu-release-upgrader is dynamically calculated, but I have now
proposed to bump/update the fallback guestimate.

did the calculation of new size requirements, and /boot sizes are
still well enough (up to 10 kernels)

release notes updated

-- 
Regards,

Dimitri.