Supporting LZ4 as initramfs compressor

[Dimitri John Ledkov]

On Tue, 15 Oct 2019 at 11:13, Dimitri John Ledkov <xnox at ubuntu.com> wrote:
>
> 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
>

The Cking recent lz4 measurements tests are documented in the
description of https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1840934

-- 
Regards,

Dimitri.