[Bug 1959971] Re: increase /boot partition size

[Łukasz Zemczak]

@kfocus Thank you for the detailed assessment! For 20.04 (at least for
20.04.4) we will only bump the partition sizes slightly, as mentioned in
the current description (and in the current SRU). We need to thread
carefully as it's a point-release of an already released series. As for
22.04, we are certainly open to discussion and your findings will be
very helpful to make the best decision.

Let's see how it goes.

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https://bugs.launchpad.net/bugs/1959971

Title:
  increase /boot partition size

Status in partman-auto package in Ubuntu:
  Triaged
Status in ubiquity package in Ubuntu:
  Confirmed
Status in partman-auto source package in Focal:
  Fix Committed
Status in ubiquity source package in Focal:
  Fix Committed
Status in partman-auto source package in Jammy:
  Triaged
Status in ubiquity source package in Jammy:
  Confirmed

Bug description:
  [Impact]
  All new installs of 20.04.

  [Test case]
  1) Install Ubuntu 20.04 with encryption (this'll create a separate /boot partition) on a system
  2) Validate that the size of the /boot partition is greater than or equal to 768MB; should be somewhere between 768MB and 1536GB.

  [Regression potential]This may adversely affect installs on tiny disks, by taking up more space for the /boot partition than was previously taken, at the cost of / or /home. As such, failures to install due to insufficient space on a partition, or failure to partition a disk that was previously working should be investigated as possible regressions.
  This is a corner case in general since there is no requirement to allocate a separate partition for /boot in the default configuration, and if you are using a non-default configuration where /boot must be a separate partition, you probably also don't have a disk so small that an additional 256MB of disk usage is a problem.

  ---
  The kernel in Jammy is a bit larger than the one in Focal and our previous /boot partition size calculation (LP: #1716999) likely didn't take into account adding modules like nvidia to the initramfs. Subsequently, we need to revisit the size calculations for Focal.

  I'm utilizing cryptsetup and nvidia modules and have a 164M initrd
  when using lz4 (the default in Focal) compression. Using the same
  formula we previously did we end up with this:

  2* (3*11 + 4*164 + 11) = 1400

  So modifying the maximum size to 1536 seems reasonable, the current
  minimum is 512 which is actually a bit too small for an initrd with
  less modules e.g.:

  2* (3*11 + 4*62 + 11) = 584

  So the minimum should also be increased to 768.

  The default compression level for Jammy is currently being discussed
  and until that is decided we shouldn't make changes to partman-auto
  for Jammy.

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