On Sun, Jul 09, 2023 at 04:28:42AM +0200, Heinrich Schuchardt wrote:
> > > Benjamin Drung <bdrung@ubuntu.com> schrieb am Sa., 8. Juli 2023, 02:19:
> > > > Hi all,
> > > > a year ago we changed the default compression and level for the
> > > > initramfs to zstd -1. This fixed the very slow creation times on
> > > > development boards (see bug #1958148), but that leads to bigger
> > > > initramfs sizes that triggered other bugs (like bug #1842320).
> > > > Big initramfs sizes can also fill up small sized /boot partitions easily
> > > > (grooming the 850 initramfs-tools bugs revealed several such reports).
> > > > Using xz -9 would give very good compression, but it takes very long
> > > > (especially on slow development boards) and a lot of memory (good luck
> > > > on Raspberry Pis with small memory like Pi Zeros).
> > > > I propose following approach to address the drawback: Create cpio
> > > > archives (compressed with xz -9) for the kernel modules and firmware
> > > > files when building the kernel/firmware Debian package. Then ship those
> > > > cpio archives in the package (or in a separate binary package). Then the
> > > > CPU load it put on the builders. The cpio archives would contain the
> > > > modules for MODULES=most.
> > > > mkinitramfs will then look for those cpio archives and uses those in
> > > > case they are present. Such a initramfs would look like this:
> > > > * AMD/Intel microcode cpio archive (on amd64)
> > > > * main cpio archive compressed with zstd -1
> > > > * kernel modules from the Debian package compressed with xz -9
> > > > * firmware files from the Debian package compressed with xz -9
> > > > After working on initramfs-tools as part my day job, my fingers were
> > > > itching and I had to create a quick and dirty draft in my free night
> > > > time. You can find the result of the last two hours in [1]. This draft
> > > > has a mkinitramfs-kernel script that creates a cpio archive containing
> > > > the kernel modules and firmware (that needs to be split later on).
> > > > The lunar test result on my AMD Ryzen 7 5700G look promising: Building
> > > > 6.2.0-24-generic-modules-most.cpio.xz takes around 90 seconds and is
> > > > 54.9 MiB in size. Creating the initramfs speeds up from around 8.7
> > > > seconds to 3.5 seconds (saves 60 %). The size reduces from 133.1 MiB to
> > > > 80.7 MiB (saves 39.4 %). So the boot needs 52.4 MiB less, but
> > > > /lib/modules need 54.9 MiB for the cpio archive.
> > > > The drawback is that building the kernel would take longer, the package
> > > > takes more space on the archive and mirrors, and downloading them could
> > > > take longer on slow connections.
> > > > Implementing my proposal would be relative easy for initramfs-tools, but
> > > > would mean some work for the kernel team.
> > > > What do you think?
> Will the user still be able to add further modules and will machine specific
> configuration files (e.g. for booting from iSCSI) still be included into the
> initrd?
I think a robust implementation of this on the initramfs-tools side looks
like:
- identify all the contents that belong in the initramfs
- among those contents, find all zstd-compressed files, if any, and store
them in an uncompressed initramfs
- put the rest of the contents in a compressed initramfs
This would be compatible with kernel packages whether they are changed to
ship zstd-compressed modules or not and allow for a smooth transition.
--
Steve Langasek Give me a lever long enough and a Free OS
Debian Developer to set it on, and I can move the world.
Ubuntu Developer https://www.debian.org/
slangasek@ubuntu.com vorlon@debian.org
