On Sat, 2023-07-08 at 01:25 +0100, Dimitri John Ledkov wrote: > On Sat, 8 Jul 2023 at 01:19, Benjamin Drung <bdr...@ubuntu.com> wrote: > > > > 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 > > > > Majority of our instances boot without initrd, and there too they > don't load most of the modules. > Creating xz -9 compressed archive of all modules, still pays the > penalty to decompress most of them, and then not modprobe them. > I was hoping to achieve a similar in spirit approach, but didn't quite > have the time to implement is: > > 1) change linux-modules and linux-firmware to ship .ko.zst > firmware.bin.zst compressed with zstd -19 at .deb build time > 2) this saves install size of the packages, with only slightly > increased download size > 3) modify initramfs-tools to include compressed files into a separate > initrd, which is not compressed (i.e. exclude .zst files from the > default main compressed cpio archive, and append them in the second > main cpio archive that is uncompressed) > 4) this should achieve quick initrd creation, which will be smaller in > size that current status, and will boot faster as it will only > decompress modules/firmware it actually needs at boot > > For experimentation locally, you can recompress .ko with zstd in place > in /lib/modules/; and rerun depmod. To then test initramfs-tools > changes that skip over .zst compressed files and add them as is in an > uncompressed appended cpio.
That is a very good idea. I created a draft for point 3 in [2]. It moves the compressed files into a separate directory and creates a separate cpio archive for that directory without compressing it: * AMD/Intel microcode cpio archive (on amd64) * main cpio archive (compressed) * compressed kernel modules / firmware (not compressed) Sadly this does not work (yet). cpio complains with "premature end of archive" when looking at it and the kernel fails to extract the last cpio part. I am heading to bed now leaving that bug for another day. [2] https://code.launchpad.net/~bdrung/ubuntu/+source/initramfs-tools/+git/initramfs-tools/+ref/ubuntu/compressed -- Benjamin Drung Debian & Ubuntu Developer -- ubuntu-devel mailing list ubuntu-devel@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-devel
