On Sat, 8 Jul 2023, 02:49 Benjamin Drung, <bdr...@ubuntu.com> wrote: > 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. >
I had this before with lz4 and lzo compression and fixed this before in the kernel. It is likely a kernel bug mishandling mixed compression initrds. It will likely work if you.... Make compressed-files the third early initrd. Such that we have intel, AMD microcode early initrds, followed by compressed-files initrd, followed by compressed main initrd. > [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
