On Sat, 2023-07-08 at 03:23 +0100, Dimitri John Ledkov wrote: > > > 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's not only the kernel. It is also cpio that complains. > 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. > It did. > > [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
