Ubuntu 21.10 (Impish Indri) has reached end of life, so this bug will
not be fixed for that specific release.
** Changed in: initramfs-tools (Ubuntu Impish)
Status: New => Won't Fix
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https://bugs.launchpad.net/bugs/1932329
Title:
Support compressed kernel modules in initramfs-tools and kernel
Status in initramfs-tools package in Ubuntu:
Fix Released
Status in linux package in Ubuntu:
In Progress
Status in initramfs-tools source package in Focal:
New
Status in initramfs-tools source package in Impish:
Won't Fix
Status in initramfs-tools source package in Jammy:
Fix Released
Status in linux source package in Jammy:
In Progress
Bug description:
--- initramfs-tools
[Impact]
* Initramfs-tools already supports compressed kernel modules.
However, in focal and impish it does so inefficiently. It is always
better to have a compressed initramfs of uncommpressed kernel modules,
than a compressed initrd of compressed kernel modules. Thus when
kernel module compression is turned on, it is prudent for initramfs-
tools to pre-uncompress kernel modules when building initramfs.
[Test Plan]
* Compress all kernel modules with xz for a current kernel, check
that all of them have .ko.xz extension and no .ko ones available
* Rerun depmod
* Update initramfs with update-initramfs -u
* lsinitramfs contents and check that all kernel modules are present,
and are uncompressed (.ko extension)
[Where problems could occur]
* This optimization for compressed kernel modules will make initramfs
build time longer (due to decompression) whilst improving bootspeed
(overall smaller size of the initrd).
[Other Info]
* Original bug report re kernel feature
--- linux
Symbol: MODULE_COMPRESS_ZSTD [=n]
Type : bool
= Impacts to measure and observe =
== Disk space ==
* Inspect linux-modules-* and linux-modules-extra* deb package
Installed-Size and Download-Size changes, i.e.
$ apt show linux-modules-5.8.0-53-generic linux-modules-
extra-5.8.0-53-generic | grep -e Package: -e Size:
Package: linux-modules-5.8.0-53-generic
Installed-Size: 81.5 MB
Download-Size: 15.5 MB
Package: linux-modules-extra-5.8.0-53-generic
Installed-Size: 215 MB
Download-Size: 41.5 MB
In theory, there should not be a significant change in the Download-
size. It is desired that there is a significant reduction in
Installed-Size. Modules take up about 300MB and normally one has upto
three kernel version installed, resulting in about of 1GB of disk
space that one constantly pays for.
== Boot Speed ==
In theory, boot speed may either improve or regress. It depends if
disk IO is slower than decompression speed, meaning loading compressed
modules is faster.
Also one has to observe the changes in the initrd size. zstd(zstd)
compression may result in slight growth, which shouldn't impact boot
speed too much.
= Outcomes =
If installed size savings can be achieved without regressing bootspeed
we should enable CONFIG_MODULE_COMPRESS_ZSTD=y by default.
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