Improve compression ratio of SquashFS filesystem on the installation media.
Name: Bohdan Khomutskyi
Targeted release: I propose this change for Fedora 32
Last updated: Jan 5 2020
Pagure.io issue: https://pagure.io/releng/issue/9127
I was unable to create an article in Fedora wiki system.
As of Fedora 31, the LiveOS/squashfs.img file on the installation image, is
compressed with default settings of mksquashfs. The standard configuration
is set to XZ algorithm with block size of 128k and BCJ filter enabled.
Those parameters can be adjusted which will lead to a better compression
ratio and/or reduction of the CPU usage at build time.
This is simple to achieve. Recently, Lorax has gotten support for
adjusting the compression options for mksquashfs via the configuration
file. The file should be altered as following:
bcj = yes
args = -b 1M -Xdict-size 1M -no-recovery
Where -b 1M and -Xdict-size 1M are block and dictionary sizes respectively.
Could be adjusted.
Benefit to Fedora
Reduction of the installation media size and the cost of storing and
Reduction of the CPU usage at build time. Depending on which compression
See a graphical detail at https://pagure.io/releng/issue/9127
The build environment should have support for adjusting the Lorax
configuration file.. Lorax is a program that produces the
LiveOS/squashfs.img file on the installation media.
One of the way to allow for such customization, is to add a feature in
Pungi, to allow for passing -c option to Lorax.
Release engineering: #9127 <https://pagure.io/releng/issue/9127>
Policies and guidelines: N/A
Trademark approval: N/A
This change comes at a cost of higher memory usage during the
installation. Based on my personal estimations, this should not be the
issue. Since the decompression should require up to 1MiB per thread.
Increasing the block size on the current configuration with EXT4 file
system, should increase latency while accessing the EXT4 filesystem. The
exact impact is to be evaluated.
The impact of latency will be reduced, if the plain SquashFS option is
Release notes See also
Release Configuration Management engineer