Fedora 32 system-wide change proposal: reduce installation media size by improving the compression ratio of SquashFS filesystem

Bohdan Khomutskyi <bkhomuts@xxxxxxxxxx> · Sun, 5 Jan 2020 13:23:12 +0100



    Summary
    Improve compression ratio of SquashFS filesystem on the
      installation media.
    Owner
    Name: Bohdan Khomutskyi
    Email: bkhomuts@xxxxxxxxxx
    Current status
    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.

    
    Detailed Description
    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[1]
            for adjusting the compression options for mksquashfs via the
            configuration file. The file should be altered as following:
    
      [compression]

            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 distributing Fedora.
      
      
        Reduction of the CPU usage at build time. Depending on which
          compression parameters chosen.
      
      
        See a graphical detail at https://pagure.io/releng/issue/9127.
      
    
    Scope
    
      
        Proposal owners:
      
    
    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
      
      
        Policies and
                        guidelines: N/A
      
      
        Trademark approval:
                        N/A
      
    
    Upgrade/compatibility impact
    
      
        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.
      
    
    User Experience
    
      
        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 be choosen.
      
    
    Dependencies
    
      
        N/A
      
    
    Contingency Plan
    
      
        N/A
      
    
    Documentation
https://pagure.io/releng/issue/9127.

    mksquashfs(1)
    Release notes
    See also
    https://pagure.io/releng/issue/8646
    --

    
    Bohdan Khomutskyi
    Release Configuration
      Management engineer

      Red Hat
Attachment:
Proposed change -- Improve the compression ration of squashfs.img.pdf

Description: Adobe PDF document
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