Features/LZMA for Live Images

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== Summary ==
 
== Summary ==
Enabling LZMA for compression to allow us ship more software on our live images.
+
Enabling XZ (a variant of LZMA) for compression to allow us ship more software on our live images.
  
 
== Owner ==
 
== Owner ==
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== Current status ==
 
== Current status ==
 
* Targeted release: [[Releases/15 | Fedora 15 ]]
 
* Targeted release: [[Releases/15 | Fedora 15 ]]
* Last updated: 2010-12-24
+
* Last updated: 2011-03-06
* Percentage of completion: 10%
+
* Percentage of completion: 100%
  
 
== Detailed Description ==
 
== Detailed Description ==
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== Scope ==
 
== Scope ==
 
* kernel
 
* kernel
** Lougher needs to do a new set of patches since the ones for 2.6.34 were only partially accepted.
+
** F15 has had 2.6.38 kernels for a while and XZ is working fine.
*** We are still waiting for Lougher to have a chance to get an acceptable patch (to Linus) for the Linus kernel. If it gets into 2.6.38 we will have no trouble getting this into F15.
+
*** Statements from Lougher:
+
**** https://bugzilla.redhat.com/show_bug.cgi?id=504425#c19
+
**** http://marc.info/?l=linux-kernel&m=127190194229951&w=2
+
*** It looks like [http://git.kernel.org/?p=linux/kernel/git/pkl/squashfs-lzma.git;a=summary some patches] were being worked on, but weren't ready for 2.6.35 (or 2.6.36) as there was no pull request for them.
+
** [http://sourceforge.net/mailarchive/forum.php?forum_name=squashfs-devel&max_rows=25&style=nested&viewmonth=201011 Discussion] about lzma / xz support in the kernel on the squashfs-devel list.
+
** New development related to xz (lzma2) and squashfs kernel support:
+
*** [http://marc.info/?l=linux-kernel&m=129187477131797&w=2 Lougher's patch thread] on lkml.
+
*** [http://marc.info/?l=linux-kernel&m=129131729423308&w=2 Lasse Collin's XZ patch thread] on lkml.
+
*** [http://git.kernel.org/?p=linux/kernel/git/pkl/squashfs-xz.git;a=summary XZ and squashfs patch repo] relative to 2.6.36.
+
*** [http://sourceforge.net/projects/squashfs/develop Development version of squashfs-tools] which includes XZ support.
+
 
** Fallback plan for the kernel is to do nothing.
 
** Fallback plan for the kernel is to do nothing.
 
* livecd-creator
 
* livecd-creator
 
** Changes to livecd-creator:
 
** Changes to livecd-creator:
*** Change the default compression type to xz.
+
*** Change the default compression type to xz. (Done - in rawhide)
*** Update the documentation to reflect the changed default.
+
*** Update the documentation to reflect the changed default. (Done - in rawhide)
 
*** These changes won't be made until after the kernel feature is available, so no fallback is needed.
 
*** These changes won't be made until after the kernel feature is available, so no fallback is needed.
 
* squashfs-tools
 
* squashfs-tools
** squashfs-tools is back on the table as XZ (LZMA2) will be separate from LZMA.
+
*** The 4.2 release is now in rawhide and F15 testing.
** The development version needs to get built and tested.
+
*** A 4.2 prerelease build is now in rawhide.
+
** The squashfs-tools 4.2 release is tentatively planned for mid-February.
+
 
** A [https://fedoraproject.org/wiki/QA:Testcase_squashfs-tools_compression test case] has been created to make it easier to get critical path testing.
 
** A [https://fedoraproject.org/wiki/QA:Testcase_squashfs-tools_compression test case] has been created to make it easier to get critical path testing.
 +
* Out of scope is taking advantage of squashfs-tools new compression specific options.
 +
** They will probably be exposed in some way in livecd-creator for F16 if it looks like they are useful to tweak for live images. But that won't be a feature.
  
 
== How To Test ==
 
== How To Test ==
 
* We need to make sure live images work.
 
* We need to make sure live images work.
* We need to make sure live images are smaller using LZMA2 (xz) compression.
+
** The nightly builds are now using xz compression.
 +
** The Desktop spin from the nightly composes boots successfully from a live USB drive.
 +
* We need to make sure live images are smaller using LZMA2 (XZ) compression.
 +
** A test games spin from 2011-01-21 rawhide + a 2.6.38 scratch build went from 4499222528 bytes to 4111771648 bytes (8.6% decrease).
 +
** A test desktop spin dropped from 753926144 bytes to 613416960 bytes (18.6% decrease).
 
* We need to make sure performance is acceptable.
 
* We need to make sure performance is acceptable.
** Using a live image needs to not be noticeably slower (hopefully it will be faster with typcial hardware) with LZMA than with gzip compression.
+
** Using a live image needs to not be noticeably slower (hopefully it will be faster with typcial hardware) with LZMA than with GZIP compression.
** Making a compressed file system using LZMA can be somewhat slower than with gzip, because commonly time isn't as critical when making the image (compared to using it).
+
*** The speed seemed comparable when run off a USB drive.
** We need to test unsquashing squashed images work using unsquashfs (both LZMA and gzip).
+
** It is OK if making a compressed file system using xz is somewhat slower than with gzip, because commonly time isn't as critical when making the image (compared to using it).
* Specific test cases: (Note in early testing, the default will be gzip rather than lzma.)
+
** squashfs-tools should be [https://fedoraproject.org/wiki/QA:Testcase_squashfs-tools_compression tested] to make sure all of the compression methods work.
** Squashfs 4.1
+
* Specific test cases: (Note in early testing, the default will be gzip rather than xz.)
 +
** Squashfs 4.2
 
*** No --compression-type
 
*** No --compression-type
 
**** Should build using xz and image should work.
 
**** Should build using xz and image should work.
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**** Should build using gzip and image should work.
 
**** Should build using gzip and image should work.
 
*** --compression-type=xz
 
*** --compression-type=xz
**** Should build using lzma and image should work with a kernel that supports lzma squashfs.
+
**** Should build using xz and image should work with a kernel that supports xz squashfs.
 
**** The image should be smaller than with gzip compression.
 
**** The image should be smaller than with gzip compression.
**** The image should run nearly as fast or faster than with gzip compression on common hardware.
+
**** The image should run nearly as fast or faster than when using gzip compression on common hardware.
**** The time needed to build the image should not be inordinately longer than with gzip on common hardware.
+
**** The time needed to build the image should not be inordinately longer than when using gzip on common hardware.
*** --compression-type=garbage
+
**** A reasonable error message should be displayed
+
*** Test using a 2.6.33 kernel (with gzip) to make sure the xattr feature doesn't cause a problem for kernels that don't support that in squashfs file systems.
+
*** Test livecd-iso-to-disk on an image using lzma with a system with a 4.0 version of squashfs-tools.
+
*** Test livecd-iso-to-disk on an image using gzip with a system with a 4.0 version of squashfs-tools.
+
** Squashfs 4.0
+
*** No --compression-type
+
**** A reasonable error message should be displayed
+
*** --compression-type=gzip
+
**** Should build using gzip and image should work.
+
*** --compression-type=xz
+
**** A reasonable error message should be displayed
+
 
*** --compression-type=garbage
 
*** --compression-type=garbage
 
**** A reasonable error message should be displayed
 
**** A reasonable error message should be displayed
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== Dependencies ==
 
== Dependencies ==
 
* kernel (may need to ask for backport)
 
* kernel (may need to ask for backport)
 +
** This is unlikely. If the patches don't make it into 2.6.38, then due to kernel release timing it will be better to slip to F16.
 
* livecd-tools
 
* livecd-tools
 +
* Spin creation process
 +
** I have started a [https://fedorahosted.org/rel-eng/ticket/4343 dialogue] with releng about this.
  
 
== Contingency Plan ==
 
== Contingency Plan ==
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== Release Notes ==
 
== Release Notes ==
  
* Mention the squashfs version change, that it supports LZMA compression, point to its documentation and note that it is supported in the kernel as well.
+
* Mention the squashfs version change, that it supports XZ (LZMA2) compression, point to its documentation and note that it is supported in the kernel as well.
* Mention that livecd-creator uses LZMA by default, how to get gzip compression if desired for use with older kernels or other reasons.
+
**I have noted this in the file systems beat.
 +
* Mention that livecd-creator uses XZ by default, how to get GZIP compression if desired for use with older kernels or other reasons.
 +
** I have something in the doc beats about this.
  
 
== Thanks ==
 
== Thanks ==
  
I would like to thank Phillip Lougher for his work on squashfs. The key work needed for this feature was done by Phillip upstream.
+
I would like to thank Phillip Lougher for his work on squashfs and Lasse Collin for getting XZ squashfs support in the 2.6.38 kernel. Most of the work for this feature was done by them upstream.
  
 
== Comments and Discussion ==
 
== Comments and Discussion ==

Latest revision as of 17:42, 15 May 2011

Contents

[edit] LZMA for Live Images

[edit] Summary

Enabling XZ (a variant of LZMA) for compression to allow us ship more software on our live images.

[edit] Owner

  • Email: <bruno@wolff.to>

[edit] Current status

  • Targeted release: Fedora 15
  • Last updated: 2011-03-06
  • Percentage of completion: 100%

[edit] Detailed Description

LZMA compression typically provides better compression than gzip while still providing relatively fast uncompression. Once squashfs file systems are supported by the kernel we can use them for building live images. A test with the games spin resulted in a 8.7% reduction (from 4242538496 bytes to 3873439744 bytes) in size of the resulting live image.

[edit] Benefit to Fedora

By allowing more packages to be put on a Live Image, we can make a few of our space constrained images better. For other images, having them be smaller will make them faster to download.

[edit] Scope

  • kernel
    • F15 has had 2.6.38 kernels for a while and XZ is working fine.
    • Fallback plan for the kernel is to do nothing.
  • livecd-creator
    • Changes to livecd-creator:
      • Change the default compression type to xz. (Done - in rawhide)
      • Update the documentation to reflect the changed default. (Done - in rawhide)
      • These changes won't be made until after the kernel feature is available, so no fallback is needed.
  • squashfs-tools
      • The 4.2 release is now in rawhide and F15 testing.
    • A test case has been created to make it easier to get critical path testing.
  • Out of scope is taking advantage of squashfs-tools new compression specific options.
    • They will probably be exposed in some way in livecd-creator for F16 if it looks like they are useful to tweak for live images. But that won't be a feature.

[edit] How To Test

  • We need to make sure live images work.
    • The nightly builds are now using xz compression.
    • The Desktop spin from the nightly composes boots successfully from a live USB drive.
  • We need to make sure live images are smaller using LZMA2 (XZ) compression.
    • A test games spin from 2011-01-21 rawhide + a 2.6.38 scratch build went from 4499222528 bytes to 4111771648 bytes (8.6% decrease).
    • A test desktop spin dropped from 753926144 bytes to 613416960 bytes (18.6% decrease).
  • We need to make sure performance is acceptable.
    • Using a live image needs to not be noticeably slower (hopefully it will be faster with typcial hardware) with LZMA than with GZIP compression.
      • The speed seemed comparable when run off a USB drive.
    • It is OK if making a compressed file system using xz is somewhat slower than with gzip, because commonly time isn't as critical when making the image (compared to using it).
    • squashfs-tools should be tested to make sure all of the compression methods work.
  • Specific test cases: (Note in early testing, the default will be gzip rather than xz.)
    • Squashfs 4.2
      • No --compression-type
        • Should build using xz and image should work.
      • --compression-type=gzip
        • Should build using gzip and image should work.
      • --compression-type=xz
        • Should build using xz and image should work with a kernel that supports xz squashfs.
        • The image should be smaller than with gzip compression.
        • The image should run nearly as fast or faster than when using gzip compression on common hardware.
        • The time needed to build the image should not be inordinately longer than when using gzip on common hardware.
      • --compression-type=garbage
        • A reasonable error message should be displayed
    • man livecd-creator
      • Should have the --compression-type option documented with the correct default. (gzip in eary testing, xz in later testing.)
    • livecd-creator --help
      • Should have the --compression-type option documented with the correct default. (gzip in eary testing, xz in later testing.)

[edit] User Experience

Live images will be smaller or have more included packages.

[edit] Dependencies

  • kernel (may need to ask for backport)
    • This is unlikely. If the patches don't make it into 2.6.38, then due to kernel release timing it will be better to slip to F16.
  • livecd-tools
  • Spin creation process
    • I have started a dialogue with releng about this.

[edit] Contingency Plan

  • Since there isn't really anything further to do until the kernel feature is available, the fallback is pretty much not to do anything.

[edit] Documentation

  • Most likely livecd-creator would be getting a new option and would need its help updated along with the code changes.

[edit] Release Notes

  • Mention the squashfs version change, that it supports XZ (LZMA2) compression, point to its documentation and note that it is supported in the kernel as well.
    • I have noted this in the file systems beat.
  • Mention that livecd-creator uses XZ by default, how to get GZIP compression if desired for use with older kernels or other reasons.
    • I have something in the doc beats about this.

[edit] Thanks

I would like to thank Phillip Lougher for his work on squashfs and Lasse Collin for getting XZ squashfs support in the 2.6.38 kernel. Most of the work for this feature was done by them upstream.

[edit] Comments and Discussion