Compcache

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 * '''Created''': [[Date(2008-06-11T23:14:46Z)]] by OliverGrawert
 * '''Contributors''': OliverGrawert
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 Compcache provides a possibility of using parts of the memory as virtual compressed swapdevice. We want to include this functionality in Ubuntu Intrepid to lower memory requirements in various setups.
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 Most notably the minimal system requirements will be affected by this, there should be no separate release note for this feature.
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The RAM requirements for running an ubuntu desktop are currently very high. Especially on LiveCDs and Thin Clients this high demand is noticeable. Additionally there are more and more users with low specced subnotebooks within the ubuntu userbase that have a requirement for being able to run the system on a limited amount of memory. With the Google Summer of Code project [http://code.google.com/p/compcache/ compcache] it is possible to extend the available physical ram with a virtual swapdevice, this technology will be included in ubuntu.
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=== Code Changes === = Related Bugs =
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Add compcache modules, allowing ubiquity installs on 256MB machines:
https://bugs.launchpad.net/ubuntu/+bug/200765

Xubuntu requires more than 128mb of ram to install via LiveCD:
https://bugs.edge.launchpad.net/ubuntu/+source/xubuntu-meta/+bug/70561

== Outstanding Issues ==

* CPU usage has to be reviewed
  - Works on the principle of swap replay; swap in/out events are relayed to userspace, where it is compressed
* a cleaner way than the included initscripts should be found and integration
  with udev for the device creation is needed
* what is the impact on suspend/hibernate/resume ?
  Apparently there are some known problems http://code.google.com/p/compcache/issues/detail?id=2
  talking about freezes on ARM architecture. Since ARM does suspend completely different
  (the clock is separated from the CPU, so ARM shuts down completely while x86 CPUs have an internal
  clock and never power down completely on suspend) it might not be an issue at all on x86 based CPUs.
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 * use the liveCD default session on a machine with 256M
 * use a thin client with 32M

Please check the status of this specification in Launchpad before editing it. If it is Approved, contact the Assignee or another knowledgeable person before making changes.

Summary

  • Compcache provides a possibility of using parts of the memory as virtual compressed swapdevice. We want to include this functionality in Ubuntu Intrepid to lower memory requirements in various setups.

Release Note

  • Most notably the minimal system requirements will be affected by this, there should be no separate release note for this feature.

Rationale

The RAM requirements for running an ubuntu desktop are currently very high. Especially on LiveCDs and Thin Clients this high demand is noticeable. Additionally there are more and more users with low specced subnotebooks within the ubuntu userbase that have a requirement for being able to run the system on a limited amount of memory. With the Google Summer of Code project [http://code.google.com/p/compcache/ compcache] it is possible to extend the available physical ram with a virtual swapdevice, this technology will be included in ubuntu.

Use Cases

Design

Implementation

Related Bugs

Add compcache modules, allowing ubiquity installs on 256MB machines: https://bugs.launchpad.net/ubuntu/+bug/200765

Xubuntu requires more than 128mb of ram to install via LiveCD: https://bugs.edge.launchpad.net/ubuntu/+source/xubuntu-meta/+bug/70561

Outstanding Issues

* CPU usage has to be reviewed

  • - Works on the principle of swap replay; swap in/out events are relayed to userspace, where it is compressed

* a cleaner way than the included initscripts should be found and integration

  • with udev for the device creation is needed

* what is the impact on suspend/hibernate/resume ?

  • Apparently there are some known problems http://code.google.com/p/compcache/issues/detail?id=2 talking about freezes on ARM architecture. Since ARM does suspend completely different (the clock is separated from the CPU, so ARM shuts down completely while x86 CPUs have an internal clock and never power down completely on suspend) it might not be an issue at all on x86 based CPUs.

Test/Demo Plan

  • use the liveCD default session on a machine with 256M
  • use a thin client with 32M

BoF agenda and discussion

CategorySpec

Compcache (last edited 2008-08-06 16:41:47 by localhost)