Kernel Size Reduction Work

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This page has a list of of recent (as of 2014) ideas and projects for Linux kernel size reduction.

As of June, 2014, Linux Tiny was no longer maintained. However, new efforts to support Linux as a viable option on micro-controllers and deeply embedded systems have led to renewed interest in extreme size reduction of the kernel. Some good projects were described at ELC 2014.

Recent work

List of recently used techniques

Vitaly Wool's project

  • kernel XIP
  • dietnet
  • ARM thumb mode
  • application XIP on squashfs

micro-yocto project

  • net-diet
  • LTO
  • SYSFS_SYSCALL
  • USELIB
  • BUG_ON
  • X86_IOPORT
  • CONFIG_PTRACE
  • CONFIG_SIGNALS
  • no sys_sendfile
  • network reductions:
    • replace kernel stack with user-space stack (LWIP)
    • TCP/UDP echo (requires app changes)

instrumentation

microYocto tracing hash triggers

auto-reduce

  • LTO
  • syscall filtering
  • command line filtering
  • global constraints
  • kernel stack size

Ideas for new reductions

  • trace-guided optimization
  • cold code compression
    • use U of Gent code to re-try cold code compression

People or groups interested in size reductions

individuals

  • Josh Triplett - e-mail:josh at joshtriplett dot org
    • new linux tiny patches
  • Tom Zanussi - e-mail: tom dot zanussi at linux dot intel dot com
    • microYocto
  • Andi Kleen - e-mail: ak at linux dot intel dot com
    • netdiet patches
  • Alan Cox - email: alan dot cox at linux dot intel dot com
  • Shinsuke Kato - e-mail: kato dot shinsuke at jp dot panasonic dot com
  • Tim Bird - e-mail: tim dot bird at sonymobile dot com
    • auto-reduce stuff
  • Vitaly Wool - e-mail: vitaly dot wool at softprise dot net
    • extreme microcontroller Linux (<256K RAM)
  • Phil Blundell - e-mail:
    • meta-micro (OE-based small distro - last work in 2012)

companies

  • Emcraft Systems sells a variety of microcontroller-based boards and products

Meetings and Discussions

Kernel Summit 2014

Josh Triplett has proposed a session discussing size issues at the 2014 Kernel Summit. His draft list of proposed topics was the following: Topics:

  • An overview of why the kernel's size still matters today ("but don't we all have tons of memory and storage?")
  • Tiny in RAM versus tiny on storage.
  • How much the kernel has grown over time.
  • How size regressions happen and how to avoid them
  • Size measurement, bloat-o-meter, allnoconfig, and other tools
  • Compression and the decompression stub
  • Kconfig, and avoiding excessive configurability in the pursuit of tiny
  • Optimizing a kernel for its exact target userspace.
  • Examples of shrinking the kernel
  • Discussion on proposed ways to make the kernel tiny, how much they might save, how much work they'd require, and how to implement them with minimal impact to the un-shrunken common case.

(see http://lists.linuxfoundation.org/pipermail/ksummit-discuss/2014-May/000001.html for the discussion thread)

Size/IOT summit at ELC Europe 2014

We are considering holding a Size/IOT meeting at ELC Europe. Details will be placed here should this meeting end up being organized.