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start [2017-01-21 22:38] joshtriplett Add note about nm --size-sort. |
start [2020-07-06 21:27] joshtriplett Minor formatting updates |
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| ====== Building a tiny kernel ====== | ====== Building a tiny kernel ====== | ||
| - | With Linux 3.17-rc1 and newer, ''make tinyconfig'' will produce a minimal kernel. You can then turn on the minimal set of options you need. | + | With current Linux (since 3.17-rc1 and newer, ''make tinyconfig'' will produce a minimal kernel. You can then turn on the minimal set of options you need. |
| - | + | ||
| - | On previous kernels, you'll need to take a few additional steps to make the kernel as small as possible: | + | |
| - | + | ||
| - | * Prior to 3.15-rc1, ''make allnoconfig'' did not turn off options behind CONFIG_EXPERT or CONFIG_EMBEDDED, so you'll have to do so manually. | + | |
| - | * Change the allocator from SLUB to SLOB | + | |
| - | * Change the kernel compression method from GZIP to XZ | + | |
| - | * Disable HIGHMEM4G, using NOHIGHMEM instead | + | |
| - | * Set ''CONFIG_OPTIMIZE_INLINING=y'' | + | |
| - | * Set ''CONFIG_CC_OPTIMIZE_FOR_SIZE=y'' | + | |
| You'll want to target the most code-size-efficient architecture supported by your target machine; for instance, on x86 systems, build a 32-bit kernel rather than a 64-bit kernel. On current kernels, ''make allnoconfig'' should do this automatically. | You'll want to target the most code-size-efficient architecture supported by your target machine; for instance, on x86 systems, build a 32-bit kernel rather than a 64-bit kernel. On current kernels, ''make allnoconfig'' should do this automatically. | ||
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| ====== Submitting tinification changes ====== | ====== Submitting tinification changes ====== | ||
| - | When submitting a change to make the kernel smaller, use ''scripts/bloat-o-meter'' to compare the size of the old and new vmlinux, overall and broken out by symbol. Include the bloat-o-meter output in your commit message. | + | When submitting a change to make the kernel smaller, use ''scripts/bloat-o-meter'' to compare the size of the old and new ''vmlinux'', overall and broken out by symbol. Include the ''bloat-o-meter'' output in your commit message. |
| - | Most new configuration options added as part of this effort should depend on CONFIG_EMBEDDED or CONFIG_EXPERT. | + | When introducing a new configuration option for an existing kernel feature, the new option should likely depend on ''CONFIG_EXPERT''. |
| - | If your changes affect the size of the decompression stub, you may additionally need to run bloat-o-meter on the stub. | + | If your changes affect the size of the decompression stub, you may additionally need to run ''bloat-o-meter'' on the stub. |
| - | When adding a new Kconfig symbol, to confirm that you've added any necessary dependencies on that symbol, build an "allyesconfig" kernel with only your new symbol (and anything depending on it) turned off. Build failures related to the bits your new symbol compiles out will identify additional dependencies you need. | + | When adding a new Kconfig symbol, to confirm that you've added any necessary dependencies on that symbol, build an ''allyesconfig'' kernel with only your new symbol (and anything depending on it) turned off. Build failures related to the bits your new symbol compiles out will identify additional dependencies you need. |
| - | You can find the latest tinification changes in Josh Triplett's tree at https://git.kernel.org/cgit/linux/kernel/git/josh/linux.git/ , in the tiny/* branches. Note that tiny/next gets reset for each new merge window, and other tiny/* branches may be recreated or rebased. | + | You can find the latest tinification changes in Josh Triplett's tree at https://git.kernel.org/cgit/linux/kernel/git/josh/linux.git/ , in the ''tiny/*'' branches. Note that tiny/next gets reset for each new merge window, and other ''tiny/*'' branches may be recreated or rebased. |
| ====== Searching for tinification opportunities ====== | ====== Searching for tinification opportunities ====== | ||
| - | On a built kernel, try running ''nm --size-sort vmlinux''. This will show all the symbols in vmlinux, sorted by size. | + | On a built kernel, try running ''nm --size-sort vmlinux''. This will show all the symbols in ''vmlinux'', sorted by size. |
| ====== Use Cases ====== | ====== Use Cases ====== | ||
| See the [[Use Cases]] page. | See the [[Use Cases]] page. | ||
start.txt · Last modified: 2020-07-06 21:27 by joshtriplett
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