<para>
Very small distributions have some significant advantages such
- as requiring less on-die memory (cheaper), better performance
- through efficient cache usage, lower power requirements due to less
- memory, faster boot times, and reduced development overhead.
+ as requiring less on-die or in-package memory (cheaper), better
+ performance through efficient cache usage, lower power requirements
+ due to less memory, faster boot times, and reduced development
+ overhead.
Some real-world examples where a very small distribution gives
you distinct advantages are digital cameras, medical devices,
- small headless systems, and partitioned flash.
+ and small headless systems.
</para>
<para>
<para>
The following list presents the overall steps you need to
- consider and perform to create very small systems that
- have a kernel and root filesystem under 4 Mbytes, boot to the
- shell in under two seconds, maintain <filename>ipv4</filename>
- functionality, and avoid an initial RAM disk:
+ consider and perform to create distributions with smaller
+ filesystems, faster boot times, maintain your critical
+ functionality, and avoid initial RAM disks:
<itemizedlist>
<listitem><para>Determine your goals and guiding
principles.</para></listitem>
</para></listitem>
<listitem><para>Do not create any difficult "hacks"
to achieve your goals.</para></listitem>
- <listitem><para>Leverage off the device-specific
+ <listitem><para>Leverage the device-specific
options.</para></listitem>
<listitem><para>Work in a separate layer so that you
keep changes isolated.
Memory consists of static, dynamic, and temporary memory.
Static memory is the TEXT (the code), DATA (initialized data
in the code), and BSS (uninitialized data) sections.
- Dynamic memory contains memory that is allocate at runtime,
+ Dynamic memory contains memory that is allocated at runtime,
stacks, hash tables, and so forth.
Temporary memory is decompressed from the expanded kernel
- after boot.
- Temporary memory also includes the <filename>__init__</filename>
+ after boot and also includes the <filename>__init__</filename>
functions.
</para>
the <filename>scripts</filename> directory:
<itemizedlist>
<listitem><para><filename>ksize.py</filename>: Reports
- the size of the kernel files.</para></listitem>
+ component sizes for the kernel files.</para></listitem>
<listitem><para><filename>dirsize.py</filename>: Reports
- the size of the root filesystem.</para></listitem>
+ component sizes for root filesystem.</para></listitem>
</itemizedlist>
This next tool and command helps you organize configuration
fragments and view file dependencies in a human-readable form:
section of the Yocto Project Linux Kernel Development
Manual and the "<link linkend='creating-config-fragments'>Creating Configuration Fragments</link>"
section, which is in this manual.</para></listitem>
- <listitem><para><filename>bitbake -u depexp -g core-image-*</filename>:
+ <listitem><para><filename>bitbake -u depexp -g <bitbake_target></filename>:
Using the BitBake command with these options brings up
a Dependency Explorer from which you can view file
dependencies.
Understanding these dependencies allows you to make
- sane decisions when cutting out various pieces of the
+ informed decisions when cutting out various pieces of the
kernel and root filesystem.</para></listitem>
</itemizedlist>
</para>
<para>
First, check out what is hogging your file system running the
- <filename>dirsize.sh</filename> script from your root directory:
+ <filename>dirsize.py</filename> script from your root directory:
<literallayout class='monospaced'>
$ cd <root-directory-of-image>
$ dirsize.py 100000 > dirsize-100k.log
You can apply a filter to the script to ignore files under
a certain size.
This example filters out anything below 100 Kbytes.
+ The sizes reported by the tool are uncompressed and thus,
+ will be smaller by a relatively constant factor in a
+ compressed root filesystem.
When you examine your log file, you can focus on areas of the
root filesystem that take up large amounts of memory.
</para>
result in minimal impact on the feature set.
For example, you might not need a VGA display.
Or, you might be able to get by with <filename>devtmpfs</filename>
- and <filename>mdev</filename>.
+ and <filename>mdev</filename> instead of
+ <filename>udev</filename>.
</para>
<para>
</para>
<para>
- Some other examples of where you can look to eliminate size
- from the root filesystem are using <filename>ext2</filename>
- rather than <filename>ext3</filename>, which requires a
- 1 Mbyte journal.
+ Finally, you should consider exactly what filesystem you need
+ to meet your needs while also reducing size.
+ For example, consider <filename>cramfs</filename>,
+ <filename>squashfs</filename>, <filename>ubifs</filename>,
+ <filename>ext2</filename>, or an <filename>initramfs</filename>
+ using <filename>initramfs</filename>.
+ Be aware that <filename>ext3</filename> requires a 1 Mbyte
+ journal.
If you are okay with running read-only you don't need this
journal.
</para>
taken up with the built-in <filename>.o</filename> files for
drivers, networking, core kernel files, filesystem, sound,
and so forth.
+ The sizes reported by the tool are uncompressed and thus,
+ will be smaller by a relatively constant factor in a compressed
+ kernel image.
Look to reduce the areas that are large and taking up around
the "90% rule".
</para>
projects / thirdparty / openembedded / openembedded-core-contrib.git / commitdiff
