Linux kernel/Image Size

Vision

Reduce the flash and memory footprint of the linux-yocto generated kernel to boot with 8MB of memory and allow for a minimal image in under 8MB of flash. The uncompressed kernel image should come in around 1.5MB. Changes to the kernel shall not impact POSIX compliance.

Design

The majority of the work here will center around CONFIG options. There is a start of a kernel type variant already in the linux-yocto tree, called "small" which modifies the CONFIG for a smaller image. The output of this effort will mostly modify that mechanism. Major optional parameters, like disabling the block layer perhaps, will be created as peers to the "small" mechanism. These can be enabled in the recipe itself via:

KERNEL_FEATURES += "small noblock"

The approach will be to minimize the image as far as possible with existing infrastructure without creating very specialized hacks that must be continually maintained outside of mainline. If it turns out that we can make significant improvements to the sources or the configuration of the kernel to reduce image size, that development will be performed upstream-first, in the usual fashion.

An audit of linux-tiny will determine if there are patches remaining there that we should help get included upstream.

Resources

• http://elinux.org/Kernel_Size_Tuning_Guide
• http://elinux.org/Kernel_Size_Tuning_Guide_Config_Option_Impact
• http://elinux.org/System_Size
• http://elinux.org/Linux_Tiny

Results

Initial Beagleboard (refresh v2 21-Jun-2011)

$ ls -la ./arch/arm/boot/uImage
-rw-rw-r-- 1 dvhart dvhart 2738416 2011-06-20 23:19 ./arch/arm/boot/uImage

$ size ./arch/arm/boot/vmlinux
   text	   data	    bss	    dec	    hex	filename
5527685	 338944	 272776	6139405	 5dae0d	./arch/arm/boot/vmlinux