From: eLinux.org

Size Tunables

This page has a list of items that can be configured for the Linux kernel, which may affect the size (RAM/ROM/static/dynamic) of the kernel.

CONFIG option	description	default value	value for small size	Size change (ARM)	Notes
CONFIG_CORE_SMALL	tune some kernel data sizes	N	Y	??	.
CONFIG_NET_SMALL	tune some net-related data sizes	N	Y	??	.
CONFIG_PRINTK	allow disable of printk code and message data	Y	N	??	.
CONFIG_BUG	allow elimination of BUG (and BUG_ON??) code	Y	N	??	.
CONFIG_ELF_CORE	allow disabling of ELF core dumps	Y	N	??	.
CONFIG_PROC_KCORE	allow disabling of /proc/kcore	Y	N	??	.
CONFIG_AIO	allow disabling of async IO syscalls	Y	N	??	.
CONFIG_XATTR	allow disabling of xattr syscalls	Y	N	??	.
CONFIG_FILE_LOCKING	allow disabling of file locking syscalls	Y	N	??	.
CONFIG_DIRECTIO	allow disabling of direct IO support	Y	N	??	.
CONFIG_MAX_SWAPFILES_SHIFT	number of swapfiles	5	0	??	.
CONFIG_NR_LDISCS	number of tty line disciplines	16	2?	??	.
CONFIG_MAX_USER_RT_PRIO	number of RT priority levels (schedule slots)	100	5?	??	.
Other config options	These are not in Linux-tiny, but help with size	default	small	Size change (ARM)	Notes
CONFIG_KALLSYMS	load all symbols for debugging/kksymoops	Y	N	??	.
CONFIG_SHMEM	allow use of shmem filesystem	Y	N	??	.

Options for measuring size	description	default value	value for instrumentation
CONFIG_KMALLOC_ACCOUNTING	turn on kmalloc accounting	N	Y
CONFIG_AUDIT_BOOTMEM	print out all bootmem allocations	N	Y
CONFIG_DEPRECATE_INLINES	cause compiler to emit info about inlines	N	Y

options that should be investigated

Option	default value	value for small size	Size change	Notes
CONFIG_SERIAL_8250_NR_UARTS	4	0	??	only useful for non-legacy ports, depends on hardware, but most embedded hardware has only legacy serial ports

- by default (at least on my OSK config), several different schedulers are configured