Global build settings / Kernel build options / Crash logging
CONFIG_KERNEL_CRASHLOG
Global build settings / Kernel build options / Support for paging of anonymous memory (swap)
CONFIG_KERNEL_SWAP
Global build settings / Kernel build options / Compile the kernel with symbol table information
CONFIG_KERNEL_KALLSYMS
Global build settings / Kernel build options / Compile the kernel with debug information
CONFIG_KERNEL_DEBUG_INFO
CONFIG_KERNEL_DEBUG_KERNEL (unset by disabling CONFIG_KERNEL_INFO)
Global build settings / Kernel build options / Enable process core dump support
CONFIG_KERNEL_ELF_CORE
CONFIG_KERNEL_COREDUMP (unset by disabling CONFIG_KERNEL_ELF_CORE)
Global build settings / Kernel build options / Compile the kernel with SysRq support
KERNEL_MAGIC_SYSRQ
Kernel modules / Wireless Drivers / kmod-mac80211 / Export mac80211 internals in DebugFS
PACKAGE_MAC80211_DEBUGFS
Kernel modules / Wireless Drivers / kmod-mac80211 / Enable 802.11s mesh support
PACKAGE_MAC80211_MESH
I also tested disabling printk, but the kernel log disappeared completely, and disabling kernel debug fs made the overlay file system disappear so it used a temporary RAM FS instead.
Things that can be enabled to save space:
Global build settings / Strip unnecessary exports from the kernel image
CONFIG_STRIP_KERNEL_EXPORTS=y
Global build settings / Strip unnecessary functions from libraries
CONFIG_USE_MKLIBS=y
On systems with little RAM it may help to enable these:
Base system
PACKAGE_zram-swap
Base system / procd Configuration
PROCD_ZRAM_TMPFS
If you are low on RAM you should also run make kernel_menuconfig and set fragments cached = 1, especially if you increased the block size.
File systems / Miscellaneous filesystems / Additional option for memory-constrained systems / Number of fragments cached
SQUASHFS_EMBEDDED=y
CONFIG_SQUASHFS_FRAGMENT_CACHE_SIZE=1
The savings aren't radical. Maybe 100-300 KB in total, but sometimes that's what's needed. I hope others will add their suggestions about what can be removed or information about what bad may happen if you do. Maybe I'll write a separate wiki page about optimizations later.
Use the "normal" firmware instead of the Candela Technologies (CT). I don't recommend doing it at all, and would suggest to enable the requested feature instead.
there is a big problem I have done like on the wiki and in this forum, I have made it and succeeded in continuing my flash to the router and it was not as sweet as I hoped, the router was experiencing failsafe mode. I followed the instructions on the wiki and in this forum Modifying build configuration variables
Modifying build configuration variables
You can also save space by changing configuration variables using make menuconfig. In addition to the ones mentioned here you can save a tiny bit of space by disabling commands in busybox.
Options that can be disabled to save space.
Config variable Menu path Estimated savings
CONFIG_KERNEL_PRINTK Global build settings / Kernel build options / Enable support for printk
CONFIG_KERNEL_CRASHLOG Global build settings / Kernel build options / Crash logging
CONFIG_KERNEL_SWAP Global build settings / Kernel build options / Support for paging of anonymous memory (swap)
CONFIG_KERNEL_KALLSYMS Global build settings / Kernel build options / Compile the kernel with symbol table information
CONFIG_KERNEL_DEBUG_INFO Global build settings / Kernel build options / Compile the kernel with debug information
CONFIG_KERNEL_ELF_CORE Global build settings / Kernel build options / Enable process core dump support
CONFIG_IPV6 Global build settings / Enable IPv6 support in packages
CONFIG_KERNEL_MAGIC_SYSRQ Global build settings / Kernel build options / Compile the kernel with SysRq support
CONFIG_KERNEL_PRINTK_TIME Global build settings / Kernel build options / Enable printk timestamps
CONFIG_PACKAGE_MAC80211_DEBUGFS Kernel modules / Wireless Drivers / kmod-mac80211 / Export mac80211 internals in DebugFS 21 KB
CONFIG_PACKAGE_MAC80211_MESH Kernel modules / Wireless Drivers / kmod-mac80211 / Enable 802.11s mesh support 29 KB
Options that can be enabled to save space.
Config variable Menu path
CONFIG_STRIP_KERNEL_EXPORTS Global build settings / Strip unnecessary exports from the kernel image
CONFIG_USE_MKLIBS Global build settings / Strip unnecessary functions from libraries
make kernel_menuconfig options that can save space.
Config variable Menu path Comments
CONFIG_SERIAL_8250 Device Drivers / Character devices / Serial drivers / 8250/16550 and compatible serial support This will also save RAM by preventing /sbin/askfirst from running
CONFIG_EARLY_PRINTK Kernel hacking / Early printk
To build a kernel that only works with a specific device, run make kernel_menuconfig CONFIG_TARGET=subtarget to edit target/linux/<platform>/*/config-default and go to Machine selection / <Platform> machine selection and disable all devices except for the specific device. This can save some disk space and RAM.
Increase block size from the default 256 KB to improve compression. Warning: By default 3 blocks will be cached so this will also make the router use more RAM (if 3 blocks are cached, and a block size of 1024 KB is used, this will use 2,304 KB more RAM (3 * 1024 KB - 3 * 256 KB)). It may also make the router use more CPU to decompress the larger blocks.
Config variable Menu path
TARGET_SQUASHFS_BLOCK_SIZE Target Images / squashfs / Block size
Options that can be enabled to save RAM.
Config variable Menu path
PACKAGE_zram-swap Base system
PROCD_ZRAM_TMPFS Base system / procd Configuration
Reduce the number of cached blocks by running make kernel_menuconfig.
Config variable Menu path
CONFIG_SQUASHFS_FRAGMENT_CACHE_SIZE File systems / Miscellaneous filesystems / Additional option for memory-constrained systems / Number of fragments cached