The following message is a courtesy copy of an article
that has been posted to
comp.os.linux.development.system,comp.os.linux.misc,comp.os.linux.advocacy as well.
*** I'd be very interested in hearing about work done by others ***
*** to reduce the size of Linux. I already know about Graham ***
*** Stoney's CONFIG_MESSAGES and dead function optimisation ***
*** patches. ***
Wallace Owen wrote:
> Can anyone tell me what files in the Linux kernel have data
> declarations whose dimensions can be safely reduced? My efforts
> at producing a small kernel have got the code segment down below
> half a meg, but the data segment is 1.5 megabytes.
I started a port of Linux 2.3.99 to our MIPS R3000-ish device (IDT
RC32064, really). This device usually has 2M flash and 4M RAM.
To reduce the size of the text and data sections, I sorted the output
of the "size" command and investigated the files with the largest
sections.
These are the memory-saving changes I arrived at. They are not really
tested, so some of them may break some functionality.
fs/dcache.c
Changed HASH_BITS from 14 to 8. This reduces the size of the
cache from 128K to 2K.
fs/inode.c
Changed HASH_BITS from 14 to 8. This reduces the size of the
cache from 128K to 2K.
include/linux/blk.h
Changed NR_REQUEST from 256 to 16. This reduces the number of
requests that can be queued. The size of the queue is reduce
from 16K to 1K.
include/linux/major.h
Changed MAX_BLKDEV and MAX_CHRDEV from 256 to 10 and 20,
respectively. This reduces the number of block and character
devices and saves about 40K.
kernel/printk.c
Changed LOG_BUF_LEN from 16384 bytes to 2048 bytes.
include/linux/tty.h
Changed NR_PTYS and NR_LDISCS from 256 and 16, respectively,
to 16 and 4, respectively. Saved about 12K.
Warning: this change may break the pty driver, in which
case further modifications will have to be done to
drivers/char/pty.c.
kernel/panic.c
Changed a buffer from 1024 bytes to 200 bytes.
include/linux/sched.h
Changed PIDHASH_SZ from 1024 to 16, which saves
1008 bytes.
arch/mips/kernel/entry.S
(Has 21184 bytes of data which might be trimmed?)
include/linux/mmzone.h
NR_GPFINDEX from 0x100 to 0x10. Saves 4800 bytes,
but I'm not sure it doesn't break anything.
net/Makefile, net/socket.c, net/nosocket.c
Replacing socket.c with nosocket.c, a file containing
dummy replacement functions for those in socket.c, saves
about 24K.
Warning: this disables the socket API entirely, but it
is currently not used in our product.
net/Makefile, net/network.a, net/core
Excluding net/core/core.o from net/network.a doesn't save
anything. I guess core.o isn't referenced by anything
in the rest of the kernel (except maybe socket.c, see
above).
mm/Makefile, mm/swapfile.c, mm/swap_state.c, mm/noswapfile.c, mm/noswap_state.c
Replacing swapfile.c with noswapfile.c, and swap_state.c with
noswap_state.c saves about 12K. The no*.c files contains empty
replacement functions.
Warning: this disables swapping of anonymous memory, which isn't
used in our product. But note that demand paging of executables
still works.
mm/Makefile, mm/mmap.c
The functions in mmap.c could probably also be replaced by
empty functions. Estimated saving: 9K (not included in the
grand total below).
*, CONFIG_MESSAGES
Applying the CONFIG_MESSAGES patch and disabling all
kernel messages saves about 80K.
The CONFIG_MESSAGES patch was written by Graham Stoney
<[EMAIL PROTECTED]>.
With all of the above, and only this enabled in .config:
CONFIG_EXPERIMENTAL=y
CONFIG_CPU_R3000=y
CONFIG_CPU_LITTLE_ENDIAN=y
CONFIG_ELF_KERNEL=y
CONFIG_BINFMT_ELF=y
CONFIG_MODULES=y
CONFIG_MODVERSIONS=y
CONFIG_KMOD=y
CONFIG_CROSSCOMPILE=y
, the kernel is down to about 550K.
Here is the output of "size vmlinux". I think this is without the
CONFIG_MESSAGES patch (it was many months since I worked with this).
text data bss dec hex filename
572128 41964 15860 629952 99cc0 vmlinux
--
To unsubscribe from this list, send a message to [EMAIL PROTECTED]
with the command "unsubscribe linux-embedded" in the message body.
For more information, see <http://waste.org/mail/linux-embedded>.
