Messages in this thread |  | | Subject | Re: Limited RAM - how to save it? | From | Lars Brinkhoff <> | Date | 06 Nov 2001 07:58:31 +0100 |
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Jan-Benedict Glaw <jbglaw@microdata-pos.de> writes: > I'm working on a 4MB linux system (for a customer) which has quite > limited resources [...] If you've got further ideas on getting the > kernel a bit smaller, would be nice to get a mail dropped...
I started a port of Linux 2.3.99 to a MIPS device which 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. Also, I don't know whether they apply to the current kernels.
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 reduced 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.
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 the product.
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 the 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 <greyham@research.canon.com.au>.
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 long since I worked with this).
text data bss dec hex filename 572128 41964 15860 629952 99cc0 vmlinux
-- Lars Brinkhoff http://lars.nocrew.org/ Linux, GCC, PDP-10 Brinkhoff Consulting http://www.brinkhoff.se/ programming - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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