Paul Gortmaker
Paul.Gortmaker@anu.edu.au
Most of these patches are against the current 1.2.x kernel, as it is a bit smaller than the 1.3.x kernels to begin with. If you are tight on memory, you are best to run the latest 1.2.x kernel as opposed to the latest 1.3.x development series.
The RAM Disk
The "old" Disk Driver
The Modules Code
The Old init Code
The Serial Driver
The Floppy Driver
The ne2000 Driver
The 3c503 Driver
The SCSI Blacklist
The printk() Ring Buffer
The Kswap Patches
Removing IBM ThinkPad Support
The `-m386' GCC option
As a more drastic alternative, you can `downgrade' to a 1.0.9 kernel. For those that can't recall, this was the last (i.e. stable) release of the 1.0 series before starting the 1.1 development series. As a quick test, I compiled a 1.0.9 kernel `out of the box' to see how it compared memorywise against my trimmed 1.2.13 kernel. It beat it hands down! For my config, the trimmed 1.2.13 kernel weighed in at 512k code and 148kB data. The stock 1.0.9 kernel with the same config weighed in at a mere 388kB code and 168kB data. I then quickly applied by hand some of the above list (ram / modules / init / serial / ne2k / printk) and had it down to a lean-n-mean 384kB code and 152kB data!! That is a 104kB saving over the trimmed 1.2.13 kernel. This is an excellent kernel to run on 4MB machines. Here is a patch against the 1.0.9 tree that incorporates the above five from the list. Note that some (such as the Thinkpad hack or the reduced hd driver) don't apply to the 1.0.9 kernels, as they weren't in there yet to begin with, so there is nothing to `fix' so to speak.
ramdisk.c is not even
compiled unless you select ramdisk support.
This should be another small memory saving that will help low memory
machines.
ide.c now uses
all the IDE specific features in addition to the standard ST-506 hard
disk specification, the old
disk driver may as well return to its original featureless ST-506 form.
This will be a good choice for users with MFM/RLL or ESDI drives that
can use the memory savings a lot more than the IDE features. Users that
don't wish to use the extended features of their IDE drive(s) can also
use this patch as well. There should be no risk in using this patch,
as all it mainly does is remove code that is IDE specific. I have
tested it in a two drive IDE system and a one drive MFM system.
Just compare the compiled sizes of hd.c with my patch, hd.c without my
patch, and ide.c as seen below, for 1.3.14. (This also doesn't account
for the extra 1/2kB per IDE drive that was dynamically allocated to
to store the IDE drive information.)
# size drivers/block/hd.o.patched
text data bss dec hex
5440 2228 4 7672 1df8
# size drivers/block/hd.o.orig
text data bss dec hex
8992 2324 48 11364 2c64
# size drivers/block/ide.o
text data bss dec hex
17992 4488 96 22576 5830
The "low-fat-diet" hard disk driver is available for v1.2.12 kernels.
``#ifdef CONFIG_MODULES'' and adding it as
a make config option. Note that this patch is for 1.2.x kernels.
I will eventually update it for the 1.3.x kernels.
For those who were complaining about the modules stuff adding bloat, it can be pulled out quite easily. A big win is dumping modules.c, ksyms.c and a good chunk of scsi.c for loading and unloading host adaptors. Also gone are (un)register_netdev, unregister_filesystem and (un)register_binfmt. Note that you *can't* dump register_fiesystem, (un)register_blkdev and (un)register_chrdev because these are also used by non-modules. (However, this could be easily changed...) Of course /proc/ksyms and /proc/modules disappear as well.
The only files that didn't include <linux/config.h>
already were scsi.c
and modules.c (ironic huh?) Of course the module syscalls are still
listed in unistd.h and entry.S, but they are just dummies that
return -ENOSYS like those in kernel/sys.c, so that running insmod on
a non-module kernel doesn't do anything silly. Hopefully this can
go into 1.3.x someday.
drivers/char/serial.c there is a large table of
possible serial devices called rs_table. This table
has 37 entries. You can safely delete all but the ones you are
using, that being the top two, or four if you have four serial
ports installed. (Thanks to Alan Cox for mentioning this one.)
drivers/net/ne.c that will get rid of a large table of
non-conforming cards, and its associated code. If you don't have
a "bad clone" you can just delete or comment out the line that says
#define CONFIG_NE_BAD_CLONES
This patch for the 1.2.x series kernels just #ifdef's out all the PIO code based on whether you have defined CONFIG_EL2_PIO, for a 20% reduction in the driver size, as seen below.
With PIO support:
text data bss dec hex
3576 44 0 3620 e24
-rw------- 1 root root 4964 Apr 13 19:50 3c503.o
Without PIO support:
text data bss dec hex
2700 44 0 2744 ab8
-rw------- 1 root root 4005 Apr 15 15:33 3c503.o
drivers/scsi/scsi.c.
You can cut this device_list down to just the
NULL entry at the end if you don't have any of these devices, or if you
configured your kernel to only ask about LUN #1.
printk() routine uses a 4kB static ring buffer to store
kernel messages in while waiting for klogd() to read them.
The only time this many unread messages pile up is at boot before
klogd() is started. But you can read those by using the
Shift+Page_Up key sequence. You can go into kernel/printk.c
and change the #define LOG_BUF_LEN 4096 to a smaller value
like 512, for a saving of 3.5kB. This will still leave room for over
six full (80 character) lines of kernel messages to be buffered.
There is also a 1kB buffer ("buf") allocated to deal with the incoming
data passed in with a printk() call. No single printk() calls in the kernel
are so huge (or broken) as to dump a whole kB in a single call, and so you
can cut this back to 256 bytes, which is still the equivalent of more
than three full lines of text. (You could allocate this buffer
dynamically with kmalloc(), but things will get ugly if you run out of
memory, and then try to do allocate a buffer so you can do a
printk("Out of memory\n");!!!)
Stephen's latest version of his kswap patches can be found here.