Kernel memory usage optimisations?

Kernel memory usage optimisations?

[Marko Kenttälä]

Hi,

I'm working on a project that uses Linux kernel version 2.4.16 on an 
embedded ARM device. Since we have limited memory (both RAM and Flash) I 
have tuned down some kernel internal defines to make it use less memory:

include/linux/major.h: MAX_CHRDEV 255->20, MAX_BLKDEV 255->10
include/linux/tty.h: MAX_NR_CONSOLES 63->3, MAX_NR_USER_CONSOLES 63->3
include/linux/kernel-stat.h: DK_MAX_MAJOR 16->4, DK_MAX_DISK 16->4
include/linux/sched.c: PIDHASH_SZ 1024->16
include/linux/tty.h: NR_PTYS 256->16, NR_LDISCS 16->4
kernel/printk.c: LOG_BUF_LEN 16384->2048

With these I have saved about 100 KB from bss. Do you see any dangerous 
side-effects in those modifications?

I understand that best area for saving memory usage is the C-library but 
are there any other kernel areas? I'm thinking of dropping swapfile support 
and maybe some other subsystems that are not needed in embedded device.

--
Marko Kenttälä, Software Engineer
TERAFLOPS Ltd., Member of Elektrobit Group
Mobile: +358 40 7501832, Fax: +358 3 2258484
http://www.teraflops.com, http://www.elektrobit.com

Re: Kernel memory usage optimisations?

[Anton Blanchard]

 
> I understand that best area for saving memory usage is the C-library but 
> are there any other kernel areas? I'm thinking of dropping swapfile support 
> and maybe some other subsystems that are not needed in embedded device.

Check out all the cacheline_aligned usage, in all the cases I could see
there was no reason to do this on a UP machine. You could probably get
away with redefining them to do nothing.

Also you could drop the sizes of the hashes (dentry, inode, mount,
buffer, page, route) if they are taking up RAM.

Anton

Re: Kernel memory usage optimisations?

[David Woodhouse]

marko.kenttala@teraflops.com said:
>  I understand that best area for saving memory usage is the C-library
> but  are there any other kernel areas? I'm thinking of dropping
> swapfile support  and maybe some other subsystems that are not needed
> in embedded device. 

You could potentially remove block device support altogether.

--
dwmw2