Re: [PATCH] Stem compression for kallsyms

[Rusty Russell <rusty@rustcorp.com.au>]

In message <20021224011227.GA3171@averell> you write:
> 
> This patch implements simple stem compression for the kallsyms symbol 
> table. Each symbol has as first byte a count on how many characters
> are identical to the previous symbol. This compresses the often
> common repetive prefixes (like subsys_) fairly effectively.
> 
> On a fairly full featured monolithic i386 kernel this saves about 60k in 
> the kallsyms symbol table.
> 
> The changes are very simple, so the 60k are not shabby.
> 
> One visible change is that the caller of kallsyms_lookup has to pass in 
> a buffer now, because it has to be modified. I added an arbitary
> 127 character limit to it.
> 
> Still >210k left in the symbol table unfortunately. Another idea would be to 
> delta encode the addresses in 16bits (functions are all likely to be smaller 
> than 64K).  This would especially help on 64bit hosts. Not done yet, however.
> 
> No, before someone asks, I don't want to use zlib for that. Far too fragile 
> during an oops and overkill too and it would require to link it into all
> kernels.

Hi Andi,

	For the IDE oopser, I used the 16-bit size trick and a very
simple static huffman encoding, which IIRC brought the size down to
~100k (I can't find numbers at the moment).  I relied on a linked-list
of tables (for things which were more than 16 bits apart), which is
not such a great idea for the kallsyms table.  Maybe eliminate
aliases, and then use a 0 size to prefix a full new pointer?

Anyway, here's the post if you're interested:
	http://www.uwsg.iu.edu/hypermail/linux/kernel/0209.2/0062.html

Cheers,
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.