Re: [MirageOS-devel] Mirage and piÃata numbers

[Anil Madhavapeddy <anil@xxxxxxxxxx>]

On 2 Jul 2015, at 14:02, Hannes Mehnert <hannes@xxxxxxxxxxx> wrote:
> 
> Amir,
> 
> On 07/02/2015 13:31, Amir Chaudhry wrote:
>> - Could Hannes or David tell me the size of the PiÃata and its equivalent in 
>> the traditional stack? (I already have a comparison in kloc but I'm curious 
>> about the deployed image). 
> 
> binary size is 8.2M (mostly cow it seems, compressed 1.4MB). traditional
> stacks: not sure, maybe 200MB?

Incidentally, I posted a few things that we could do to reduce the binary size 
further to HN and forgot to mirror it here 
https://news.ycombinator.com/item?id=9800063

- Native code compilation still includes symbols. Stripping that reduces the 
size at the obvious cost of debugging ease.

- When an OCaml module is touched for a single function, the entire module is 
included at present. OCaml 4.02.0 included module aliases to make it easier to 
break down module hierarchies into less monolithic chunks. They work by 
exposing module equivalence in the signature, and reduced the size of Unix 
binaries in Jane Street Core by 90% in some cases; 
https://blogs.janestreet.com/better-namespaces-through-module-aliases/

- Bytecode (while less performant) can be compressed more easily than native 
code. We've had DNS and OpenFlow servers that are less than a megabyte in size 
quite easily when compiled with bytecode.

- Dead code elimination requires some whole program optimisation, and currently 
only works with bytecode via the OCamlClean tool: 
http://www.algo-prog.info/ocaml_for_pic/web/index.php?id=ocamlclean .

Porting this to native code is on the TODO list, but needs some fiddling with 
frame pointers in the generated binaries to do a good job. 

So the overall message is that reducing the deployed binary size is now a 
compiler problem, since the unikernel architecture lets us provide it with much 
more information (configuration files and OS libraries as well as the 
application logic).

-anil
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