Re: [MirageOS-devel] Size of MirageOS, too big now?

[Hiroshi Doyu <hiroshi.doyu@xxxxxxxxxxxx>]

Hello Anil,

Recently Linux *kernel*(IoT for Linux, IoTL) has been being shrunk
around 1MB runtime RAM and its minimal system can run with a few MB of
RAM[1]. So it would be nice if "MirageOS with UDP stack" runs with
smaller RAM than IoTL, probably around 1MB?

Yesterday, I found the following. Quite close to the above ~1MB target
with '-use-lto':

~/src/mirage-skeleton/device-usage/network$ du -h network.hvt 
1.6M    network.hvt

Doesn't bytecode require runtime(ocamlrun?) installed too?

$ objdump -b binary -s hello.byte | head -7
 0000 23212f68 6f6d652f 65686972 646f792f  #!/home/ehirdoy/
 0010 2e6f7061 6d2f342e 30362e31 2f62696e  .opam/4.06.1/bin
 0020 2f6f6361 6d6c7275 6e0a5400 0000df02  /ocamlrun.T.....

$ strip -s ocamlrun && du -h ocamlrun # dynamically linked, though....
268K    ocamlrun

So you suggested to use native code. As far as I understand, '-use-lto' 
option stripped off unused modules. It's quite nice. Is there any
ocamlclean(stripping off unused functions?) for native? Because
MirageOS is statically linked, there's no point to have unused
functions in it(?)

[1] https://schd.ws/hosted_files/elciotna18/67/opdenacker-size-bof.pdf

Thanks!!

On Wed, 2019-02-13 at 10:25 -0800, Anil Madhavapeddy wrote:
> From a quick look at the symbol map, I suspect that moving the OS
> module
> to module aliases and Dune virtual_modules will help eliminate some
> hard
> dependencies.  The 500KB->960KB isn’t too far off the mark; there are
> links
> to Ipaddr and Lwt that would account for the increase.
> 
> It would be helpful to know what you’re aiming for — as small as
> possible
> without a performance hit? Bytecode (as we experimented with in the
> ASPLOS
> paper) is very slow for production use, and so hasn’t been maintained
> in
> ocaml-freestanding.  For native, how small is small enough for your
> purposes?
> 
> best,
> Anil
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