Re: Execution of pre compiled lua code from memory mapped files

Hi,

On Wed, May 27, 2015 at 12:54 PM, Hans Riekehof <Riekehof@schoeps.de> wrote:

Hi everyone,

i am quite new to lua and i want to execute pre compiled lua code directly from a memory mapped file. The background is this:

I am working in the embedded systems area and as you know memory consumption especially RAM usage is critical. In the system i am currently working on with a small team, there is the nice situation that we have a quite large flash. The uC in this system is capable of executing code directly from flash. From this flash the uC boots a small operating system which includes basic POSIX functionality like file operations etc.
On top of that we also included Lua as a script language based on a implementation from the eLua-project. In the eLua Version, which is Lua 5.1, there is a patch included which should save RAM usage.
I know now that the patch is not working as I expected because the pre compiled modules are still copied into the "package.loaded" table and therefore consume a lot of RAM.

The patch in eLua is designed to let you execute _bytecode_ directly from flash. Right now it doesn't go further than this, so in that respect the patch is doing what's supposed to do. If I'm reading your e-mail right, what you want is the whole module's memory layout to be saved to flash and loaded from there, which might not be doable.

In any case, it would be useful if you opened an issue in the eLua github repository to talk about this.

Thanks,

Bogdan

The best thing would be, if we could execute pre compiled lua code from a memory mapped file. Than we could have a lot of pre compiled lua modules in the flash and work with them without wasting RAM. This feature would also be useful in Linux and Windows. In Linux you could use mmap() in windows there is an equivalent I don't know right now.
I would like to make a feature request on this for some next lua Version :) I think a generic implementation of this would be great in a lot of use cases. It could also be a feature you can activate or deactivate during the compilation of lua. I imagine something like this:

If you call mod = require 'mod' the loader can recognize if mod is in a pre-compiled file which is memory mapable. In Linux this would turn out in a call to mmap() in an embedded system you can
return a pointer with the starting address of the file in memory.
Than you can start using mod as you want but it is not copied into the lua state.

If there is another way or if you have other ideas how to save RAM in a lua sate please tell me.

Best regards,
Hans