Re: [RFC PATCH v2 00/13] nommu UML

[Hajime Tazaki <thehajime@gmail.com>]

Hello Anton,

thanks for the comment.

On Fri, 15 Nov 2024 19:26:07 +0900,
Anton Ivanov wrote:

> > What do others think? Would you use it? What for?
> 
> I always thought of it as "another LKL". In that case, it can be compared
> to LKL on merit and if it is equivalent or better - go into kernel.
> 
> If there is another use case, I will be glad to hear it.

In a high-level view,

the usage is different (no merit/demerit).
LKL is used with userspace binaries, linked with, or dynamically
replaced with the liblinux.so.  LKL has a userspace API derived from
syscall interface, which can be used to bridge LKL-world and
host-kernel world (not specific to Linux host).

This patchset (nommu UML) doesn't change the usage of current UML.

In an internal implementation point of view,

both (LKL and nommu-UML) uses !MMU.  While LKL can be implemented with
MMU-full configuration, we found (the last patch was back in 2021)
that it is not trivial.

LKL has no process model, currently only runs in a single (LKL)
process.  no vfork(2) support.
nommu-UML can host multiple processes with vfork available.

the patch size is:
LKL (last v8 patch): mostly 5k lines of modifications
nommu-UML: 1.2k lines of mods.


I think it looks like similar (as I'm from LKL which also uses !MMU),
but different from various aspects.

let me know if you wish to see more about the comparison.

-- Hajime