Re: [RFC net-next 0/7] Provide an ism layer

Niklas Schnelle
2025-01-17T10:38:55Z

On Fri, 2025-01-17 at 10:13 +0800, Dust Li wrote:
> >
---8<---
> > Here are some of my thoughts on the matter:
> > > >
> > > > Naming and Structure: I suggest we refer to it as SHD (Shared Memory
> > > > Device) instead of ISM (Internal Shared Memory).
> >
> >
> > So where does the 'H' come from? If you want to call it Shared Memory _D_evice?
>
> Oh, I was trying to refer to SHM(Share memory file in the userspace, see man
> shm_open(3)). SMD is also OK.
>
> >
> >
> > To my knowledge, a
> > > > "Shared Memory Device" better encapsulates the functionality we're
> > > > aiming to implement.
> >
> >
> > Could you explain why that would be better?
> > 'Internal Shared Memory' is supposed to be a bit of a counterpart to the
> > Remote 'R' in RoCE. Not the greatest name, but it is used already by our ISM
> > devices and by ism_loopback. So what is the benefit in changing it?
>
> I believe that if we are going to separate and refine the code, and add
> a common subsystem, we should choose the most appropriate name.
>
> In my opinion, "ISM" doesn’t quite capture what the device provides.
> Since we’re adding a "Device" that enables different entities (such as
> processes or VMs) to perform shared memory communication, I think a more
> fitting name would be better. If you have any alternative suggestions,
> I’m open to them.

I kept thinking about this a bit and I'd like to propose yet another
name for this group of devices: Memory Communication Devices (MCD)

One important point I see is that there is a bit of a misnomer in the
existing ISM name in that our ISM device does in fact *not* share
memory in the common sense of the "shared memory" wording. Instead it
copies data between partitions of memory that share a common
cache/memory hierarchy while not sharing the memory itself. loopback-
ism and a possibly future virtio-ism on the other hand would share
memory in the "shared memory" sense. Though I'd very much hope they
will retain a copy mode to allow use in partition scenarios.

With that background I think the common denominator between them and
the main idea behind ISM is that they facilitate communication via
memory buffers and very simple and reliable copy/share operations. I
think this would also capture our planned use-case of devices (TTYs,
block devices, framebuffers + HID etc) provided by a peer on top of
such a memory communication device.

Thanks,
Niklas