Re: [PATCH V10 00/10] famfs: port into fuse

[John Groves]

On 26/04/14 03:19PM, Miklos Szeredi wrote:
> On Fri, 10 Apr 2026 at 21:44, Joanne Koong <joannelkoong@xxxxxxxxx> wrote:
> 
> > Overall, my intention with bringing this up is just to make sure we're
> > at least aware of this alternative before anything is merged and
> > permanent. If Miklos and you think we should land this series, then
> > I'm on board with that.
> 
> TBH, I'd prefer not to add the famfs specific mapping interface if not
> absolutely necessary.  This was the main sticking point originally,
> but there seemed to be no better alternative.
> 
> However with the bpf approach this would be gone, which is great.
> 
> So let us please at least have a try at this. I'm not into bpf yet,
> but willing to learn.
> 
> Thanks,
> Miklos

Thanks for responding...

My short response: Noooooooooo!!!!!!

I very strongly object to making this a prerequisite to merging. This
is an untested idea that will certainly delay us by at least a couple
of merge windows when products are shipping now, and the existing approach
has been in circulation for a long time. It is TOO LATE!!!!!!

Famfs is not a science project, it's enablement for actual products and
early versions are available now!!!

That doesn't mean we couldn't convert later IF THERE ARE NO HIDDEN PROBLEMS.

What are the risks of converting to BPF?

- I don't know how to do it - so it'll be slow (kinda like my fuse learning
  curve cost about a year because this is not that similar to anything
  else that was already in fuse.

- Those of us who are involved don't fully understand either the security
  or performance implications of this. It 

- Famfs is enabling access to memory and mapping fault handling must be
  at "memory speed". We know that BPF walks some data structures when a 
  program executes. That exposes us to additional serialized L3 cache 
  misses each time we service a mapping fault (any TLB & page table miss).
  This should be studied side-by-side with the existing approach under
  multiple loads before being adopted for production.

- This has never been done in production, and we're throwing it in the way
  of a project that has been soaking for years and needs to support early
  shipments of products.

If this is the only path, I'd like to revive famfs as a standalone file
system. I'm still maintaining that and it's still in use.

Please reconsider Miklos. To use an American football metaphor, this moves
the goal posts by a mile, and that's not reasonable!!!

Thanks,
John