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

Christoph Hellwig
2026-04-17T08:13:51Z

On Thu, Apr 16, 2026 at 03:43:31PM -0700, Darrick J. Wong wrote:
> ...the memory interleaving is a rather interesting quality of famfs.
> There's no good way to express a formulaic meta-mapping in traditional
> iomap parlance, and famfs needs that to interleave across memory
> controllers/dimm boxen/whatever. Throwing individual iomaps at the
> kernel is a very inefficient way to do that. So I don't think there's a
> good reason to get rid of GET_FMAP at this time...

Why no? We can triviall make an iomap point to multiple backing
devices and throw in a stride/offset. That would make btrfs
striping (and non-degraded parity RAID reads) a lot more efficient.

> ...however the strongest case (IMO) would be if (having merged famfs) we
> then merge fuse-iomap after famfs. Then we extend the existing
> fuse-iomap-bpf prototype to allow per-mount and per-inode iomap bpf ops.
> That enables us to analyze thoroughly the performance characteristics of:

Don't go there. I think that you two are comining up with two
interfaces for roughly the same thing is a pretty clear indicator
that this needs to be fully hashed out as a single interface first,
and any kind of preliminary merging is just going to create problems.