So hashing out details of pNFS layout isn't interesting to many people.
But if you want a broader architectural discussion about how to overcome
issues (and what those issues actually are) with the use of persistent
memory for NAS, then that may be interesting. So what do you actually want?
I mentioned pNFS briefly only as an example. There have
been a variety of proposals and approaches so far, and
it's time, I believe, to start focusing our efforts.
Thus I'm requesting a "broader architectural discussion
about how to overcome issues with the use of persistent
memory for NAS," in particular how we'd like to do this
with the Linux implementations of the iSER, SRP, and
NFS/RDMA protocols using DAX/pmem or NVM[ef].
I agree,
I anticipate that we'll gradually see more and more implementations
optimizing remote storage access in the presence of pmem devices (maybe
even not only RDMA?). The straight forward approach would be for each
implementation to have it's own logic for accessing remote pmem
devices but I think we have a chance to consolidate that in a single
API for everyone.
I think the most natural way to start is NFS/RDMA (SCSI would be a bit
more challenging...)
It is not going to be like the well-worn paradigm that
involves a page cache on the storage target backed by
slow I/O operations. The protocol layers on storage
targets need a way to discover memory addresses of
persistent memory that will be used as source/sink
buffers for RDMA operations.
And making data durable after a write is going to need
some thought. So I believe some new plumbing will be
necessary.
The challenge here is persistence semantics that are missing in
today's HCAs, so I think we should aim to have a SW solution for
remote persistence semantics with sufficient hooks for possible
HW that might be able to have it in the future...
I know this is not everyone's cup of tea. A BoF would
be fine, if the PC believes that is a better venue (and
I'm kind of leaning that way myself).
I'd be happy to join such a discussion.
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