Re: need SUNRPC TCP to receive into aligned pages [was: Re: [PATCH 1/6] NFSD: add the ability to enable use of RWF_DONTCACHE for all IO]

[Mike Snitzer <snitzer@kernel.org>]

On Thu, Jun 12, 2025 at 11:58:27AM -0400, Chuck Lever wrote:
> On 6/12/25 11:56 AM, Mike Snitzer wrote:
> > On Thu, Jun 12, 2025 at 10:17:22AM -0400, Benjamin Coddington wrote:
> >>
> >> What's already been mentioned elsewhere, but not yet here:
> >>
> >> The transmitter could always just tell the receiver where the data is, we'd
> >> need an NFS v3.1 and an extension for v4.2?
> >>
> >> Pot Stirred,
> >> Ben
> > 
> > Yeah, forgot to mention giving serious consideration to extending
> > specs to make this happen easier.  Pros and cons to doing so.
> > 
> > Thanks for raising it.
> > 
> > Mike
> 
> NFS/RDMA does this already. Let's not re-invent the wheel.

TCP is ubiquitous, I know you seem to really not want us to seriously
pursue fixing/improving things to allow for the WRITE payload to be
stored in an aligned buffer that allows zero-copy but... the value of
not requiring any RDMA hardware or client changes is too compelling to
ignore.

RDMA either requires specialized hardware or software (soft-iwarp or
soft-roce). 

Imposing those as requirements isn't going to be viable for a large
portion of existing deployments.