Re: [PATCH v1 10/10] svcrdma: Handle additional inline content

[Sagi Grimberg <sagig@dev.mellanox.co.il>]

On 1/9/2015 9:23 PM, Chuck Lever wrote:
> Most NFS RPCs place large payload arguments at the end of the RPC
> header (eg, NFSv3 WRITE). For NFSv3 WRITE and SYMLINK, RPC/RDMA
> sends the complete RPC header inline, and the payload argument in a
> read list.
>
> One important case is not like this, however. NFSv4 WRITE compounds
> can have an operation after the WRITE operation. The proper way to
> convey an NFSv4 WRITE is to place the GETATTR inline, but _after_
> the read list position. (Note Linux clients currently do not do
> this, but they will be changed to do it in the future).
>
> The receiver could put trailing inline content in the XDR tail
> buffer. But the Linux server's NFSv4 compound processing does not
> consider the XDR tail buffer.
>
> So, move trailing inline content to the end of the page list. This
> presents the incoming compound to upper layers the same way the
> socket code does.
>

Would this memcpy be saved if you just posted a larger receive buffer
and the client would used it "really inline" as part of it's post_send?

I'm just trying to understand if this complicated logic is worth the
extra bytes of a larger recv buffer you are saving...

Will this code path happen a lot? If so you might get some overhead
you may want to avoid.

I may not see the full picture here... Just thought I'd ask...

Sagi.