Re: [PATCH RFC 0/6] NFSD: Pull Read chunks in XDR decoders

["J. Bruce Fields" <bfields@fieldses.org>]

On Tue, Aug 31, 2021 at 03:05:09PM -0400, Chuck Lever wrote:
> Hi Bruce-
> 
> Here is part of what we discussed recently about trying to align
> pages in NFS WRITE requests so that splice can be used. This
> series updates server-side RPC and svcrdma to ensure that an
> aligned xdr_buf::pages array is presented to NFSD, which is then
> converted into an aligned rq_vec for the VFS layer.

Seems sensible to me.

Do you have a git tree?  It didn't apply cleanly to 5.14 when I tried,
but I didn't stop to figure out why.

> The next step would be to look at how to make the best use of the
> aligned rq_vec.

Have you done any performance comparison just with this?

Doesn't seem like it should make a significant difference, but it might
be interesting to check anyway.

--b.

> My naive thought is that where there is a PAGE_SIZE
> entry in rq_vec and there is no page in the file's page cache at
> that offset, the transport-provided page can be flipped into place.
> Might work for replacing whole pages as well, but baby steps first.
> 
> This series has been exercised a bit with both TCP and RDMA, but no
> guarantees that it is completely bug-free. NFSv4 compounds with
> multiple WRITE payloads on RDMA are treated like TCP: the RPC
> message is contained in an unstructured stream of unaligned pages.
> 
> Comments encouraged.
> 
> ---
> 
> Chuck Lever (6):
>       SUNRPC: Capture value of xdr_buf::page_base
>       SUNRPC: xdr_stream_subsegment() must handle non-zero page_bases
>       NFSD: Have legacy NFSD WRITE decoders use xdr_stream_subsegment()
>       SUNRPC: svc_fill_write_vector() must handle non-zero page_bases
>       NFSD: Add a transport hook for pulling argument payloads
>       svcrdma: Pull Read chunks in ->xpo_argument_payload
> 
> 
>  fs/nfsd/nfs3proc.c                       |   3 +-
>  fs/nfsd/nfs3xdr.c                        |  16 +--
>  fs/nfsd/nfs4proc.c                       |   3 +-
>  fs/nfsd/nfs4xdr.c                        |   6 +
>  fs/nfsd/nfsproc.c                        |   3 +-
>  fs/nfsd/nfsxdr.c                         |  13 +--
>  fs/nfsd/xdr.h                            |   2 +-
>  fs/nfsd/xdr3.h                           |   2 +-
>  include/linux/sunrpc/svc.h               |   6 +-
>  include/linux/sunrpc/svc_rdma.h          |   8 ++
>  include/linux/sunrpc/svc_xprt.h          |   3 +
>  include/trace/events/rpcrdma.h           |  26 +++++
>  include/trace/events/sunrpc.h            |  20 +++-
>  net/sunrpc/svc.c                         |  38 +++++--
>  net/sunrpc/svcsock.c                     |   8 ++
>  net/sunrpc/xdr.c                         |  32 +++---
>  net/sunrpc/xprtrdma/svc_rdma_recvfrom.c  |  37 +++++-
>  net/sunrpc/xprtrdma/svc_rdma_rw.c        | 139 ++++++++++++++++++++---
>  net/sunrpc/xprtrdma/svc_rdma_transport.c |   1 +
>  19 files changed, 292 insertions(+), 74 deletions(-)
> 
> --
> Chuck Lever