Re: [PATCH v9 08/12] NFSD: Simplify nfsd_iov_iter_aligned_bvec()

[Mike Snitzer <snitzer@kernel.org>]

On Mon, Nov 03, 2025 at 11:53:47AM -0500, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
> 
> Pages in the RPC receive buffer are contiguous. Practically
> speaking, this means that, after the first bvec, the bv_offset
> field is always zero.
> 
> The loop in nfsd_iov_iter_aligned_bvec() also sets "skip" to zero
> after the first bvec is checked. Thus, for bvecs following the first
> one, bv_offset = 0 and skip = 0, and the check becomes:
> 
>   (0 + 0) & addr_mask = 0
> 
> This always passes regardless of the alignment mask.
> 
> Since all bvecs after the first one start at bv_offset zero (page-
> aligned), they are inherently aligned for DIO. Therefore, only the
> first bvec needs to be checked for DIO alignment.
> 
> Note that for RDMA transports, the incoming payload always starts on
> page alignment, since svcrdma sets up the RDMA Read sink buffers
> that way. For RDMA, this loop visits every bvec in each payload, and
> never finds an unaligned bvec.
> 
> Reviewed-by: Jeff Layton <jlayton@kernel.org>
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

Very welcome improvement!

Reviewed-by: Mike Snitzer <snitzer@kernel.org>