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Subject: Re: [PATCH v2 2/6] xprtrdma: Simplify rpcrdma_convert_kvec() and
 frwr_map()
To:     Chuck Lever <chuck.lever@oracle.com>, linux-nfs@vger.kernel.org,
        linux-rdma@vger.kernel.org
References: <161236925476.1030487.10407536259816633879.stgit@manet.1015granger.net>
 <161236944071.1030487.460353530274045763.stgit@manet.1015granger.net>
From:   Tom Talpey <tom@talpey.com>
Message-ID: <a26eed70-3f0f-907e-3c88-1b5f949c950c@talpey.com>
Date:   Wed, 3 Feb 2021 13:07:54 -0500
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Reviewed-By: Tom Talpey <tom@talpey.com>

On 2/3/2021 11:24 AM, Chuck Lever wrote:
> Clean up.
> 
> Remove a conditional branch from the SGL set-up loop in frwr_map():
> Instead of using either sg_set_page() or sg_set_buf(), initialize
> the mr_page field properly when rpcrdma_convert_kvec() converts the
> kvec to an SGL entry. frwr_map() can then invoke sg_set_page()
> unconditionally.
> 
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>   net/sunrpc/xprtrdma/frwr_ops.c  |   12 ++++--------
>   net/sunrpc/xprtrdma/rpc_rdma.c  |    2 +-
>   net/sunrpc/xprtrdma/xprt_rdma.h |    9 +++++----
>   3 files changed, 10 insertions(+), 13 deletions(-)
> 
> diff --git a/net/sunrpc/xprtrdma/frwr_ops.c b/net/sunrpc/xprtrdma/frwr_ops.c
> index baca49fe83af..13a50f77dddb 100644
> --- a/net/sunrpc/xprtrdma/frwr_ops.c
> +++ b/net/sunrpc/xprtrdma/frwr_ops.c
> @@ -306,14 +306,10 @@ struct rpcrdma_mr_seg *frwr_map(struct rpcrdma_xprt *r_xprt,
>   	if (nsegs > ep->re_max_fr_depth)
>   		nsegs = ep->re_max_fr_depth;
>   	for (i = 0; i < nsegs;) {
> -		if (seg->mr_page)
> -			sg_set_page(&mr->mr_sg[i],
> -				    seg->mr_page,
> -				    seg->mr_len,
> -				    offset_in_page(seg->mr_offset));
> -		else
> -			sg_set_buf(&mr->mr_sg[i], seg->mr_offset,
> -				   seg->mr_len);
> +		sg_set_page(&mr->mr_sg[i],
> +			    seg->mr_page,
> +			    seg->mr_len,
> +			    offset_in_page(seg->mr_offset));
>   
>   		++seg;
>   		++i;
> diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
> index 832765f3ebba..529adb6ad4db 100644
> --- a/net/sunrpc/xprtrdma/rpc_rdma.c
> +++ b/net/sunrpc/xprtrdma/rpc_rdma.c
> @@ -214,7 +214,7 @@ rpcrdma_convert_kvec(struct kvec *vec, struct rpcrdma_mr_seg *seg,
>   		     unsigned int *n)
>   {
>   	if (vec->iov_len) {
> -		seg->mr_page = NULL;
> +		seg->mr_page = virt_to_page(vec->iov_base);
>   		seg->mr_offset = vec->iov_base;
>   		seg->mr_len = vec->iov_len;
>   		++seg;
> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
> index 94b28657aeeb..02971e183989 100644
> --- a/net/sunrpc/xprtrdma/xprt_rdma.h
> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
> @@ -283,10 +283,11 @@ enum {
>   				  RPCRDMA_MAX_IOV_SEGS,
>   };
>   
> -struct rpcrdma_mr_seg {		/* chunk descriptors */
> -	u32		mr_len;		/* length of chunk or segment */
> -	struct page	*mr_page;	/* owning page, if any */
> -	char		*mr_offset;	/* kva if no page, else offset */
> +/* Arguments for DMA mapping and registration */
> +struct rpcrdma_mr_seg {
> +	u32		mr_len;		/* length of segment */
> +	struct page	*mr_page;	/* underlying struct page */
> +	char		*mr_offset;	/* IN: page offset, OUT: iova */
>   };
>   
>   /* The Send SGE array is provisioned to send a maximum size
> 
> 
>