Re: [PATCH 02/11] svcrdma: Use RPC reply map for RDMA_WRITE processing

[Tom Tucker <tom@xxxxxxxxxxxxxxxxxxxxx>]

J. Bruce Fields wrote:
> On Thu, May 29, 2008 at 12:54:47PM -0500, Tom Tucker wrote:
>   
> > Use the new svc_rdma_req_map data type for mapping the client side memory
> > to the server side memory. Move the DMA mapping to the context pointed to
> > by each WR individually so that it is unmapped after the WR completes.
> >
> > Signed-off-by: Tom Tucker <tom@xxxxxxxxxxxxxxxxxxxxx>
> >
> > ---
> >  net/sunrpc/xprtrdma/svc_rdma_sendto.c    |  122 ++++++++++++++----------------
> >  net/sunrpc/xprtrdma/svc_rdma_transport.c |    5 +-
> >  2 files changed, 62 insertions(+), 65 deletions(-)
> >
> > diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
> > index fb82b1b..7cd65b7 100644
> > --- a/net/sunrpc/xprtrdma/svc_rdma_sendto.c
> > +++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
> > @@ -64,10 +64,9 @@
> >   * SGE[sge_count-1]    data from xdr->tail.
> >   *
> >   */
> > -static struct ib_sge *xdr_to_sge(struct svcxprt_rdma *xprt,
> > -				 struct xdr_buf *xdr,
> > -				 struct ib_sge *sge,
> > -				 int *sge_count)
> > +static void xdr_to_sge(struct svcxprt_rdma *xprt,
> > +		       struct xdr_buf *xdr,
> > +		       struct svc_rdma_req_map *vec)
> >  {
> >  	/* Max we need is the length of the XDR / pagesize + one for
> >  	 * head + one for tail + one for RPCRDMA header
> > @@ -84,14 +83,10 @@ static struct ib_sge *xdr_to_sge(struct svcxprt_rdma *xprt,
> >  	sge_no = 1;
> >     
>
> Should the arrays in the svc_rdma_req_map actually be size
> RPC_SVC_MAXPAGES+1 to allow for the RPCRDMA header?
>
>   
Actually, upon further inspection, this is not a bug. The 
RPCSVC_MAXPAGES is used to size the rqstp
page array. This array includes a page for the request hdr, reply hdr 
and one extra page for alignment. For
our use case, the reply hdr page covers the RDMA header.

However, I think this payload length should be clamped in a different 
way. It seems silly to allocate these
things to handle big-data mounts that are rarely used in practice. I 
think it's better to have a transport max
that is more reasonable by default and a module parameter that is 
configurable if you're looking to do big-data
mounts.

Thoughts?
> Also, the only caller of xdr_to_sge() appears to be svc_rdma_sendto(),
> which is called from svc_sendto() immediately after setting:
>
> 	xb = &rqstp->rq_res;
> 	xb->len = xb->head[0].iov_len + 
> 		xb->page_len +
> 		xb->tail[0].iov_len;
>
> So I think xdr_to_sge() is doing a bunch of unnecessary work to handle
> the case where xdr->len could be less than that sum?
>
>   
> >  
> >  	/* Head SGE */
> > -	sge[sge_no].addr = ib_dma_map_single(xprt->sc_cm_id->device,
> > -					     xdr->head[0].iov_base,
> > -					     xdr->head[0].iov_len,
> > -					     DMA_TO_DEVICE);
> > +	vec->sge[sge_no].iov_base = xdr->head[0].iov_base;
> >  	sge_bytes = min_t(u32, byte_count, xdr->head[0].iov_len);
> >  	byte_count -= sge_bytes;
> > -	sge[sge_no].length = sge_bytes;
> > -	sge[sge_no].lkey = xprt->sc_phys_mr->lkey;
> > +	vec->sge[sge_no].iov_len = sge_bytes;
> >  	sge_no++;
> >  
> >  	/* pages SGE */
> > @@ -99,16 +94,13 @@ static struct ib_sge *xdr_to_sge(struct svcxprt_rdma *xprt,
> >  	page_bytes = xdr->page_len;
> >  	page_off = xdr->page_base;
> >  	while (byte_count && page_bytes) {
> > +		vec->sge[sge_no].iov_base =
> > +			page_address(xdr->pages[page_no]) + page_off;
> >  		sge_bytes = min_t(u32, byte_count, (PAGE_SIZE-page_off));
> > -		sge[sge_no].addr =
> > -			ib_dma_map_page(xprt->sc_cm_id->device,
> > -					xdr->pages[page_no], page_off,
> > -					sge_bytes, DMA_TO_DEVICE);
> >  		sge_bytes = min(sge_bytes, page_bytes);
> >  		byte_count -= sge_bytes;
> >  		page_bytes -= sge_bytes;
> > -		sge[sge_no].length = sge_bytes;
> > -		sge[sge_no].lkey = xprt->sc_phys_mr->lkey;
> > +		vec->sge[sge_no].iov_len = sge_bytes;
> >  
> >  		sge_no++;
> >  		page_no++;
> > @@ -117,23 +109,17 @@ static struct ib_sge *xdr_to_sge(struct svcxprt_rdma *xprt,
> >  
> >  	/* Tail SGE */
> >  	if (byte_count && xdr->tail[0].iov_len) {
> > -		sge[sge_no].addr =
> > -			ib_dma_map_single(xprt->sc_cm_id->device,
> > -					  xdr->tail[0].iov_base,
> > -					  xdr->tail[0].iov_len,
> > -					  DMA_TO_DEVICE);
> > +		vec->sge[sge_no].iov_base = xdr->tail[0].iov_base;
> >  		sge_bytes = min_t(u32, byte_count, xdr->tail[0].iov_len);
> >  		byte_count -= sge_bytes;
> > -		sge[sge_no].length = sge_bytes;
> > -		sge[sge_no].lkey = xprt->sc_phys_mr->lkey;
> > +		vec->sge[sge_no].iov_len = sge_bytes;
> >  		sge_no++;
> >  	}
> >  
> >  	BUG_ON(sge_no > sge_max);
> >  	BUG_ON(byte_count != 0);
> >  
> > -	*sge_count = sge_no;
> > -	return sge;
> > +	vec->count = sge_no;
> >  }
> >  
> >  
> > @@ -143,9 +129,8 @@ static struct ib_sge *xdr_to_sge(struct svcxprt_rdma *xprt,
> >  static int send_write(struct svcxprt_rdma *xprt, struct svc_rqst *rqstp,
> >  		      u32 rmr, u64 to,
> >  		      u32 xdr_off, int write_len,
> > -		      struct ib_sge *xdr_sge, int sge_count)
> > +		      struct svc_rdma_req_map *vec)
> >  {
> > -	struct svc_rdma_op_ctxt *tmp_sge_ctxt;
> >  	struct ib_send_wr write_wr;
> >  	struct ib_sge *sge;
> >  	int xdr_sge_no;
> > @@ -156,23 +141,22 @@ static int send_write(struct svcxprt_rdma *xprt, struct svc_rqst *rqstp,
> >  	struct svc_rdma_op_ctxt *ctxt;
> >  	int ret = 0;
> >  
> > -	BUG_ON(sge_count > RPCSVC_MAXPAGES);
> > +	BUG_ON(vec->count > RPCSVC_MAXPAGES);
> >  	dprintk("svcrdma: RDMA_WRITE rmr=%x, to=%llx, xdr_off=%d, "
> > -		"write_len=%d, xdr_sge=%p, sge_count=%d\n",
> > +		"write_len=%d, vec->sge=%p, vec->count=%lu\n",
> >  		rmr, (unsigned long long)to, xdr_off,
> > -		write_len, xdr_sge, sge_count);
> > +		write_len, vec->sge, vec->count);
> >  
> >  	ctxt = svc_rdma_get_context(xprt);
> > -	ctxt->count = 0;
> > -	tmp_sge_ctxt = svc_rdma_get_context(xprt);
> > -	sge = tmp_sge_ctxt->sge;
> > +	ctxt->direction = DMA_TO_DEVICE;
> > +	sge = ctxt->sge;
> >  
> >  	/* Find the SGE associated with xdr_off */
> > -	for (bc = xdr_off, xdr_sge_no = 1; bc && xdr_sge_no < sge_count;
> > +	for (bc = xdr_off, xdr_sge_no = 1; bc && xdr_sge_no < vec->count;
> >  	     xdr_sge_no++) {
> > -		if (xdr_sge[xdr_sge_no].length > bc)
> > +		if (vec->sge[xdr_sge_no].iov_len > bc)
> >  			break;
> > -		bc -= xdr_sge[xdr_sge_no].length;
> > +		bc -= vec->sge[xdr_sge_no].iov_len;
> >  	}
> >  
> >  	sge_off = bc;
> > @@ -180,21 +164,27 @@ static int send_write(struct svcxprt_rdma *xprt, struct svc_rqst *rqstp,
> >  	sge_no = 0;
> >  
> >  	/* Copy the remaining SGE */
> > -	while (bc != 0 && xdr_sge_no < sge_count) {
> > -		sge[sge_no].addr = xdr_sge[xdr_sge_no].addr + sge_off;
> > -		sge[sge_no].lkey = xdr_sge[xdr_sge_no].lkey;
> > +	while (bc != 0 && xdr_sge_no < vec->count) {
> > +		sge[sge_no].lkey = xprt->sc_phys_mr->lkey;
> >  		sge_bytes = min((size_t)bc,
> > -				(size_t)(xdr_sge[xdr_sge_no].length-sge_off));
> > +				(size_t)(vec->sge[xdr_sge_no].iov_len-sge_off));
> >  		sge[sge_no].length = sge_bytes;
> > -
> > +		sge[sge_no].addr =
> > +			ib_dma_map_single(xprt->sc_cm_id->device,
> > +					  (void *)
> > +					  vec->sge[xdr_sge_no].iov_base + sge_off,
> > +					  sge_bytes, DMA_TO_DEVICE);
> > +		if (dma_mapping_error(sge[sge_no].addr))
> > +			return -EINVAL;
> >     
>
> We leak a svc_rdma_op_ctxt on error here.
>
> --b.
>
>   
> >  		sge_off = 0;
> >  		sge_no++;
> > +		ctxt->count++;
> >  		xdr_sge_no++;
> >  		bc -= sge_bytes;
> >  	}
> >  
> >  	BUG_ON(bc != 0);
> > -	BUG_ON(xdr_sge_no > sge_count);
> > +	BUG_ON(xdr_sge_no > vec->count);
> >  
> >  	/* Prepare WRITE WR */
> >  	memset(&write_wr, 0, sizeof write_wr);
> > @@ -210,11 +200,10 @@ static int send_write(struct svcxprt_rdma *xprt, struct svc_rqst *rqstp,
> >  	/* Post It */
> >  	atomic_inc(&rdma_stat_write);
> >  	if (svc_rdma_send(xprt, &write_wr)) {
> > -		svc_rdma_put_context(ctxt, 1);
> > +		svc_rdma_put_context(ctxt, 0);
> >  		/* Fatal error, close transport */
> >  		ret = -EIO;
> >  	}
> > -	svc_rdma_put_context(tmp_sge_ctxt, 0);
> >  	return ret;
> >  }
> >  
> > @@ -222,8 +211,7 @@ static int send_write_chunks(struct svcxprt_rdma *xprt,
> >  			     struct rpcrdma_msg *rdma_argp,
> >  			     struct rpcrdma_msg *rdma_resp,
> >  			     struct svc_rqst *rqstp,
> > -			     struct ib_sge *sge,
> > -			     int sge_count)
> > +			     struct svc_rdma_req_map *vec)
> >  {
> >  	u32 xfer_len = rqstp->rq_res.page_len + rqstp->rq_res.tail[0].iov_len;
> >  	int write_len;
> > @@ -269,8 +257,7 @@ static int send_write_chunks(struct svcxprt_rdma *xprt,
> >  					 rs_offset + chunk_off,
> >  					 xdr_off,
> >  					 this_write,
> > -					 sge,
> > -					 sge_count);
> > +					 vec);
> >  			if (ret) {
> >  				dprintk("svcrdma: RDMA_WRITE failed, ret=%d\n",
> >  					ret);
> > @@ -292,8 +279,7 @@ static int send_reply_chunks(struct svcxprt_rdma *xprt,
> >  			     struct rpcrdma_msg *rdma_argp,
> >  			     struct rpcrdma_msg *rdma_resp,
> >  			     struct svc_rqst *rqstp,
> > -			     struct ib_sge *sge,
> > -			     int sge_count)
> > +			     struct svc_rdma_req_map *vec)
> >  {
> >  	u32 xfer_len = rqstp->rq_res.len;
> >  	int write_len;
> > @@ -341,8 +327,7 @@ static int send_reply_chunks(struct svcxprt_rdma *xprt,
> >  					 rs_offset + chunk_off,
> >  					 xdr_off,
> >  					 this_write,
> > -					 sge,
> > -					 sge_count);
> > +					 vec);
> >  			if (ret) {
> >  				dprintk("svcrdma: RDMA_WRITE failed, ret=%d\n",
> >  					ret);
> > @@ -380,7 +365,7 @@ static int send_reply(struct svcxprt_rdma *rdma,
> >  		      struct page *page,
> >  		      struct rpcrdma_msg *rdma_resp,
> >  		      struct svc_rdma_op_ctxt *ctxt,
> > -		      int sge_count,
> > +		      struct svc_rdma_req_map *vec,
> >  		      int byte_count)
> >  {
> >  	struct ib_send_wr send_wr;
> > @@ -413,10 +398,15 @@ static int send_reply(struct svcxprt_rdma *rdma,
> >  	ctxt->sge[0].lkey = rdma->sc_phys_mr->lkey;
> >  
> >  	/* Determine how many of our SGE are to be transmitted */
> > -	for (sge_no = 1; byte_count && sge_no < sge_count; sge_no++) {
> > -		sge_bytes = min((size_t)ctxt->sge[sge_no].length,
> > -				(size_t)byte_count);
> > +	for (sge_no = 1; byte_count && sge_no < vec->count; sge_no++) {
> > +		sge_bytes = min_t(size_t, vec->sge[sge_no].iov_len, byte_count);
> >  		byte_count -= sge_bytes;
> > +		ctxt->sge[sge_no].addr =
> > +			ib_dma_map_single(rdma->sc_cm_id->device,
> > +					  vec->sge[sge_no].iov_base,
> > +					  sge_bytes, DMA_TO_DEVICE);
> > +		ctxt->sge[sge_no].length = sge_bytes;
> > +		ctxt->sge[sge_no].lkey = rdma->sc_phys_mr->lkey;
> >  	}
> >  	BUG_ON(byte_count != 0);
> >  
> > @@ -428,8 +418,10 @@ static int send_reply(struct svcxprt_rdma *rdma,
> >  		ctxt->pages[page_no+1] = rqstp->rq_respages[page_no];
> >  		ctxt->count++;
> >  		rqstp->rq_respages[page_no] = NULL;
> > +		/* If there are more pages than SGE, terminate SGE list */
> > +		if (page_no+1 >= sge_no)
> > +			ctxt->sge[page_no+1].length = 0;
> >  	}
> > -
> >  	BUG_ON(sge_no > rdma->sc_max_sge);
> >  	memset(&send_wr, 0, sizeof send_wr);
> >  	ctxt->wr_op = IB_WR_SEND;
> > @@ -473,20 +465,20 @@ int svc_rdma_sendto(struct svc_rqst *rqstp)
> >  	enum rpcrdma_proc reply_type;
> >  	int ret;
> >  	int inline_bytes;
> > -	struct ib_sge *sge;
> > -	int sge_count = 0;
> >  	struct page *res_page;
> >  	struct svc_rdma_op_ctxt *ctxt;
> > +	struct svc_rdma_req_map *vec;
> >  
> >  	dprintk("svcrdma: sending response for rqstp=%p\n", rqstp);
> >  
> >  	/* Get the RDMA request header. */
> >  	rdma_argp = xdr_start(&rqstp->rq_arg);
> >  
> > -	/* Build an SGE for the XDR */
> > +	/* Build an req vec for the XDR */
> >  	ctxt = svc_rdma_get_context(rdma);
> >  	ctxt->direction = DMA_TO_DEVICE;
> > -	sge = xdr_to_sge(rdma, &rqstp->rq_res, ctxt->sge, &sge_count);
> > +	vec = svc_rdma_get_req_map();
> > +	xdr_to_sge(rdma, &rqstp->rq_res, vec);
> >  
> >  	inline_bytes = rqstp->rq_res.len;
> >  
> > @@ -503,7 +495,7 @@ int svc_rdma_sendto(struct svc_rqst *rqstp)
> >  
> >  	/* Send any write-chunk data and build resp write-list */
> >  	ret = send_write_chunks(rdma, rdma_argp, rdma_resp,
> > -				rqstp, sge, sge_count);
> > +				rqstp, vec);
> >  	if (ret < 0) {
> >  		printk(KERN_ERR "svcrdma: failed to send write chunks, rc=%d\n",
> >  		       ret);
> > @@ -513,7 +505,7 @@ int svc_rdma_sendto(struct svc_rqst *rqstp)
> >  
> >  	/* Send any reply-list data and update resp reply-list */
> >  	ret = send_reply_chunks(rdma, rdma_argp, rdma_resp,
> > -				rqstp, sge, sge_count);
> > +				rqstp, vec);
> >  	if (ret < 0) {
> >  		printk(KERN_ERR "svcrdma: failed to send reply chunks, rc=%d\n",
> >  		       ret);
> > @@ -521,11 +513,13 @@ int svc_rdma_sendto(struct svc_rqst *rqstp)
> >  	}
> >  	inline_bytes -= ret;
> >  
> > -	ret = send_reply(rdma, rqstp, res_page, rdma_resp, ctxt, sge_count,
> > +	ret = send_reply(rdma, rqstp, res_page, rdma_resp, ctxt, vec,
> >  			 inline_bytes);
> > +	svc_rdma_put_req_map(vec);
> >  	dprintk("svcrdma: send_reply returns %d\n", ret);
> >  	return ret;
> >   error:
> > +	svc_rdma_put_req_map(vec);
> >  	svc_rdma_put_context(ctxt, 0);
> >  	put_page(res_page);
> >  	return ret;
> > diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
> > index ae90758..fc86338 100644
> > --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
> > +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
> > @@ -387,10 +387,13 @@ static void sq_cq_reap(struct svcxprt_rdma *xprt)
> >  
> >  		switch (ctxt->wr_op) {
> >  		case IB_WR_SEND:
> > -		case IB_WR_RDMA_WRITE:
> >  			svc_rdma_put_context(ctxt, 1);
> >  			break;
> >  
> > +		case IB_WR_RDMA_WRITE:
> > +			svc_rdma_put_context(ctxt, 0);
> > +			break;
> > +
> >  		case IB_WR_RDMA_READ:
> >  			if (test_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags)) {
> >  				struct svc_rdma_op_ctxt *read_hdr = ctxt->read_hdr;
> >     
> --
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