Re: [PATCH RFC 6/6] svcrdma: Pull Read chunks in ->xpo_argument_payload

[Chuck Lever III <chuck.lever@oracle.com>]

> On Aug 31, 2021, at 3:05 PM, Chuck Lever <chuck.lever@oracle.com> wrote:
> 
> This enables the XDR decoder to figure out how the payload sink
> buffer needs to be aligned before setting up the RDMA Reads.
> Then re-alignment of large RDMA Read payloads can be avoided.

Should say "can be avoided" but isn't yet. All of these patches
are pre-requisites to that behavior.


> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
> include/linux/sunrpc/svc_rdma.h         |    6 +
> include/trace/events/rpcrdma.h          |   26 ++++++
> net/sunrpc/xprtrdma/svc_rdma_recvfrom.c |   17 +++-
> net/sunrpc/xprtrdma/svc_rdma_rw.c       |  139 ++++++++++++++++++++++++++++---
> 4 files changed, 169 insertions(+), 19 deletions(-)
> 
> diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
> index f660244cc8ba..8d80a759a909 100644
> --- a/include/linux/sunrpc/svc_rdma.h
> +++ b/include/linux/sunrpc/svc_rdma.h
> @@ -192,6 +192,12 @@ extern int svc_rdma_send_reply_chunk(struct svcxprt_rdma *rdma,
> extern int svc_rdma_process_read_list(struct svcxprt_rdma *rdma,
> 				      struct svc_rqst *rqstp,
> 				      struct svc_rdma_recv_ctxt *head);
> +extern void svc_rdma_prepare_read_chunk(struct svc_rqst *rqstp,
> +					struct svc_rdma_recv_ctxt *head);
> +extern int svc_rdma_pull_read_chunk(struct svcxprt_rdma *rdma,
> +				    struct svc_rqst *rqstp,
> +				    struct svc_rdma_recv_ctxt *ctxt,
> +				    unsigned int offset, unsigned int length);
> 
> /* svc_rdma_sendto.c */
> extern void svc_rdma_send_ctxts_destroy(struct svcxprt_rdma *rdma);
> diff --git a/include/trace/events/rpcrdma.h b/include/trace/events/rpcrdma.h
> index 5954ce036173..30440cca321a 100644
> --- a/include/trace/events/rpcrdma.h
> +++ b/include/trace/events/rpcrdma.h
> @@ -2136,6 +2136,32 @@ TRACE_EVENT(svcrdma_sq_post_err,
> 	)
> );
> 
> +TRACE_EVENT(svcrdma_arg_payload,
> +	TP_PROTO(
> +		const struct svc_rqst *rqstp,
> +		unsigned int offset,
> +		unsigned int length
> +	),
> +
> +	TP_ARGS(rqstp, offset, length),
> +
> +	TP_STRUCT__entry(
> +		__field(u32, xid)
> +		__field(u32, offset)
> +		__field(u32, length)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->xid = __be32_to_cpu(rqstp->rq_xid);
> +		__entry->offset = offset_in_page(offset);
> +		__entry->length = length;
> +	),
> +
> +	TP_printk("xid=0x%08x offset=%u length=%u",
> +		__entry->xid, __entry->offset, __entry->length
> +	)
> +);
> +
> #endif /* _TRACE_RPCRDMA_H */
> 
> #include <trace/define_trace.h>
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> index 08a620b370ae..cd9c0fb1a470 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> @@ -838,12 +838,13 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
> 
> 	svc_rdma_get_inv_rkey(rdma_xprt, ctxt);
> 
> -	if (!pcl_is_empty(&ctxt->rc_read_pcl) ||
> -	    !pcl_is_empty(&ctxt->rc_call_pcl)) {
> +	if (!pcl_is_empty(&ctxt->rc_call_pcl) ||
> +	    ctxt->rc_read_pcl.cl_count > 1) {
> 		ret = svc_rdma_process_read_list(rdma_xprt, rqstp, ctxt);
> 		if (ret < 0)
> 			goto out_readfail;
> -	}
> +	} else if (ctxt->rc_read_pcl.cl_count == 1)
> +		svc_rdma_prepare_read_chunk(rqstp, ctxt);
> 
> 	rqstp->rq_xprt_ctxt = ctxt;
> 	rqstp->rq_prot = IPPROTO_MAX;
> @@ -887,5 +888,13 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
> int svc_rdma_argument_payload(struct svc_rqst *rqstp, unsigned int offset,
> 			      unsigned int length)
> {
> -	return 0;
> +	struct svc_rdma_recv_ctxt *ctxt = rqstp->rq_xprt_ctxt;
> +	struct svc_xprt *xprt = rqstp->rq_xprt;
> +	struct svcxprt_rdma *rdma =
> +		container_of(xprt, struct svcxprt_rdma, sc_xprt);
> +
> +	if (!pcl_is_empty(&ctxt->rc_call_pcl) ||
> +	    ctxt->rc_read_pcl.cl_count != 1)
> +		return 0;
> +	return svc_rdma_pull_read_chunk(rdma, rqstp, ctxt, offset, length);
> }
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_rw.c b/net/sunrpc/xprtrdma/svc_rdma_rw.c
> index 29b7d477891c..5f03dfd2fa03 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_rw.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_rw.c
> @@ -707,19 +707,24 @@ static int svc_rdma_build_read_segment(struct svc_rdma_read_info *info,
> 
> 	len = segment->rs_length;
> 	sge_no = PAGE_ALIGN(info->ri_pageoff + len) >> PAGE_SHIFT;
> +
> +	trace_printk("pageoff=%u len=%u sges=%u\n",
> +		info->ri_pageoff, len, sge_no);
> +
> 	ctxt = svc_rdma_get_rw_ctxt(cc->cc_rdma, sge_no);
> 	if (!ctxt)
> 		return -ENOMEM;
> 	ctxt->rw_nents = sge_no;
> +	head->rc_page_count += sge_no;
> 
> 	sg = ctxt->rw_sg_table.sgl;
> 	for (sge_no = 0; sge_no < ctxt->rw_nents; sge_no++) {
> 		seg_len = min_t(unsigned int, len,
> 				PAGE_SIZE - info->ri_pageoff);
> 
> -		if (!info->ri_pageoff)
> -			head->rc_page_count++;
> -
> +		trace_printk("  page=%p seg_len=%u offset=%u\n",
> +			rqstp->rq_pages[info->ri_pageno], seg_len,
> +			info->ri_pageoff);
> 		sg_set_page(sg, rqstp->rq_pages[info->ri_pageno],
> 			    seg_len, info->ri_pageoff);
> 		sg = sg_next(sg);
> @@ -804,15 +809,14 @@ static int svc_rdma_copy_inline_range(struct svc_rdma_read_info *info,
> 	unsigned int page_no, numpages;
> 
> 	numpages = PAGE_ALIGN(info->ri_pageoff + remaining) >> PAGE_SHIFT;
> +	head->rc_page_count += numpages;
> +
> 	for (page_no = 0; page_no < numpages; page_no++) {
> 		unsigned int page_len;
> 
> 		page_len = min_t(unsigned int, remaining,
> 				 PAGE_SIZE - info->ri_pageoff);
> 
> -		if (!info->ri_pageoff)
> -			head->rc_page_count++;
> -
> 		dst = page_address(rqstp->rq_pages[info->ri_pageno]);
> 		memcpy(dst + info->ri_pageno, src + offset, page_len);
> 
> @@ -1092,15 +1096,8 @@ static noinline int svc_rdma_read_special(struct svc_rdma_read_info *info)
>  * @rqstp: set of pages to use as Read sink buffers
>  * @head: pages under I/O collect here
>  *
> - * The RPC/RDMA protocol assumes that the upper layer's XDR decoders
> - * pull each Read chunk as they decode an incoming RPC message.
> - *
> - * On Linux, however, the server needs to have a fully-constructed RPC
> - * message in rqstp->rq_arg when there is a positive return code from
> - * ->xpo_recvfrom. So the Read list is safety-checked immediately when
> - * it is received, then here the whole Read list is pulled all at once.
> - * The ingress RPC message is fully reconstructed once all associated
> - * RDMA Reads have completed.
> + * Handle complex Read chunk cases fully before svc_rdma_recvfrom()
> + * returns.
>  *
>  * Return values:
>  *   %1: all needed RDMA Reads were posted successfully,
> @@ -1159,3 +1156,115 @@ int svc_rdma_process_read_list(struct svcxprt_rdma *rdma,
> 	svc_rdma_read_info_free(info);
> 	return ret;
> }
> +
> +/**
> + * svc_rdma_prepare_read_chunk - Prepare rq_arg for Read chunk
> + * @rqstp: set of pages to use as Read sink buffers
> + * @head: pages under I/O collect here
> + *
> + * The Read chunk will be pulled when the upper layer's XDR
> + * decoder calls svc_decode_argument_payload(). In the meantime,
> + * fake up rq_arg.page_len and .len to reflect the size of the
> + * yet-to-be-pulled payload.
> + */
> +void svc_rdma_prepare_read_chunk(struct svc_rqst *rqstp,
> +				 struct svc_rdma_recv_ctxt *head)
> +{
> +	struct svc_rdma_chunk *chunk = pcl_first_chunk(&head->rc_read_pcl);
> +	unsigned int length = xdr_align_size(chunk->ch_length);
> +	struct xdr_buf *buf = &rqstp->rq_arg;
> +
> +	buf->tail[0].iov_base = buf->head[0].iov_base + chunk->ch_position;
> +	buf->tail[0].iov_len = buf->head[0].iov_len - chunk->ch_position;
> +	buf->head[0].iov_len = chunk->ch_position;
> +
> +	buf->page_len = length;
> +	buf->len += length;
> +	buf->buflen += length;
> +
> +	/*
> +	 * rq_respages starts after the last arg page. Note that we
> +	 * don't know the offset yet, so add an extra page as slack.
> +	 */
> +	length += PAGE_SIZE * 2 - 1;
> +	rqstp->rq_respages = &rqstp->rq_pages[length >> PAGE_SHIFT];
> +	rqstp->rq_next_page = rqstp->rq_respages + 1;
> +}
> +
> +/**
> + * svc_rdma_pull_read_chunk - Pull one Read chunk from the client
> + * @rdma: controlling RDMA transport
> + * @rqstp: set of pages to use as Read sink buffers
> + * @head: pages under I/O collect here
> + * @offset: offset of payload in file's page cache
> + * @length: size of payload, in bytes
> + *
> + * Once the upper layer's XDR decoder has decoded the length of
> + * the payload and it's offset, we can be clever about setting up
> + * the RDMA Read sink buffer so that the VFS does not have to
> + * re-align the payload once it is received.
> + *
> + * Caveat: To keep things simple, this is an optimization that is
> + *	   used only when there is a single Read chunk in the Read
> + *	   list.
> + *
> + * Return values:
> + *   %0: all needed RDMA Reads were posted successfully,
> + *   %-EINVAL: client provided the wrong chunk size,
> + *   %-ENOMEM: rdma_rw context pool was exhausted,
> + *   %-ENOTCONN: posting failed (connection is lost),
> + *   %-EIO: rdma_rw initialization failed (DMA mapping, etc).
> + */
> +int svc_rdma_pull_read_chunk(struct svcxprt_rdma *rdma, struct svc_rqst *rqstp,
> +			     struct svc_rdma_recv_ctxt *head,
> +			     unsigned int offset, unsigned int length)
> +{
> +	struct svc_rdma_read_info *info;
> +	struct svc_rdma_chunk_ctxt *cc;
> +	struct svc_rdma_chunk *chunk;
> +	int ret;
> +
> +	trace_svcrdma_arg_payload(rqstp, offset, length);
> +
> +	/* Sanity: the Requester must have provided enough
> +	 * bytes to fill the XDR opaque.
> +	 */
> +	chunk = pcl_first_chunk(&head->rc_read_pcl);
> +	if (length > chunk->ch_length)
> +		return -EINVAL;
> +
> +	info = svc_rdma_read_info_alloc(rdma);
> +	if (!info)
> +		return -ENOMEM;
> +	cc = &info->ri_cc;
> +	info->ri_rqst = rqstp;
> +	info->ri_readctxt = head;
> +	info->ri_pageno = 0;
> +	info->ri_pageoff = offset_in_page(offset);
> +	info->ri_totalbytes = 0;
> +
> +	ret = svc_rdma_build_read_chunk(info, chunk);
> +	if (ret < 0)
> +		goto out_err;
> +	rqstp->rq_arg.pages = &info->ri_rqst->rq_pages[0];
> +	rqstp->rq_arg.page_base = offset_in_page(offset);
> +	rqstp->rq_arg.buflen += offset_in_page(offset);
> +
> +	trace_svcrdma_post_read_chunk(&cc->cc_cid, cc->cc_sqecount);
> +	init_completion(&cc->cc_done);
> +	ret = svc_rdma_post_chunk_ctxt(cc);
> +	if (ret < 0)
> +		goto out_err;
> +
> +	ret = 0;
> +	wait_for_completion(&cc->cc_done);
> +	if (cc->cc_status != IB_WC_SUCCESS)
> +		ret = -EIO;
> +
> +	/* Ensure svc_rdma_recv_ctxt_put() does not try to release pages */
> +	head->rc_page_count = 0;
> +
> +out_err:
> +	svc_rdma_read_info_free(info);
> +	return ret;
> +}
> 
> 

--
Chuck Lever