svcrdma: Introduce local rdma_rw API helpers

The plan is to replace the local bespoke code that constructs and
posts RDMA Read and Write Work Requests with calls to the rdma_rw
API. This shares code with other RDMA-enabled ULPs that manages the
gory details of buffer registration and posting Work Requests.

Some design notes:

 o The structure of RPC-over-RDMA transport headers is flexible,
   allowing multiple segments per Reply with arbitrary alignment,
   each with a unique R_key. Write and Send WRs continue to be
   built and posted in separate code paths. However, one whole
   chunk (with one or more RDMA segments apiece) gets exactly
   one ib_post_send and one work completion.

 o svc_xprt reference counting is modified, since a chain of
   rdma_rw_ctx structs generates one completion, no matter how
   many Write WRs are posted.

 o The current code builds the transport header as it is construct-
   ing Write WRs. I've replaced that with marshaling of transport
   header data items in a separate step. This is because the exact
   structure of client-provided segments may not align with the
   components of the server's reply xdr_buf, or the pages in the
   page list. Thus parts of each client-provided segment may be
   written at different points in the send path.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 512 insertions, 0 deletions

diff --git a/net/sunrpc/xprtrdma/svc_rdma_rw.c b/net/sunrpc/xprtrdma/svc_rdma_rw.c
new file mode 100644
index 000000000000..0cf620277693
--- /dev/null
+++ b/net/sunrpc/xprtrdma/svc_rdma_rw.c
@@ -0,0 +1,512 @@
+/*
+ * Copyright (c) 2016 Oracle.  All rights reserved.
+ *
+ * Use the core R/W API to move RPC-over-RDMA Read and Write chunks.
+ */
+
+#include <linux/sunrpc/rpc_rdma.h>
+#include <linux/sunrpc/svc_rdma.h>
+#include <linux/sunrpc/debug.h>
+
+#include <rdma/rw.h>
+
+#define RPCDBG_FACILITY	RPCDBG_SVCXPRT
+
+/* Each R/W context contains state for one chain of RDMA Read or
+ * Write Work Requests.
+ *
+ * Each WR chain handles a single contiguous server-side buffer,
+ * because scatterlist entries after the first have to start on
+ * page alignment. xdr_buf iovecs cannot guarantee alignment.
+ *
+ * Each WR chain handles only one R_key. Each RPC-over-RDMA segment
+ * from a client may contain a unique R_key, so each WR chain moves
+ * up to one segment at a time.
+ *
+ * The scatterlist makes this data structure over 4KB in size. To
+ * make it less likely to fail, and to handle the allocation for
+ * smaller I/O requests without disabling bottom-halves, these
+ * contexts are created on demand, but cached and reused until the
+ * controlling svcxprt_rdma is destroyed.
+ */
+struct svc_rdma_rw_ctxt {
+	struct list_head	rw_list;
+	struct rdma_rw_ctx	rw_ctx;
+	int			rw_nents;
+	struct sg_table		rw_sg_table;
+	struct scatterlist	rw_first_sgl[0];
+};
+
+static inline struct svc_rdma_rw_ctxt *
+svc_rdma_next_ctxt(struct list_head *list)
+{
+	return list_first_entry_or_null(list, struct svc_rdma_rw_ctxt,
+					rw_list);
+}
+
+static struct svc_rdma_rw_ctxt *
+svc_rdma_get_rw_ctxt(struct svcxprt_rdma *rdma, unsigned int sges)
+{
+	struct svc_rdma_rw_ctxt *ctxt;
+
+	spin_lock(&rdma->sc_rw_ctxt_lock);
+
+	ctxt = svc_rdma_next_ctxt(&rdma->sc_rw_ctxts);
+	if (ctxt) {
+		list_del(&ctxt->rw_list);
+		spin_unlock(&rdma->sc_rw_ctxt_lock);
+	} else {
+		spin_unlock(&rdma->sc_rw_ctxt_lock);
+		ctxt = kmalloc(sizeof(*ctxt) +
+			       SG_CHUNK_SIZE * sizeof(struct scatterlist),
+			       GFP_KERNEL);
+		if (!ctxt)
+			goto out;
+		INIT_LIST_HEAD(&ctxt->rw_list);
+	}
+
+	ctxt->rw_sg_table.sgl = ctxt->rw_first_sgl;
+	if (sg_alloc_table_chained(&ctxt->rw_sg_table, sges,
+				   ctxt->rw_sg_table.sgl)) {
+		kfree(ctxt);
+		ctxt = NULL;
+	}
+out:
+	return ctxt;
+}
+
+static void svc_rdma_put_rw_ctxt(struct svcxprt_rdma *rdma,
+				 struct svc_rdma_rw_ctxt *ctxt)
+{
+	sg_free_table_chained(&ctxt->rw_sg_table, true);
+
+	spin_lock(&rdma->sc_rw_ctxt_lock);
+	list_add(&ctxt->rw_list, &rdma->sc_rw_ctxts);
+	spin_unlock(&rdma->sc_rw_ctxt_lock);
+}
+
+/**
+ * svc_rdma_destroy_rw_ctxts - Free accumulated R/W contexts
+ * @rdma: transport about to be destroyed
+ *
+ */
+void svc_rdma_destroy_rw_ctxts(struct svcxprt_rdma *rdma)
+{
+	struct svc_rdma_rw_ctxt *ctxt;
+
+	while ((ctxt = svc_rdma_next_ctxt(&rdma->sc_rw_ctxts)) != NULL) {
+		list_del(&ctxt->rw_list);
+		kfree(ctxt);
+	}
+}
+
+/* A chunk context tracks all I/O for moving one Read or Write
+ * chunk. This is a a set of rdma_rw's that handle data movement
+ * for all segments of one chunk.
+ *
+ * These are small, acquired with a single allocator call, and
+ * no more than one is needed per chunk. They are allocated on
+ * demand, and not cached.
+ */
+struct svc_rdma_chunk_ctxt {
+	struct ib_cqe		cc_cqe;
+	struct svcxprt_rdma	*cc_rdma;
+	struct list_head	cc_rwctxts;
+	int			cc_sqecount;
+	enum dma_data_direction cc_dir;
+};
+
+static void svc_rdma_cc_init(struct svcxprt_rdma *rdma,
+			     struct svc_rdma_chunk_ctxt *cc,
+			     enum dma_data_direction dir)
+{
+	cc->cc_rdma = rdma;
+	svc_xprt_get(&rdma->sc_xprt);
+
+	INIT_LIST_HEAD(&cc->cc_rwctxts);
+	cc->cc_sqecount = 0;
+	cc->cc_dir = dir;
+}
+
+static void svc_rdma_cc_release(struct svc_rdma_chunk_ctxt *cc)
+{
+	struct svcxprt_rdma *rdma = cc->cc_rdma;
+	struct svc_rdma_rw_ctxt *ctxt;
+
+	while ((ctxt = svc_rdma_next_ctxt(&cc->cc_rwctxts)) != NULL) {
+		list_del(&ctxt->rw_list);
+
+		rdma_rw_ctx_destroy(&ctxt->rw_ctx, rdma->sc_qp,
+				    rdma->sc_port_num, ctxt->rw_sg_table.sgl,
+				    ctxt->rw_nents, cc->cc_dir);
+		svc_rdma_put_rw_ctxt(rdma, ctxt);
+	}
+	svc_xprt_put(&rdma->sc_xprt);
+}
+
+/* State for sending a Write or Reply chunk.
+ *  - Tracks progress of writing one chunk over all its segments
+ *  - Stores arguments for the SGL constructor functions
+ */
+struct svc_rdma_write_info {
+	/* write state of this chunk */
+	unsigned int		wi_seg_off;
+	unsigned int		wi_seg_no;
+	unsigned int		wi_nsegs;
+	__be32			*wi_segs;
+
+	/* SGL constructor arguments */
+	struct xdr_buf		*wi_xdr;
+	unsigned char		*wi_base;
+	unsigned int		wi_next_off;
+
+	struct svc_rdma_chunk_ctxt	wi_cc;
+};
+
+static struct svc_rdma_write_info *
+svc_rdma_write_info_alloc(struct svcxprt_rdma *rdma, __be32 *chunk)
+{
+	struct svc_rdma_write_info *info;
+
+	info = kmalloc(sizeof(*info), GFP_KERNEL);
+	if (!info)
+		return info;
+
+	info->wi_seg_off = 0;
+	info->wi_seg_no = 0;
+	info->wi_nsegs = be32_to_cpup(++chunk);
+	info->wi_segs = ++chunk;
+	svc_rdma_cc_init(rdma, &info->wi_cc, DMA_TO_DEVICE);
+	return info;
+}
+
+static void svc_rdma_write_info_free(struct svc_rdma_write_info *info)
+{
+	svc_rdma_cc_release(&info->wi_cc);
+	kfree(info);
+}
+
+/**
+ * svc_rdma_write_done - Write chunk completion
+ * @cq: controlling Completion Queue
+ * @wc: Work Completion
+ *
+ * Pages under I/O are freed by a subsequent Send completion.
+ */
+static void svc_rdma_write_done(struct ib_cq *cq, struct ib_wc *wc)
+{
+	struct ib_cqe *cqe = wc->wr_cqe;
+	struct svc_rdma_chunk_ctxt *cc =
+			container_of(cqe, struct svc_rdma_chunk_ctxt, cc_cqe);
+	struct svcxprt_rdma *rdma = cc->cc_rdma;
+	struct svc_rdma_write_info *info =
+			container_of(cc, struct svc_rdma_write_info, wi_cc);
+
+	atomic_add(cc->cc_sqecount, &rdma->sc_sq_avail);
+	wake_up(&rdma->sc_send_wait);
+
+	if (unlikely(wc->status != IB_WC_SUCCESS)) {
+		set_bit(XPT_CLOSE, &rdma->sc_xprt.xpt_flags);
+		if (wc->status != IB_WC_WR_FLUSH_ERR)
+			pr_err("svcrdma: write ctx: %s (%u/0x%x)\n",
+			       ib_wc_status_msg(wc->status),
+			       wc->status, wc->vendor_err);
+	}
+
+	svc_rdma_write_info_free(info);
+}
+
+/* This function sleeps when the transport's Send Queue is congested.
+ *
+ * Assumptions:
+ * - If ib_post_send() succeeds, only one completion is expected,
+ *   even if one or more WRs are flushed. This is true when posting
+ *   an rdma_rw_ctx or when posting a single signaled WR.
+ */
+static int svc_rdma_post_chunk_ctxt(struct svc_rdma_chunk_ctxt *cc)
+{
+	struct svcxprt_rdma *rdma = cc->cc_rdma;
+	struct svc_xprt *xprt = &rdma->sc_xprt;
+	struct ib_send_wr *first_wr, *bad_wr;
+	struct list_head *tmp;
+	struct ib_cqe *cqe;
+	int ret;
+
+	first_wr = NULL;
+	cqe = &cc->cc_cqe;
+	list_for_each(tmp, &cc->cc_rwctxts) {
+		struct svc_rdma_rw_ctxt *ctxt;
+
+		ctxt = list_entry(tmp, struct svc_rdma_rw_ctxt, rw_list);
+		first_wr = rdma_rw_ctx_wrs(&ctxt->rw_ctx, rdma->sc_qp,
+					   rdma->sc_port_num, cqe, first_wr);
+		cqe = NULL;
+	}
+
+	do {
+		if (atomic_sub_return(cc->cc_sqecount,
+				      &rdma->sc_sq_avail) > 0) {
+			ret = ib_post_send(rdma->sc_qp, first_wr, &bad_wr);
+			if (ret)
+				break;
+			return 0;
+		}
+
+		atomic_inc(&rdma_stat_sq_starve);
+		atomic_add(cc->cc_sqecount, &rdma->sc_sq_avail);
+		wait_event(rdma->sc_send_wait,
+			   atomic_read(&rdma->sc_sq_avail) > cc->cc_sqecount);
+	} while (1);
+
+	pr_err("svcrdma: ib_post_send failed (%d)\n", ret);
+	set_bit(XPT_CLOSE, &xprt->xpt_flags);
+
+	/* If even one was posted, there will be a completion. */
+	if (bad_wr != first_wr)
+		return 0;
+
+	atomic_add(cc->cc_sqecount, &rdma->sc_sq_avail);
+	wake_up(&rdma->sc_send_wait);
+	return -ENOTCONN;
+}
+
+/* Build and DMA-map an SGL that covers one kvec in an xdr_buf
+ */
+static void svc_rdma_vec_to_sg(struct svc_rdma_write_info *info,
+			       unsigned int len,
+			       struct svc_rdma_rw_ctxt *ctxt)
+{
+	struct scatterlist *sg = ctxt->rw_sg_table.sgl;
+
+	sg_set_buf(&sg[0], info->wi_base, len);
+	info->wi_base += len;
+
+	ctxt->rw_nents = 1;
+}
+
+/* Build and DMA-map an SGL that covers part of an xdr_buf's pagelist.
+ */
+static void svc_rdma_pagelist_to_sg(struct svc_rdma_write_info *info,
+				    unsigned int remaining,
+				    struct svc_rdma_rw_ctxt *ctxt)
+{
+	unsigned int sge_no, sge_bytes, page_off, page_no;
+	struct xdr_buf *xdr = info->wi_xdr;
+	struct scatterlist *sg;
+	struct page **page;
+
+	page_off = (info->wi_next_off + xdr->page_base) & ~PAGE_MASK;
+	page_no = (info->wi_next_off + xdr->page_base) >> PAGE_SHIFT;
+	page = xdr->pages + page_no;
+	info->wi_next_off += remaining;
+	sg = ctxt->rw_sg_table.sgl;
+	sge_no = 0;
+	do {
+		sge_bytes = min_t(unsigned int, remaining,
+				  PAGE_SIZE - page_off);
+		sg_set_page(sg, *page, sge_bytes, page_off);
+
+		remaining -= sge_bytes;
+		sg = sg_next(sg);
+		page_off = 0;
+		sge_no++;
+		page++;
+	} while (remaining);
+
+	ctxt->rw_nents = sge_no;
+}
+
+/* Construct RDMA Write WRs to send a portion of an xdr_buf containing
+ * an RPC Reply.
+ */
+static int
+svc_rdma_build_writes(struct svc_rdma_write_info *info,
+		      void (*constructor)(struct svc_rdma_write_info *info,
+					  unsigned int len,
+					  struct svc_rdma_rw_ctxt *ctxt),
+		      unsigned int remaining)
+{
+	struct svc_rdma_chunk_ctxt *cc = &info->wi_cc;
+	struct svcxprt_rdma *rdma = cc->cc_rdma;
+	struct svc_rdma_rw_ctxt *ctxt;
+	__be32 *seg;
+	int ret;
+
+	cc->cc_cqe.done = svc_rdma_write_done;
+	seg = info->wi_segs + info->wi_seg_no * rpcrdma_segment_maxsz;
+	do {
+		unsigned int write_len;
+		u32 seg_length, seg_handle;
+		u64 seg_offset;
+
+		if (info->wi_seg_no >= info->wi_nsegs)
+			goto out_overflow;
+
+		seg_handle = be32_to_cpup(seg);
+		seg_length = be32_to_cpup(seg + 1);
+		xdr_decode_hyper(seg + 2, &seg_offset);
+		seg_offset += info->wi_seg_off;
+
+		write_len = min(remaining, seg_length - info->wi_seg_off);
+		ctxt = svc_rdma_get_rw_ctxt(rdma,
+					    (write_len >> PAGE_SHIFT) + 2);
+		if (!ctxt)
+			goto out_noctx;
+
+		constructor(info, write_len, ctxt);
+		ret = rdma_rw_ctx_init(&ctxt->rw_ctx, rdma->sc_qp,
+				       rdma->sc_port_num, ctxt->rw_sg_table.sgl,
+				       ctxt->rw_nents, 0, seg_offset,
+				       seg_handle, DMA_TO_DEVICE);
+		if (ret < 0)
+			goto out_initerr;
+
+		list_add(&ctxt->rw_list, &cc->cc_rwctxts);
+		cc->cc_sqecount += ret;
+		if (write_len == seg_length - info->wi_seg_off) {
+			seg += 4;
+			info->wi_seg_no++;
+			info->wi_seg_off = 0;
+		} else {
+			info->wi_seg_off += write_len;
+		}
+		remaining -= write_len;
+	} while (remaining);
+
+	return 0;
+
+out_overflow:
+	dprintk("svcrdma: inadequate space in Write chunk (%u)\n",
+		info->wi_nsegs);
+	return -E2BIG;
+
+out_noctx:
+	dprintk("svcrdma: no R/W ctxs available\n");
+	return -ENOMEM;
+
+out_initerr:
+	svc_rdma_put_rw_ctxt(rdma, ctxt);
+	pr_err("svcrdma: failed to map pagelist (%d)\n", ret);
+	return -EIO;
+}
+
+/* Send one of an xdr_buf's kvecs by itself. To send a Reply
+ * chunk, the whole RPC Reply is written back to the client.
+ * This function writes either the head or tail of the xdr_buf
+ * containing the Reply.
+ */
+static int svc_rdma_send_xdr_kvec(struct svc_rdma_write_info *info,
+				  struct kvec *vec)
+{
+	info->wi_base = vec->iov_base;
+	return svc_rdma_build_writes(info, svc_rdma_vec_to_sg,
+				     vec->iov_len);
+}
+
+/* Send an xdr_buf's page list by itself. A Write chunk is
+ * just the page list. a Reply chunk is the head, page list,
+ * and tail. This function is shared between the two types
+ * of chunk.
+ */
+static int svc_rdma_send_xdr_pagelist(struct svc_rdma_write_info *info,
+				      struct xdr_buf *xdr)
+{
+	info->wi_xdr = xdr;
+	info->wi_next_off = 0;
+	return svc_rdma_build_writes(info, svc_rdma_pagelist_to_sg,
+				     xdr->page_len);
+}
+
+/**
+ * svc_rdma_send_write_chunk - Write all segments in a Write chunk
+ * @rdma: controlling RDMA transport
+ * @wr_ch: Write chunk provided by client
+ * @xdr: xdr_buf containing the data payload
+ *
+ * Returns a non-negative number of bytes the chunk consumed, or
+ *	%-E2BIG if the payload was larger than the Write chunk,
+ *	%-ENOMEM if rdma_rw context pool was exhausted,
+ *	%-ENOTCONN if posting failed (connection is lost),
+ *	%-EIO if rdma_rw initialization failed (DMA mapping, etc).
+ */
+int svc_rdma_send_write_chunk(struct svcxprt_rdma *rdma, __be32 *wr_ch,
+			      struct xdr_buf *xdr)
+{
+	struct svc_rdma_write_info *info;
+	int ret;
+
+	if (!xdr->page_len)
+		return 0;
+
+	info = svc_rdma_write_info_alloc(rdma, wr_ch);
+	if (!info)
+		return -ENOMEM;
+
+	ret = svc_rdma_send_xdr_pagelist(info, xdr);
+	if (ret < 0)
+		goto out_err;
+
+	ret = svc_rdma_post_chunk_ctxt(&info->wi_cc);
+	if (ret < 0)
+		goto out_err;
+	return xdr->page_len;
+
+out_err:
+	svc_rdma_write_info_free(info);
+	return ret;
+}
+
+/**
+ * svc_rdma_send_reply_chunk - Write all segments in the Reply chunk
+ * @rdma: controlling RDMA transport
+ * @rp_ch: Reply chunk provided by client
+ * @writelist: true if client provided a Write list
+ * @xdr: xdr_buf containing an RPC Reply
+ *
+ * Returns a non-negative number of bytes the chunk consumed, or
+ *	%-E2BIG if the payload was larger than the Reply chunk,
+ *	%-ENOMEM if rdma_rw context pool was exhausted,
+ *	%-ENOTCONN if posting failed (connection is lost),
+ *	%-EIO if rdma_rw initialization failed (DMA mapping, etc).
+ */
+int svc_rdma_send_reply_chunk(struct svcxprt_rdma *rdma, __be32 *rp_ch,
+			      bool writelist, struct xdr_buf *xdr)
+{
+	struct svc_rdma_write_info *info;
+	int consumed, ret;
+
+	info = svc_rdma_write_info_alloc(rdma, rp_ch);
+	if (!info)
+		return -ENOMEM;
+
+	ret = svc_rdma_send_xdr_kvec(info, &xdr->head[0]);
+	if (ret < 0)
+		goto out_err;
+	consumed = xdr->head[0].iov_len;
+
+	/* Send the page list in the Reply chunk only if the
+	 * client did not provide Write chunks.
+	 */
+	if (!writelist && xdr->page_len) {
+		ret = svc_rdma_send_xdr_pagelist(info, xdr);
+		if (ret < 0)
+			goto out_err;
+		consumed += xdr->page_len;
+	}
+
+	if (xdr->tail[0].iov_len) {
+		ret = svc_rdma_send_xdr_kvec(info, &xdr->tail[0]);
+		if (ret < 0)
+			goto out_err;
+		consumed += xdr->tail[0].iov_len;
+	}
+
+	ret = svc_rdma_post_chunk_ctxt(&info->wi_cc);
+	if (ret < 0)
+		goto out_err;
+	return consumed;
+
+out_err:
+	svc_rdma_write_info_free(info);
+	return ret;
+}