svcrdma: Persistently allocate and DMA-map Receive buffers

The current Receive path uses an array of pages which are allocated
and DMA mapped when each Receive WR is posted, and then handed off
to the upper layer in rqstp::rq_arg. The page flip releases unused
pages in the rq_pages pagelist. This mechanism introduces a
significant amount of overhead.

So instead, kmalloc the Receive buffer, and leave it DMA-mapped
while the transport remains connected. This confers a number of
benefits:

* Each Receive WR requires only one receive SGE, no matter how large
  the inline threshold is. This helps the server-side NFS/RDMA
  transport operate on less capable RDMA devices.

* The Receive buffer is left allocated and mapped all the time. This
  relieves svc_rdma_post_recv from the overhead of allocating and
  DMA-mapping a fresh buffer.

* svc_rdma_wc_receive no longer has to DMA unmap the Receive buffer.
  It has to DMA sync only the number of bytes that were received.

* svc_rdma_build_arg_xdr no longer has to free a page in rq_pages
  for each page in the Receive buffer, making it a constant-time
  function.

* The Receive buffer is now plugged directly into the rq_arg's
  head[0].iov_vec, and can be larger than a page without spilling
  over into rq_arg's page list. This enables simplification of
  the RDMA Read path in subsequent patches.

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

diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
index f0bd0b6d893180f07120687e254c1fcf9782fc9c..01baabfb863b4437f0d5c02abfd708d9f9cbe937 100644 (file)
--- a/include/linux/sunrpc/svc_rdma.h
+++ b/include/linux/sunrpc/svc_rdma.h
@@ -148,12 +148,12 @@ struct svc_rdma_recv_ctxt {
        struct list_head        rc_list;
        struct ib_recv_wr       rc_recv_wr;
        struct ib_cqe           rc_cqe;
+       struct ib_sge           rc_recv_sge;
+       void                    *rc_recv_buf;
        struct xdr_buf          rc_arg;
        u32                     rc_byte_len;
        unsigned int            rc_page_count;
        unsigned int            rc_hdr_count;
-       struct ib_sge           rc_sges[1 +
-                                       RPCRDMA_MAX_INLINE_THRESH / PAGE_SIZE];
        struct page             *rc_pages[RPCSVC_MAXPAGES];
 };
 

diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
index d9fef5211116e98aa81237a2389f756f6422df7f..d4ccd1c0142cb6984fd582fb341147c4a539900d 100644 (file)
--- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
@@ -117,6 +117,43 @@ svc_rdma_next_recv_ctxt(struct list_head *list)
                                        rc_list);
 }
 
+static struct svc_rdma_recv_ctxt *
+svc_rdma_recv_ctxt_alloc(struct svcxprt_rdma *rdma)
+{
+       struct svc_rdma_recv_ctxt *ctxt;
+       dma_addr_t addr;
+       void *buffer;
+
+       ctxt = kmalloc(sizeof(*ctxt), GFP_KERNEL);
+       if (!ctxt)
+               goto fail0;
+       buffer = kmalloc(rdma->sc_max_req_size, GFP_KERNEL);
+       if (!buffer)
+               goto fail1;
+       addr = ib_dma_map_single(rdma->sc_pd->device, buffer,
+                                rdma->sc_max_req_size, DMA_FROM_DEVICE);
+       if (ib_dma_mapping_error(rdma->sc_pd->device, addr))
+               goto fail2;
+
+       ctxt->rc_recv_wr.next = NULL;
+       ctxt->rc_recv_wr.wr_cqe = &ctxt->rc_cqe;
+       ctxt->rc_recv_wr.sg_list = &ctxt->rc_recv_sge;
+       ctxt->rc_recv_wr.num_sge = 1;
+       ctxt->rc_cqe.done = svc_rdma_wc_receive;
+       ctxt->rc_recv_sge.addr = addr;
+       ctxt->rc_recv_sge.length = rdma->sc_max_req_size;
+       ctxt->rc_recv_sge.lkey = rdma->sc_pd->local_dma_lkey;
+       ctxt->rc_recv_buf = buffer;
+       return ctxt;
+
+fail2:
+       kfree(buffer);
+fail1:
+       kfree(ctxt);
+fail0:
+       return NULL;
+}
+
 /**
  * svc_rdma_recv_ctxts_destroy - Release all recv_ctxt's for an xprt
  * @rdma: svcxprt_rdma being torn down
@@ -128,6 +165,11 @@ void svc_rdma_recv_ctxts_destroy(struct svcxprt_rdma *rdma)
 
        while ((ctxt = svc_rdma_next_recv_ctxt(&rdma->sc_recv_ctxts))) {
                list_del(&ctxt->rc_list);
+               ib_dma_unmap_single(rdma->sc_pd->device,
+                                   ctxt->rc_recv_sge.addr,
+                                   ctxt->rc_recv_sge.length,
+                                   DMA_FROM_DEVICE);
+               kfree(ctxt->rc_recv_buf);
                kfree(ctxt);
        }
 }
@@ -145,32 +187,18 @@ svc_rdma_recv_ctxt_get(struct svcxprt_rdma *rdma)
        spin_unlock(&rdma->sc_recv_lock);
 
 out:
-       ctxt->rc_recv_wr.num_sge = 0;
        ctxt->rc_page_count = 0;
        return ctxt;
 
 out_empty:
        spin_unlock(&rdma->sc_recv_lock);
 
-       ctxt = kmalloc(sizeof(*ctxt), GFP_KERNEL);
+       ctxt = svc_rdma_recv_ctxt_alloc(rdma);
        if (!ctxt)
                return NULL;
        goto out;
 }
 
-static void svc_rdma_recv_ctxt_unmap(struct svcxprt_rdma *rdma,
-                                    struct svc_rdma_recv_ctxt *ctxt)
-{
-       struct ib_device *device = rdma->sc_cm_id->device;
-       int i;
-
-       for (i = 0; i < ctxt->rc_recv_wr.num_sge; i++)
-               ib_dma_unmap_page(device,
-                                 ctxt->rc_sges[i].addr,
-                                 ctxt->rc_sges[i].length,
-                                 DMA_FROM_DEVICE);
-}
-
 /**
  * svc_rdma_recv_ctxt_put - Return recv_ctxt to free list
  * @rdma: controlling svcxprt_rdma
@@ -191,46 +219,14 @@ void svc_rdma_recv_ctxt_put(struct svcxprt_rdma *rdma,
 
 static int svc_rdma_post_recv(struct svcxprt_rdma *rdma)
 {
-       struct ib_device *device = rdma->sc_cm_id->device;
        struct svc_rdma_recv_ctxt *ctxt;
        struct ib_recv_wr *bad_recv_wr;
-       int sge_no, buflen, ret;
-       struct page *page;
-       dma_addr_t pa;
+       int ret;
 
        ctxt = svc_rdma_recv_ctxt_get(rdma);
        if (!ctxt)
                return -ENOMEM;
 
-       buflen = 0;
-       ctxt->rc_cqe.done = svc_rdma_wc_receive;
-       for (sge_no = 0; buflen < rdma->sc_max_req_size; sge_no++) {
-               if (sge_no >= rdma->sc_max_sge) {
-                       pr_err("svcrdma: Too many sges (%d)\n", sge_no);
-                       goto err_put_ctxt;
-               }
-
-               page = alloc_page(GFP_KERNEL);
-               if (!page)
-                       goto err_put_ctxt;
-               ctxt->rc_pages[sge_no] = page;
-               ctxt->rc_page_count++;
-
-               pa = ib_dma_map_page(device, ctxt->rc_pages[sge_no],
-                                    0, PAGE_SIZE, DMA_FROM_DEVICE);
-               if (ib_dma_mapping_error(device, pa))
-                       goto err_put_ctxt;
-               ctxt->rc_sges[sge_no].addr = pa;
-               ctxt->rc_sges[sge_no].length = PAGE_SIZE;
-               ctxt->rc_sges[sge_no].lkey = rdma->sc_pd->local_dma_lkey;
-               ctxt->rc_recv_wr.num_sge++;
-
-               buflen += PAGE_SIZE;
-       }
-       ctxt->rc_recv_wr.next = NULL;
-       ctxt->rc_recv_wr.sg_list = &ctxt->rc_sges[0];
-       ctxt->rc_recv_wr.wr_cqe = &ctxt->rc_cqe;
-
        svc_xprt_get(&rdma->sc_xprt);
        ret = ib_post_recv(rdma->sc_qp, &ctxt->rc_recv_wr, &bad_recv_wr);
        trace_svcrdma_post_recv(&ctxt->rc_recv_wr, ret);
@@ -238,12 +234,7 @@ static int svc_rdma_post_recv(struct svcxprt_rdma *rdma)
                goto err_post;
        return 0;
 
-err_put_ctxt:
-       svc_rdma_recv_ctxt_unmap(rdma, ctxt);
-       svc_rdma_recv_ctxt_put(rdma, ctxt);
-       return -ENOMEM;
 err_post:
-       svc_rdma_recv_ctxt_unmap(rdma, ctxt);
        svc_rdma_recv_ctxt_put(rdma, ctxt);
        svc_xprt_put(&rdma->sc_xprt);
        return ret;
@@ -289,7 +280,6 @@ static void svc_rdma_wc_receive(struct ib_cq *cq, struct ib_wc *wc)
 
        /* WARNING: Only wc->wr_cqe and wc->status are reliable */
        ctxt = container_of(cqe, struct svc_rdma_recv_ctxt, rc_cqe);
-       svc_rdma_recv_ctxt_unmap(rdma, ctxt);
 
        if (wc->status != IB_WC_SUCCESS)
                goto flushed;
@@ -299,6 +289,10 @@ static void svc_rdma_wc_receive(struct ib_cq *cq, struct ib_wc *wc)
 
        /* All wc fields are now known to be valid */
        ctxt->rc_byte_len = wc->byte_len;
+       ib_dma_sync_single_for_cpu(rdma->sc_pd->device,
+                                  ctxt->rc_recv_sge.addr,
+                                  wc->byte_len, DMA_FROM_DEVICE);
+
        spin_lock(&rdma->sc_rq_dto_lock);
        list_add_tail(&ctxt->rc_list, &rdma->sc_rq_dto_q);
        spin_unlock(&rdma->sc_rq_dto_lock);
@@ -339,64 +333,22 @@ void svc_rdma_flush_recv_queues(struct svcxprt_rdma *rdma)
        }
 }
 
-/*
- * Replace the pages in the rq_argpages array with the pages from the SGE in
- * the RDMA_RECV completion. The SGL should contain full pages up until the
- * last one.
- */
 static void svc_rdma_build_arg_xdr(struct svc_rqst *rqstp,
                                   struct svc_rdma_recv_ctxt *ctxt)
 {
-       struct page *page;
-       int sge_no;
-       u32 len;
-
-       /* The reply path assumes the Call's transport header resides
-        * in rqstp->rq_pages[0].
-        */
-       page = ctxt->rc_pages[0];
-       put_page(rqstp->rq_pages[0]);
-       rqstp->rq_pages[0] = page;
-
-       /* Set up the XDR head */
-       rqstp->rq_arg.head[0].iov_base = page_address(page);
-       rqstp->rq_arg.head[0].iov_len =
-               min_t(size_t, ctxt->rc_byte_len, ctxt->rc_sges[0].length);
-       rqstp->rq_arg.len = ctxt->rc_byte_len;
-       rqstp->rq_arg.buflen = ctxt->rc_byte_len;
-
-       /* Compute bytes past head in the SGL */
-       len = ctxt->rc_byte_len - rqstp->rq_arg.head[0].iov_len;
-
-       /* If data remains, store it in the pagelist */
-       rqstp->rq_arg.page_len = len;
-       rqstp->rq_arg.page_base = 0;
-
-       sge_no = 1;
-       while (len && sge_no < ctxt->rc_recv_wr.num_sge) {
-               page = ctxt->rc_pages[sge_no];
-               put_page(rqstp->rq_pages[sge_no]);
-               rqstp->rq_pages[sge_no] = page;
-               len -= min_t(u32, len, ctxt->rc_sges[sge_no].length);
-               sge_no++;
-       }
-       ctxt->rc_hdr_count = sge_no;
-       rqstp->rq_respages = &rqstp->rq_pages[sge_no];
+       struct xdr_buf *arg = &rqstp->rq_arg;
+
+       arg->head[0].iov_base = ctxt->rc_recv_buf;
+       arg->head[0].iov_len = ctxt->rc_byte_len;
+       arg->tail[0].iov_base = NULL;
+       arg->tail[0].iov_len = 0;
+       arg->page_len = 0;
+       arg->page_base = 0;
+       arg->buflen = ctxt->rc_byte_len;
+       arg->len = ctxt->rc_byte_len;
+
+       rqstp->rq_respages = &rqstp->rq_pages[0];
        rqstp->rq_next_page = rqstp->rq_respages + 1;
-
-       /* If not all pages were used from the SGL, free the remaining ones */
-       while (sge_no < ctxt->rc_recv_wr.num_sge) {
-               page = ctxt->rc_pages[sge_no++];
-               put_page(page);
-       }
-
-       /* @ctxt's pages have all been released or moved to @rqstp->rq_pages.
-        */
-       ctxt->rc_page_count = 0;
-
-       /* Set up tail */
-       rqstp->rq_arg.tail[0].iov_base = NULL;
-       rqstp->rq_arg.tail[0].iov_len = 0;
 }
 
 /* This accommodates the largest possible Write chunk,

diff --git a/net/sunrpc/xprtrdma/svc_rdma_rw.c b/net/sunrpc/xprtrdma/svc_rdma_rw.c
index 8242aa318ac193653ac2d3e7e9d2726e7edc7d2c..ce3ea8419704839cc48c050a134070ac3a7a864f 100644 (file)
--- a/net/sunrpc/xprtrdma/svc_rdma_rw.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_rw.c
@@ -718,15 +718,14 @@ static int svc_rdma_build_normal_read_chunk(struct svc_rqst *rqstp,
        struct svc_rdma_recv_ctxt *head = info->ri_readctxt;
        int ret;
 
-       info->ri_pageno = head->rc_hdr_count;
-       info->ri_pageoff = 0;
-
        ret = svc_rdma_build_read_chunk(rqstp, info, p);
        if (ret < 0)
                goto out;
 
        trace_svcrdma_encode_read(info->ri_chunklen, info->ri_position);
 
+       head->rc_hdr_count = 0;
+
        /* Split the Receive buffer between the head and tail
         * buffers at Read chunk's position. XDR roundup of the
         * chunk is not included in either the pagelist or in
@@ -775,9 +774,6 @@ static int svc_rdma_build_pz_read_chunk(struct svc_rqst *rqstp,
        struct svc_rdma_recv_ctxt *head = info->ri_readctxt;
        int ret;
 
-       info->ri_pageno = head->rc_hdr_count - 1;
-       info->ri_pageoff = offset_in_page(head->rc_byte_len);
-
        ret = svc_rdma_build_read_chunk(rqstp, info, p);
        if (ret < 0)
                goto out;
@@ -787,20 +783,13 @@ static int svc_rdma_build_pz_read_chunk(struct svc_rqst *rqstp,
        head->rc_arg.len += info->ri_chunklen;
        head->rc_arg.buflen += info->ri_chunklen;
 
-       if (head->rc_arg.buflen <= head->rc_sges[0].length) {
-               /* Transport header and RPC message fit entirely
-                * in page where head iovec resides.
-                */
-               head->rc_arg.head[0].iov_len = info->ri_chunklen;
-       } else {
-               /* Transport header and part of RPC message reside
-                * in the head iovec's page.
-                */
-               head->rc_arg.head[0].iov_len =
-                       head->rc_sges[0].length - head->rc_byte_len;
-               head->rc_arg.page_len =
-                       info->ri_chunklen - head->rc_arg.head[0].iov_len;
-       }
+       head->rc_hdr_count = 1;
+       head->rc_arg.head[0].iov_base = page_address(head->rc_pages[0]);
+       head->rc_arg.head[0].iov_len = min_t(size_t, PAGE_SIZE,
+                                            info->ri_chunklen);
+
+       head->rc_arg.page_len = info->ri_chunklen -
+                               head->rc_arg.head[0].iov_len;
 
 out:
        return ret;
@@ -834,7 +823,6 @@ int svc_rdma_recv_read_chunk(struct svcxprt_rdma *rdma, struct svc_rqst *rqstp,
         * head->rc_arg. Pages involved with RDMA Read I/O are
         * transferred there.
         */
-       head->rc_page_count = head->rc_hdr_count;
        head->rc_arg.head[0] = rqstp->rq_arg.head[0];
        head->rc_arg.tail[0] = rqstp->rq_arg.tail[0];
        head->rc_arg.pages = head->rc_pages;
@@ -847,6 +835,8 @@ int svc_rdma_recv_read_chunk(struct svcxprt_rdma *rdma, struct svc_rqst *rqstp,
        if (!info)
                return -ENOMEM;
        info->ri_readctxt = head;
+       info->ri_pageno = 0;
+       info->ri_pageoff = 0;
 
        info->ri_position = be32_to_cpup(p + 1);
        if (info->ri_position)

diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
index cbbde70eeec5433c5851e28e2cc32fcfc35dd230..b27b597d94da921d51321536a1f306c7b987be45 100644 (file)
--- a/net/sunrpc/xprtrdma/svc_rdma_sendto.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
@@ -629,10 +629,7 @@ int svc_rdma_sendto(struct svc_rqst *rqstp)
        struct page *res_page;
        int ret;
 
-       /* Find the call's chunk lists to decide how to send the reply.
-        * Receive places the Call's xprt header at the start of page 0.
-        */
-       rdma_argp = page_address(rqstp->rq_pages[0]);
+       rdma_argp = rctxt->rc_recv_buf;
        svc_rdma_get_write_arrays(rdma_argp, &wr_lst, &rp_ch);
 
        /* Create the RDMA response header. xprt->xpt_mutex,

diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
index ef32c46a234c6d1ea95e374639590822a27d5bab..baeecbb2f763a32c42b7cb04ef3a49d576599b9a 100644 (file)
--- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
@@ -669,7 +669,7 @@ static struct svc_xprt *svc_rdma_accept(struct svc_xprt *xprt)
        qp_attr.cap.max_send_wr = newxprt->sc_sq_depth - ctxts;
        qp_attr.cap.max_recv_wr = rq_depth;
        qp_attr.cap.max_send_sge = newxprt->sc_max_sge;
-       qp_attr.cap.max_recv_sge = newxprt->sc_max_sge;
+       qp_attr.cap.max_recv_sge = 1;
        qp_attr.sq_sig_type = IB_SIGNAL_REQ_WR;
        qp_attr.qp_type = IB_QPT_RC;
        qp_attr.send_cq = newxprt->sc_sq_cq;