SUNRPC: Add trace event that reports reply page vector alignment

We don't want READ payloads that are partially in the head iovec and
in the page buffer because this requires pull-up, which can be
expensive.

The NFS/RPC client tries hard to predict the size of the head iovec
so that the incoming READ data payload lands only in the page
vector, but it doesn't always get it right. To help diagnose such
problems, add a trace point in the logic that decodes READ-like
operations that reports whether pull-up is being done.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

1 files changed, 27 insertions, 6 deletions

diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
index 6d0b615a02ae..5f0aa53fa4ae 100644
--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -347,13 +347,15 @@ EXPORT_SYMBOL_GPL(_copy_from_pages);
  * 'len' bytes. The extra data is not lost, but is instead
  * moved into the inlined pages and/or the tail.
  */
-static void
+static unsigned int
 xdr_shrink_bufhead(struct xdr_buf *buf, size_t len)
 {
 	struct kvec *head, *tail;
 	size_t copy, offs;
 	unsigned int pglen = buf->page_len;
+	unsigned int result;
 
+	result = 0;
 	tail = buf->tail;
 	head = buf->head;
 
@@ -367,6 +369,7 @@ xdr_shrink_bufhead(struct xdr_buf *buf, size_t len)
 			copy = tail->iov_len - len;
 			memmove((char *)tail->iov_base + len,
 					tail->iov_base, copy);
+			result += copy;
 		}
 		/* Copy from the inlined pages into the tail */
 		copy = len;
@@ -377,11 +380,13 @@ xdr_shrink_bufhead(struct xdr_buf *buf, size_t len)
 			copy = 0;
 		else if (copy > tail->iov_len - offs)
 			copy = tail->iov_len - offs;
-		if (copy != 0)
+		if (copy != 0) {
 			_copy_from_pages((char *)tail->iov_base + offs,
 					buf->pages,
 					buf->page_base + pglen + offs - len,
 					copy);
+			result += copy;
+		}
 		/* Do we also need to copy data from the head into the tail ? */
 		if (len > pglen) {
 			offs = copy = len - pglen;
@@ -391,6 +396,7 @@ xdr_shrink_bufhead(struct xdr_buf *buf, size_t len)
 					(char *)head->iov_base +
 					head->iov_len - offs,
 					copy);
+			result += copy;
 		}
 	}
 	/* Now handle pages */
@@ -406,12 +412,15 @@ xdr_shrink_bufhead(struct xdr_buf *buf, size_t len)
 		_copy_to_pages(buf->pages, buf->page_base,
 				(char *)head->iov_base + head->iov_len - len,
 				copy);
+		result += copy;
 	}
 	head->iov_len -= len;
 	buf->buflen -= len;
 	/* Have we truncated the message? */
 	if (buf->len > buf->buflen)
 		buf->len = buf->buflen;
+
+	return result;
 }
 
 /**
@@ -423,14 +432,16 @@ xdr_shrink_bufhead(struct xdr_buf *buf, size_t len)
  * 'len' bytes. The extra data is not lost, but is instead
  * moved into the tail.
  */
-static void
+static unsigned int
 xdr_shrink_pagelen(struct xdr_buf *buf, size_t len)
 {
 	struct kvec *tail;
 	size_t copy;
 	unsigned int pglen = buf->page_len;
 	unsigned int tailbuf_len;
+	unsigned int result;
 
+	result = 0;
 	tail = buf->tail;
 	BUG_ON (len > pglen);
 
@@ -448,18 +459,22 @@ xdr_shrink_pagelen(struct xdr_buf *buf, size_t len)
 		if (tail->iov_len > len) {
 			char *p = (char *)tail->iov_base + len;
 			memmove(p, tail->iov_base, tail->iov_len - len);
+			result += tail->iov_len - len;
 		} else
 			copy = tail->iov_len;
 		/* Copy from the inlined pages into the tail */
 		_copy_from_pages((char *)tail->iov_base,
 				buf->pages, buf->page_base + pglen - len,
 				copy);
+		result += copy;
 	}
 	buf->page_len -= len;
 	buf->buflen -= len;
 	/* Have we truncated the message? */
 	if (buf->len > buf->buflen)
 		buf->len = buf->buflen;
+
+	return result;
 }
 
 void
@@ -959,13 +974,17 @@ static unsigned int xdr_align_pages(struct xdr_stream *xdr, unsigned int len)
 	struct kvec *iov;
 	unsigned int nwords = XDR_QUADLEN(len);
 	unsigned int cur = xdr_stream_pos(xdr);
+	unsigned int copied, offset;
 
 	if (xdr->nwords == 0)
 		return 0;
+
 	/* Realign pages to current pointer position */
-	iov  = buf->head;
+	iov = buf->head;
 	if (iov->iov_len > cur) {
-		xdr_shrink_bufhead(buf, iov->iov_len - cur);
+		offset = iov->iov_len - cur;
+		copied = xdr_shrink_bufhead(buf, offset);
+		trace_rpc_xdr_alignment(xdr, offset, copied);
 		xdr->nwords = XDR_QUADLEN(buf->len - cur);
 	}
 
@@ -977,7 +996,9 @@ static unsigned int xdr_align_pages(struct xdr_stream *xdr, unsigned int len)
 		len = buf->page_len;
 	else if (nwords < xdr->nwords) {
 		/* Truncate page data and move it into the tail */
-		xdr_shrink_pagelen(buf, buf->page_len - len);
+		offset = buf->page_len - len;
+		copied = xdr_shrink_pagelen(buf, offset);
+		trace_rpc_xdr_alignment(xdr, offset, copied);
 		xdr->nwords = XDR_QUADLEN(buf->len - cur);
 	}
 	return len;