nfs: add new tracepoint for pnfs_update_layout

pnfs_update_layout is really the "nexus" of layout handling. If it
returns NULL then we end up going through the MDS. This patch adds
some tracepoints to that function that allow us to determine the
cause when we end up going through the MDS unexpectedly.

Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

1 files changed, 32 insertions, 6 deletions

diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
index bec0384499f7..1489065bb051 100644
--- a/fs/nfs/pnfs.c
+++ b/fs/nfs/pnfs.c
@@ -1520,14 +1520,23 @@ pnfs_update_layout(struct inode *ino,
 	struct pnfs_layout_segment *lseg = NULL;
 	bool first;
 
-	if (!pnfs_enabled_sb(NFS_SERVER(ino)))
+	if (!pnfs_enabled_sb(NFS_SERVER(ino))) {
+		trace_pnfs_update_layout(ino, pos, count, iomode, lseg,
+				 PNFS_UPDATE_LAYOUT_NO_PNFS);
 		goto out;
+	}
 
-	if (iomode == IOMODE_READ && i_size_read(ino) == 0)
+	if (iomode == IOMODE_READ && i_size_read(ino) == 0) {
+		trace_pnfs_update_layout(ino, pos, count, iomode, lseg,
+				 PNFS_UPDATE_LAYOUT_RD_ZEROLEN);
 		goto out;
+	}
 
-	if (pnfs_within_mdsthreshold(ctx, ino, iomode))
+	if (pnfs_within_mdsthreshold(ctx, ino, iomode)) {
+		trace_pnfs_update_layout(ino, pos, count, iomode, lseg,
+				 PNFS_UPDATE_LAYOUT_MDSTHRESH);
 		goto out;
+	}
 
 lookup_again:
 	first = false;
@@ -1535,19 +1544,26 @@ lookup_again:
 	lo = pnfs_find_alloc_layout(ino, ctx, gfp_flags);
 	if (lo == NULL) {
 		spin_unlock(&ino->i_lock);
+		trace_pnfs_update_layout(ino, pos, count, iomode, lseg,
+				 PNFS_UPDATE_LAYOUT_NOMEM);
 		goto out;
 	}
 
 	/* Do we even need to bother with this? */
 	if (test_bit(NFS_LAYOUT_BULK_RECALL, &lo->plh_flags)) {
+		trace_pnfs_update_layout(ino, pos, count, iomode, lseg,
+				 PNFS_UPDATE_LAYOUT_BULK_RECALL);
 		dprintk("%s matches recall, use MDS\n", __func__);
 		goto out_unlock;
 	}
 
 	/* if LAYOUTGET already failed once we don't try again */
 	if (pnfs_layout_io_test_failed(lo, iomode) &&
-	    !pnfs_should_retry_layoutget(lo))
+	    !pnfs_should_retry_layoutget(lo)) {
+		trace_pnfs_update_layout(ino, pos, count, iomode, lseg,
+				 PNFS_UPDATE_LAYOUT_IO_TEST_FAIL);
 		goto out_unlock;
+	}
 
 	first = list_empty(&lo->plh_segs);
 	if (first) {
@@ -1567,8 +1583,11 @@ lookup_again:
 		 * already exists
 		 */
 		lseg = pnfs_find_lseg(lo, &arg);
-		if (lseg)
+		if (lseg) {
+			trace_pnfs_update_layout(ino, pos, count, iomode, lseg,
+					PNFS_UPDATE_LAYOUT_FOUND_CACHED);
 			goto out_unlock;
+		}
 	}
 
 	/*
@@ -1585,11 +1604,16 @@ lookup_again:
 			dprintk("%s retrying\n", __func__);
 			goto lookup_again;
 		}
+		trace_pnfs_update_layout(ino, pos, count, iomode, lseg,
+				PNFS_UPDATE_LAYOUT_RETURN);
 		goto out_put_layout_hdr;
 	}
 
-	if (pnfs_layoutgets_blocked(lo))
+	if (pnfs_layoutgets_blocked(lo)) {
+		trace_pnfs_update_layout(ino, pos, count, iomode, lseg,
+				PNFS_UPDATE_LAYOUT_BLOCKED);
 		goto out_unlock;
+	}
 	atomic_inc(&lo->plh_outstanding);
 	spin_unlock(&ino->i_lock);
 
@@ -1614,6 +1638,8 @@ lookup_again:
 	lseg = send_layoutget(lo, ctx, &arg, gfp_flags);
 	pnfs_clear_retry_layoutget(lo);
 	atomic_dec(&lo->plh_outstanding);
+	trace_pnfs_update_layout(ino, pos, count, iomode, lseg,
+				 PNFS_UPDATE_LAYOUT_SEND_LAYOUTGET);
 out_put_layout_hdr:
 	if (first)
 		pnfs_clear_first_layoutget(lo);