Store a hint in the nfsnode to detect sequential access of the file.

Kick off a readahead only when sequential access is detected.  This
eliminates wasteful readaheads in random file access.

Submitted by:	Mohan Srinivasan mohans at yahoo-inc dot com
Obtained from:	Yahoo!

3 files changed, 6 insertions, 1 deletions

diff --git a/sys/nfsclient/nfs_bio.c b/sys/nfsclient/nfs_bio.c
index 9e9af49..c6eea93 100644
--- a/sys/nfsclient/nfs_bio.c
+++ b/sys/nfsclient/nfs_bio.c
@@ -421,8 +421,10 @@ nfs_bioread(struct vnode *vp, struct uio *uio, int ioflag, struct ucred *cred)
 
 		/*
 		 * Start the read ahead(s), as required.
+		 * The readahead is kicked off only if sequential access
+		 * is detected, based on the readahead hint (ra_expect_lbn).
 		 */
-		if (nmp->nm_readahead > 0) {
+		if (nmp->nm_readahead > 0 && np->ra_expect_lbn == lbn) {
 		    for (nra = 0; nra < nmp->nm_readahead && nra < seqcount &&
 			(off_t)(lbn + 1 + nra) * biosize < np->n_size; nra++) {
 			rabn = lbn + 1 + nra;
@@ -448,6 +450,7 @@ nfs_bioread(struct vnode *vp, struct uio *uio, int ioflag, struct ucred *cred)
 			    }
 			}
 		    }
+		    np->ra_expect_lbn = lbn + 1;
 		}
 
 		/*
diff --git a/sys/nfsclient/nfs_vnops.c b/sys/nfsclient/nfs_vnops.c
index 68f63fd..d7f9330 100644
--- a/sys/nfsclient/nfs_vnops.c
+++ b/sys/nfsclient/nfs_vnops.c
@@ -434,6 +434,7 @@ nfs_open(struct vop_open_args *ap)
 			np->n_mtime = vattr.va_mtime;
 		}
 	}
+	np->ra_expect_lbn = 0;
 	return (0);
 }
 
diff --git a/sys/nfsclient/nfsnode.h b/sys/nfsclient/nfsnode.h
index 4a4d835..9889ea4 100644
--- a/sys/nfsclient/nfsnode.h
+++ b/sys/nfsclient/nfsnode.h
@@ -126,6 +126,7 @@ struct nfsnode {
 	struct nfs4_fctx	n_wfc;
 	u_char			*n_name;	/* leaf name, for v4 OPEN op */
 	uint32_t		n_namelen;
+	daddr_t			ra_expect_lbn;
 };
 
 #define n_atim		n_un1.nf_atim