Index: sys/buf.h
===================================================================
RCS file: /home/ncvs/src/sys/sys/buf.h,v
retrieving revision 1.207
diff -p -u -r1.207 buf.h
--- sys/buf.h	28 Mar 2008 12:30:12 -0000	1.207
+++ sys/buf.h	2 Apr 2008 10:23:43 -0000
@@ -219,12 +219,12 @@ struct buf {
 #define	B_NEEDSGIANT	0x02000000	/* Buffer's vnode needs giant. */
 #define	B_PAGING	0x04000000	/* volatile paging I/O -- bypass VMIO */
 #define B_MANAGED	0x08000000	/* Managed by FS. */
-#define B_RAM		0x10000000	/* Read ahead mark (flag) */
+#define B_100000000	0x10000000	/* Available flag. */
 #define B_VMIO		0x20000000	/* VMIO flag */
 #define B_CLUSTER	0x40000000	/* pagein op, so swap() can count it */
 #define B_REMFREE	0x80000000	/* Delayed bremfree */
 
-#define PRINT_BUF_FLAGS "\20\40remfree\37cluster\36vmio\35ram\34b27" \
+#define PRINT_BUF_FLAGS "\20\40remfree\37cluster\36vmio\35b28\34paging" \
 	"\33paging\32b25\31b24\30b23\27relbuf\26dirty\25b20" \
 	"\24b19\23b18\22clusterok\21malloc\20nocache\17b14\16inval" \
 	"\15b12\14b11\13eintr\12done\11persist\10delwri\7validsuspwrt" \
Index: kern/vfs_cluster.c
===================================================================
RCS file: /home/ncvs/src/sys/kern/vfs_cluster.c,v
retrieving revision 1.177
diff -p -u -r1.177 vfs_cluster.c
--- kern/vfs_cluster.c	22 Mar 2008 09:15:14 -0000	1.177
+++ kern/vfs_cluster.c	2 Apr 2008 10:23:44 -0000
@@ -98,7 +98,6 @@ cluster_read(vp, filesize, lblkno, size,
 	daddr_t blkno, origblkno;
 	int maxra, racluster;
 	int error, ncontig;
-	int i;
 
 	error = 0;
 	bo = &vp->v_bufobj;
@@ -121,46 +120,21 @@ cluster_read(vp, filesize, lblkno, size,
 	origblkno = lblkno;
 
 	/*
-	 * if it is in the cache, then check to see if the reads have been
-	 * sequential.  If they have, then try some read-ahead, otherwise
-	 * back-off on prospective read-aheads.
+	 * if it is in the cache, then check to see if the next block is
+	 * also.  We initiate read-ahead when the next block is not availble
+	 * to achieve some concurrency while still doing optimal io sizes.
 	 */
 	if (bp->b_flags & B_CACHE) {
-		if (!seqcount) {
+		if (!seqcount)
 			return 0;
-		} else if ((bp->b_flags & B_RAM) == 0) {
+		lblkno++;
+		BO_LOCK(bo);
+		rbp = gbincore(&vp->v_bufobj, lblkno);
+		if (rbp != NULL && (rbp->b_flags & B_INVAL))
+			rbp = NULL;
+		BO_UNLOCK(bo);
+		if (rbp != NULL)
 			return 0;
-		} else {
-			bp->b_flags &= ~B_RAM;
-			BO_LOCK(bo);
-			for (i = 1; i < maxra; i++) {
-				/*
-				 * Stop if the buffer does not exist or it
-				 * is invalid (about to go away?)
-				 */
-				rbp = gbincore(&vp->v_bufobj, lblkno+i);
-				if (rbp == NULL || (rbp->b_flags & B_INVAL))
-					break;
-
-				/*
-				 * Set another read-ahead mark so we know 
-				 * to check again. (If we can lock the
-				 * buffer without waiting)
-				 */
-				if ((((i % racluster) == (racluster - 1)) ||
-				    (i == (maxra - 1))) 
-				    && (0 == BUF_LOCK(rbp, 
-					LK_EXCLUSIVE | LK_NOWAIT, NULL))) {
-					rbp->b_flags |= B_RAM;
-					BUF_UNLOCK(rbp);
-				}			
-			}
-			BO_UNLOCK(bo);
-			if (i >= maxra) {
-				return 0;
-			}
-			lblkno += i;
-		}
 		reqbp = bp = NULL;
 	/*
 	 * If it isn't in the cache, then get a chunk from
@@ -211,7 +185,6 @@ cluster_read(vp, filesize, lblkno, size,
 				blkno, size, nblks, bp);
 			lblkno += (bp->b_bufsize / size);
 		} else {
-			bp->b_flags |= B_RAM;
 			bp->b_iocmd = BIO_READ;
 			lblkno += 1;
 		}
@@ -265,7 +238,7 @@ cluster_read(vp, filesize, lblkno, size,
 				bqrelse(rbp);
 				continue;
 			}
-			rbp->b_flags |= B_ASYNC | B_RAM;
+			rbp->b_flags |= B_ASYNC;
 			rbp->b_iocmd = BIO_READ;
 			rbp->b_blkno = blkno;
 		}
@@ -330,7 +303,7 @@ cluster_rbuild(vp, filesize, lbn, blkno,
 		tbp = getblk(vp, lbn, size, 0, 0, 0);
 		if (tbp->b_flags & B_CACHE)
 			return tbp;
-		tbp->b_flags |= B_ASYNC | B_RAM;
+		tbp->b_flags |= B_ASYNC;
 		tbp->b_iocmd = BIO_READ;
 	}
 	tbp->b_blkno = blkno;
@@ -416,12 +389,6 @@ cluster_rbuild(vp, filesize, lbn, blkno,
 			}
 
 			/*
-			 * Set a read-ahead mark as appropriate
-			 */
-			if ((fbp && (i == 1)) || (i == (run - 1)))
-				tbp->b_flags |= B_RAM;
-
-			/*
 			 * Set the buffer up for an async read (XXX should
 			 * we do this only if we do not wind up brelse()ing?).
 			 * Set the block number if it isn't set, otherwise