Reviewed by: Many at differnt times in differnt parts,

		including alan, john, me, luoqi, and kirk
Submitted by:	Matt Dillon <dillon@frebsd.org>

This change implements a relatively sophisticated fix to getnewbuf().
There were two problems with getnewbuf(). First, the writerecursion
can lead to a system stack overflow when you have NFS and/or VN
devices in the system. Second, the free/dirty buffer accounting was
completely broken. Not only did the nfs routines blow it trying to
manually account for the buffer state, but the accounting that was
done did not work well with the purpose of their existance: figuring
out when getnewbuf() needs to sleep.

The meat of the change is to kern/vfs_bio.c. The remaining diffs are
all minor except for NFS, which includes both the fixes for bp
interaction AND fixes for a 'biodone(): buffer already done' lockup.
Sys/buf.h also contains a chaining structure which is not used by
this patchset but is used by other patches that are coming soon.
This patch deliniated by tags PRE_MAT_GETBUF and POST_MAT_GETBUF.
(sorry for the missing T matt)

1 files changed, 660 insertions, 376 deletions

diff --git a/sys/kern/vfs_bio.c b/sys/kern/vfs_bio.c
index a01230b..76f14b2 100644
--- a/sys/kern/vfs_bio.c
+++ b/sys/kern/vfs_bio.c
@@ -11,7 +11,7 @@
  * 2. Absolutely no warranty of function or purpose is made by the author
  *		John S. Dyson.
  *
- * $Id: vfs_bio.c,v 1.200 1999/03/02 20:26:39 julian Exp $
+ * $Id: vfs_bio.c,v 1.201 1999/03/02 21:23:38 julian Exp $
  */
 
 /*
@@ -83,8 +83,7 @@ static void vfs_clean_pages(struct buf * bp);
 static void vfs_setdirty(struct buf *bp);
 static void vfs_vmio_release(struct buf *bp);
 static void flushdirtybuffers(int slpflag, int slptimeo);
-
-int needsbuffer;
+static int flushbufqueues(void);
 
 /*
  * Internal update daemon, process 3
@@ -92,11 +91,6 @@ int needsbuffer;
  */
 int vfs_update_wakeup;
 
-
-/*
- * buffers base kva
- */
-
 /*
  * bogus page -- for I/O to/from partially complete buffers
  * this is a temporary solution to the problem, but it is not
@@ -105,12 +99,13 @@ int vfs_update_wakeup;
  * but the code is intricate enough already.
  */
 vm_page_t bogus_page;
+int runningbufspace;
 static vm_offset_t bogus_offset;
 
 static int bufspace, maxbufspace, vmiospace, maxvmiobufspace,
-	bufmallocspace, maxbufmallocspace;
-int numdirtybuffers;
-static int lodirtybuffers, hidirtybuffers;
+	bufmallocspace, maxbufmallocspace, hibufspace;
+static int needsbuffer;
+static int numdirtybuffers, lodirtybuffers, hidirtybuffers;
 static int numfreebuffers, lofreebuffers, hifreebuffers;
 static int kvafreespace;
 
@@ -126,8 +121,12 @@ SYSCTL_INT(_vfs, OID_AUTO, lofreebuffers, CTLFLAG_RW,
 	&lofreebuffers, 0, "");
 SYSCTL_INT(_vfs, OID_AUTO, hifreebuffers, CTLFLAG_RW,
 	&hifreebuffers, 0, "");
+SYSCTL_INT(_vfs, OID_AUTO, runningbufspace, CTLFLAG_RD,
+	&runningbufspace, 0, "");
 SYSCTL_INT(_vfs, OID_AUTO, maxbufspace, CTLFLAG_RW,
 	&maxbufspace, 0, "");
+SYSCTL_INT(_vfs, OID_AUTO, hibufspace, CTLFLAG_RD,
+	&hibufspace, 0, "");
 SYSCTL_INT(_vfs, OID_AUTO, bufspace, CTLFLAG_RD,
 	&bufspace, 0, "");
 SYSCTL_INT(_vfs, OID_AUTO, maxvmiobufspace, CTLFLAG_RW,
@@ -146,11 +145,81 @@ struct bqueues bufqueues[BUFFER_QUEUES] = { { 0 } };
 
 extern int vm_swap_size;
 
-#define BUF_MAXUSE 24
+#define BUF_MAXUSE		24
+
+#define VFS_BIO_NEED_ANY	0x01	/* any freeable buffer */
+#define VFS_BIO_NEED_RESERVED02	0x02	/* unused */
+#define VFS_BIO_NEED_FREE	0x04	/* wait for free bufs, hi hysteresis */
+#define VFS_BIO_NEED_BUFSPACE	0x08	/* wait for buf space, lo hysteresis */
+#define VFS_BIO_NEED_KVASPACE	0x10	/* wait for buffer_map space, emerg  */
 
-#define VFS_BIO_NEED_ANY 1
-#define VFS_BIO_NEED_LOWLIMIT 2
-#define VFS_BIO_NEED_FREE 4
+/*
+ *	kvaspacewakeup:
+ *
+ *	Called when kva space is potential available for recovery or when
+ *	kva space is recovered in the buffer_map.  This function wakes up
+ *	anyone waiting for buffer_map kva space.  Even though the buffer_map
+ *	is larger then maxbufspace, this situation will typically occur 
+ *	when the buffer_map gets fragmented.
+ */
+
+static __inline void
+kvaspacewakeup(void)
+{
+	/*
+	 * If someone is waiting for KVA space, wake them up.  Even
+	 * though we haven't freed the kva space yet, the waiting
+	 * process will be able to now.
+	 */
+	if (needsbuffer & VFS_BIO_NEED_KVASPACE) {
+		needsbuffer &= ~VFS_BIO_NEED_KVASPACE;
+		wakeup(&needsbuffer);
+	}
+}
+
+/*
+ *	bufspacewakeup:
+ *
+ *	Called when buffer space is potentially available for recovery or when
+ *	buffer space is recovered.  getnewbuf() will block on this flag when
+ *	it is unable to free sufficient buffer space.  Buffer space becomes
+ *	recoverable when bp's get placed back in the queues.
+ */
+
+static __inline void
+bufspacewakeup(void)
+{
+	/*
+	 * If someone is waiting for BUF space, wake them up.  Even
+	 * though we haven't freed the kva space yet, the waiting
+	 * process will be able to now.
+	 */
+	if (needsbuffer & VFS_BIO_NEED_BUFSPACE) {
+		needsbuffer &= ~VFS_BIO_NEED_BUFSPACE;
+		wakeup(&needsbuffer);
+	}
+}
+
+/*
+ *	bufcountwakeup:
+ *
+ *	Called when a buffer has been added to one of the free queues to
+ *	account for the buffer and to wakeup anyone waiting for free buffers.
+ *	This typically occurs when large amounts of metadata are being handled
+ *	by the buffer cache ( else buffer space runs out first, usually ).
+ */
+
+static __inline void
+bufcountwakeup(void) 
+{
+	++numfreebuffers;
+	if (needsbuffer) {
+		needsbuffer &= ~VFS_BIO_NEED_ANY;
+		if (numfreebuffers >= hifreebuffers)
+			needsbuffer &= ~VFS_BIO_NEED_FREE;
+		wakeup(&needsbuffer);
+	}
+}
 
 /*
  * Initialize buffer headers and related structures.
@@ -186,17 +255,25 @@ bufinit()
 		TAILQ_INSERT_TAIL(&bufqueues[QUEUE_EMPTY], bp, b_freelist);
 		LIST_INSERT_HEAD(&invalhash, bp, b_hash);
 	}
-/*
- * maxbufspace is currently calculated to support all filesystem blocks
- * to be 8K.  If you happen to use a 16K filesystem, the size of the buffer
- * cache is still the same as it would be for 8K filesystems.  This
- * keeps the size of the buffer cache "in check" for big block filesystems.
- */
+
+	/*
+	 * maxbufspace is currently calculated to support all filesystem 
+	 * blocks to be 8K.  If you happen to use a 16K filesystem, the size
+	 * of the buffer cache is still the same as it would be for 8K 
+	 * filesystems.  This keeps the size of the buffer cache "in check" 
+	 * for big block filesystems.
+	 *
+	 * maxbufspace is calculated as around 50% of the KVA available in
+	 * the buffer_map ( DFLTSIZE vs BKVASIZE ), I presume to reduce the 
+	 * effect of fragmentation.
+	 */
 	maxbufspace = (nbuf + 8) * DFLTBSIZE;
+	if ((hibufspace = maxbufspace - MAXBSIZE * 5) <= MAXBSIZE)
+		hibufspace = 3 * maxbufspace / 4;
 /*
  * reserve 1/3 of the buffers for metadata (VDIR) which might not be VMIO'ed
  */
-	maxvmiobufspace = 2 * maxbufspace / 3;
+	maxvmiobufspace = 2 * hibufspace / 3;
 /*
  * Limit the amount of malloc memory since it is wired permanently into
  * the kernel space.  Even though this is accounted for in the buffer
@@ -204,18 +281,24 @@ bufinit()
  * The malloc scheme improves memory utilization significantly on average
  * (small) directories.
  */
-	maxbufmallocspace = maxbufspace / 20;
+	maxbufmallocspace = hibufspace / 20;
 
 /*
- * Remove the probability of deadlock conditions by limiting the
- * number of dirty buffers.
+ * Reduce the chance of a deadlock occuring by limiting the number
+ * of delayed-write dirty buffers we allow to stack up.
  */
-	hidirtybuffers = nbuf / 8 + 20;
 	lodirtybuffers = nbuf / 16 + 10;
+	hidirtybuffers = nbuf / 8 + 20;
 	numdirtybuffers = 0;
+
+/*
+ * Try to keep the number of free buffers in the specified range,
+ * and give the syncer access to an emergency reserve.
+ */
 	lofreebuffers = nbuf / 18 + 5;
 	hifreebuffers = 2 * lofreebuffers;
 	numfreebuffers = nbuf;
+
 	kvafreespace = 0;
 
 	bogus_offset = kmem_alloc_pageable(kernel_map, PAGE_SIZE);
@@ -233,24 +316,26 @@ bufinit()
 static void
 bfreekva(struct buf * bp)
 {
-	if (bp->b_kvasize == 0)
-		return;
-		
-	vm_map_delete(buffer_map,
-		(vm_offset_t) bp->b_kvabase,
-		(vm_offset_t) bp->b_kvabase + bp->b_kvasize);
-
-	bp->b_kvasize = 0;
-
+	if (bp->b_kvasize) {
+		vm_map_delete(buffer_map,
+		    (vm_offset_t) bp->b_kvabase,
+		    (vm_offset_t) bp->b_kvabase + bp->b_kvasize
+		);
+		bp->b_kvasize = 0;
+		kvaspacewakeup();
+	}
 }
 
 /*
- * remove the buffer from the appropriate free list
+ *	bremfree:
+ *
+ *	Remove the buffer from the appropriate free list.
  */
 void
 bremfree(struct buf * bp)
 {
 	int s = splbio();
+	int old_qindex = bp->b_qindex;
 
 	if (bp->b_qindex != QUEUE_NONE) {
 		if (bp->b_qindex == QUEUE_EMPTY) {
@@ -258,14 +343,29 @@ bremfree(struct buf * bp)
 		}
 		TAILQ_REMOVE(&bufqueues[bp->b_qindex], bp, b_freelist);
 		bp->b_qindex = QUEUE_NONE;
+		runningbufspace += bp->b_bufsize;
 	} else {
 #if !defined(MAX_PERF)
 		panic("bremfree: removing a buffer when not on a queue");
 #endif
 	}
-	if ((bp->b_flags & B_INVAL) ||
-		(bp->b_flags & (B_DELWRI|B_LOCKED)) == 0)
-		--numfreebuffers;
+
+	/*
+	 * Fixup numfreebuffers count.  If the buffer is invalid or not
+	 * delayed-write, and it was on the EMPTY, LRU, or AGE queues,
+	 * the buffer was free and we must decrement numfreebuffers.
+	 */
+	if ((bp->b_flags & B_INVAL) || (bp->b_flags & B_DELWRI) == 0) {
+		switch(old_qindex) {
+		case QUEUE_EMPTY:
+		case QUEUE_LRU:
+		case QUEUE_AGE:
+			--numfreebuffers;
+			break;
+		default:
+			break;
+		}
+	}
 	splx(s);
 }
 
@@ -286,6 +386,7 @@ bread(struct vnode * vp, daddr_t blkno, int size, struct ucred * cred,
 	if ((bp->b_flags & B_CACHE) == 0) {
 		if (curproc != NULL)
 			curproc->p_stats->p_ru.ru_inblock++;
+		KASSERT(!(bp->b_flags & B_ASYNC), ("bread: illegal async bp %p", bp));
 		bp->b_flags |= B_READ;
 		bp->b_flags &= ~(B_DONE | B_ERROR | B_INVAL);
 		if (bp->b_rcred == NOCRED) {
@@ -330,6 +431,7 @@ breadn(struct vnode * vp, daddr_t blkno, int size,
 		VOP_STRATEGY(vp, bp);
 		++readwait;
 	}
+
 	for (i = 0; i < cnt; i++, rablkno++, rabsize++) {
 		if (inmem(vp, *rablkno))
 			continue;
@@ -369,7 +471,6 @@ bwrite(struct buf * bp)
 	struct vnode *vp;
 	struct mount *mp;
 
-
 	if (bp->b_flags & B_INVAL) {
 		brelse(bp);
 		return (0);
@@ -381,16 +482,12 @@ bwrite(struct buf * bp)
 	if ((bp->b_flags & B_BUSY) == 0)
 		panic("bwrite: buffer is not busy???");
 #endif
+	s = splbio();
+	bundirty(bp);
 
-	bp->b_flags &= ~(B_READ | B_DONE | B_ERROR | B_DELWRI);
+	bp->b_flags &= ~(B_READ | B_DONE | B_ERROR);
 	bp->b_flags |= B_WRITEINPROG;
 
-	s = splbio();
-	if ((oldflags & B_DELWRI) == B_DELWRI) {
-		--numdirtybuffers;
-		reassignbuf(bp, bp->b_vp);
-	}
-
 	bp->b_vp->v_numoutput++;
 	vfs_busy_pages(bp, 1);
 	if (curproc != NULL)
@@ -420,23 +517,8 @@ bwrite(struct buf * bp)
 		brelse(bp);
 		return (rtval);
 	}
-	return (0);
-}
 
-void
-vfs_bio_need_satisfy(void) {
-	++numfreebuffers;
-	if (!needsbuffer)
-		return;
-	if (numdirtybuffers < lodirtybuffers) {
-		needsbuffer &= ~(VFS_BIO_NEED_ANY | VFS_BIO_NEED_LOWLIMIT);
-	} else {
-		needsbuffer &= ~VFS_BIO_NEED_ANY;
-	}
-	if (numfreebuffers >= hifreebuffers) {
-		needsbuffer &= ~VFS_BIO_NEED_FREE;
-	}
-	wakeup(&needsbuffer);
+	return (0);
 }
 
 /*
@@ -457,12 +539,7 @@ bdwrite(struct buf * bp)
 		brelse(bp);
 		return;
 	}
-	bp->b_flags &= ~(B_READ|B_RELBUF);
-	if ((bp->b_flags & B_DELWRI) == 0) {
-		bp->b_flags |= B_DONE | B_DELWRI;
-		reassignbuf(bp, bp->b_vp);
-		++numdirtybuffers;
-	}
+	bdirty(bp);
 
 	/*
 	 * This bmap keeps the system from needing to do the bmap later,
@@ -506,32 +583,68 @@ bdwrite(struct buf * bp)
 
 	if (numdirtybuffers >= hidirtybuffers)
 		flushdirtybuffers(0, 0);
-
-	return;
 }
 
-
 /*
- * Same as first half of bdwrite, mark buffer dirty, but do not release it.
- * Check how this compares with vfs_setdirty(); XXX [JRE]
+ *	bdirty:
+ *
+ *	Turn buffer into delayed write request.  We must clear B_READ and
+ *	B_RELBUF, and we must set B_DELWRI.  We reassign the buffer to 
+ *	itself to properly update it in the dirty/clean lists.  We mark it
+ *	B_DONE to ensure that any asynchronization of the buffer properly
+ *	clears B_DONE ( else a panic will occur later ).  Note that B_INVALID 
+ *	buffers are not considered dirty even if B_DELWRI is set.	
+ *
+ *	Since the buffer is not on a queue, we do not update the numfreebuffers
+ *	count.
+ *
+ *	Must be called at splbio().
+ *	The buffer must be on QUEUE_NONE.
  */
 void
 bdirty(bp)
-      struct buf *bp;
+	struct buf *bp;
 {
-	
-	bp->b_flags &= ~(B_READ|B_RELBUF); /* XXX ??? check this */
+	KASSERT(bp->b_qindex == QUEUE_NONE, ("bdirty: buffer %p still on queue %d", bp, bp->b_qindex));
+	bp->b_flags &= ~(B_READ|B_RELBUF);
+
 	if ((bp->b_flags & B_DELWRI) == 0) {
-		bp->b_flags |= B_DONE | B_DELWRI; /* why done? XXX JRE */
+		bp->b_flags |= B_DONE | B_DELWRI;
 		reassignbuf(bp, bp->b_vp);
 		++numdirtybuffers;
 	}
 }
 
 /*
- * Asynchronous write.
- * Start output on a buffer, but do not wait for it to complete.
- * The buffer is released when the output completes.
+ *	bundirty:
+ *
+ *	Clear B_DELWRI for buffer.
+ *
+ *	Since the buffer is not on a queue, we do not update the numfreebuffers
+ *	count.
+ *	
+ *	Must be called at splbio().
+ *	The buffer must be on QUEUE_NONE.
+ */
+
+void
+bundirty(bp)
+	struct buf *bp;
+{
+	KASSERT(bp->b_qindex == QUEUE_NONE, ("bundirty: buffer %p still on queue %d", bp, bp->b_qindex));
+
+	if (bp->b_flags & B_DELWRI) {
+		bp->b_flags &= ~B_DELWRI;
+		reassignbuf(bp, bp->b_vp);
+		--numdirtybuffers;
+	}
+}
+
+/*
+ *	bawrite:
+ *
+ *	Asynchronous write.  Start output on a buffer, but do not wait for
+ *	it to complete.  The buffer is released when the output completes.
  */
 void
 bawrite(struct buf * bp)
@@ -541,39 +654,42 @@ bawrite(struct buf * bp)
 }
 
 /*
- * Ordered write.
- * Start output on a buffer, and flag it so that the device will write
- * it in the order it was queued.  The buffer is released when the output
- * completes.
+ *	bowrite:
+ *
+ *	Ordered write.  Start output on a buffer, and flag it so that the 
+ *	device will write it in the order it was queued.  The buffer is 
+ *	released when the output completes.
  */
 int
 bowrite(struct buf * bp)
 {
-	bp->b_flags |= B_ORDERED|B_ASYNC;
+	bp->b_flags |= B_ORDERED | B_ASYNC;
 	return (VOP_BWRITE(bp));
 }
 
 /*
- * Release a buffer.
+ *	brelse:
+ *
+ *	Release a busy buffer and, if requested, free its resources.  The
+ *	buffer will be stashed in the appropriate bufqueue[] allowing it
+ *	to be accessed later as a cache entity or reused for other purposes.
  */
 void
 brelse(struct buf * bp)
 {
 	int s;
 
+	KASSERT(!(bp->b_flags & (B_CLUSTER|B_PAGING)), ("brelse: inappropriate B_PAGING or B_CLUSTER bp %p", bp));
+
+#if 0
 	if (bp->b_flags & B_CLUSTER) {
 		relpbuf(bp, NULL);
 		return;
 	}
+#endif
 
 	s = splbio();
 
-	/* anyone need this block? */
-	if (bp->b_flags & B_WANTED) {
-		bp->b_flags &= ~(B_WANTED | B_AGE);
-		wakeup(bp);
-	} 
-
 	if (bp->b_flags & B_LOCKED)
 		bp->b_flags &= ~B_ERROR;
 
@@ -717,8 +833,8 @@ brelse(struct buf * bp)
 	if (bp->b_qindex != QUEUE_NONE)
 		panic("brelse: free buffer onto another queue???");
 #endif
-
 	/* enqueue */
+
 	/* buffers with no memory */
 	if (bp->b_bufsize == 0) {
 		bp->b_flags |= B_INVAL;
@@ -728,7 +844,8 @@ brelse(struct buf * bp)
 		LIST_INSERT_HEAD(&invalhash, bp, b_hash);
 		bp->b_dev = NODEV;
 		kvafreespace += bp->b_kvasize;
-
+		if (bp->b_kvasize)
+			kvaspacewakeup();
 	/* buffers with junk contents */
 	} else if (bp->b_flags & (B_ERROR | B_INVAL | B_NOCACHE | B_RELBUF)) {
 		bp->b_flags |= B_INVAL;
@@ -754,15 +871,38 @@ brelse(struct buf * bp)
 		TAILQ_INSERT_TAIL(&bufqueues[QUEUE_LRU], bp, b_freelist);
 	}
 
-	if ((bp->b_flags & B_INVAL) ||
-		(bp->b_flags & (B_LOCKED|B_DELWRI)) == 0) {
-		if (bp->b_flags & B_DELWRI) {
-			--numdirtybuffers;
-			bp->b_flags &= ~B_DELWRI;
-		}
-		vfs_bio_need_satisfy();
+	/*
+	 * If B_INVAL, clear B_DELWRI.
+	 */
+	if ((bp->b_flags & (B_INVAL|B_DELWRI)) == (B_INVAL|B_DELWRI)) {
+		bp->b_flags &= ~B_DELWRI;
+		--numdirtybuffers;
 	}
 
+	runningbufspace -= bp->b_bufsize;
+
+	/*
+	 * Fixup numfreebuffers count.  The bp is on an appropriate queue
+	 * unless locked.  We then bump numfreebuffers if it is not B_DELWRI.
+	 * We've already handled the B_INVAL case ( B_DELWRI will be clear
+	 * if B_INVAL is set ).
+	 */
+
+	if ((bp->b_flags & B_LOCKED) == 0 && !(bp->b_flags & B_DELWRI))
+		bufcountwakeup();
+
+	/*
+	 * Something we can maybe free.
+	 */
+
+	if (bp->b_bufsize)
+		bufspacewakeup();
+
+	if (bp->b_flags & B_WANTED) {
+		bp->b_flags &= ~(B_WANTED | B_AGE);
+		wakeup(bp);
+	} 
+
 	/* unlock */
 	bp->b_flags &= ~(B_ORDERED | B_WANTED | B_BUSY |
 		B_ASYNC | B_NOCACHE | B_AGE | B_RELBUF);
@@ -770,7 +910,8 @@ brelse(struct buf * bp)
 }
 
 /*
- * Release a buffer.
+ * Release a buffer back to the appropriate queue but do not try to free
+ * it.
  */
 void
 bqrelse(struct buf * bp)
@@ -779,17 +920,12 @@ bqrelse(struct buf * bp)
 
 	s = splbio();
 
-	/* anyone need this block? */
-	if (bp->b_flags & B_WANTED) {
-		bp->b_flags &= ~(B_WANTED | B_AGE);
-		wakeup(bp);
-	} 
+	KASSERT(!(bp->b_flags & (B_CLUSTER|B_PAGING)), ("bqrelse: inappropriate B_PAGING or B_CLUSTER bp %p", bp));
 
 #if !defined(MAX_PERF)
 	if (bp->b_qindex != QUEUE_NONE)
 		panic("bqrelse: free buffer onto another queue???");
 #endif
-
 	if (bp->b_flags & B_LOCKED) {
 		bp->b_flags &= ~B_ERROR;
 		bp->b_qindex = QUEUE_LOCKED;
@@ -800,10 +936,26 @@ bqrelse(struct buf * bp)
 		TAILQ_INSERT_TAIL(&bufqueues[QUEUE_LRU], bp, b_freelist);
 	}
 
-	if ((bp->b_flags & (B_LOCKED|B_DELWRI)) == 0) {
-		vfs_bio_need_satisfy();
+	runningbufspace -= bp->b_bufsize;
+
+	if ((bp->b_flags & B_LOCKED) == 0 &&
+	    ((bp->b_flags & B_INVAL) || !(bp->b_flags & B_DELWRI))
+	) {
+		bufcountwakeup();
 	}
 
+	/*
+	 * Something we can maybe wakeup
+	 */
+	if (bp->b_bufsize)
+		bufspacewakeup();
+
+	/* anyone need this block? */
+	if (bp->b_flags & B_WANTED) {
+		bp->b_flags &= ~(B_WANTED | B_AGE);
+		wakeup(bp);
+	} 
+
 	/* unlock */
 	bp->b_flags &= ~(B_ORDERED | B_WANTED | B_BUSY |
 		B_ASYNC | B_NOCACHE | B_AGE | B_RELBUF);
@@ -847,10 +999,13 @@ vfs_vmio_release(bp)
 			}
 		}
 	}
-	splx(s);
 	bufspace -= bp->b_bufsize;
 	vmiospace -= bp->b_bufsize;
+	runningbufspace -= bp->b_bufsize;
+	splx(s);
 	pmap_qremove(trunc_page((vm_offset_t) bp->b_data), bp->b_npages);
+	if (bp->b_bufsize)
+		bufspacewakeup();
 	bp->b_npages = 0;
 	bp->b_bufsize = 0;
 	bp->b_flags &= ~B_VMIO;
@@ -902,7 +1057,8 @@ vfs_bio_awrite(struct buf * bp)
 
 	s = splbio();
 	/*
-	 * right now we support clustered writing only to regular files
+	 * right now we support clustered writing only to regular files, and
+	 * then only if our I/O system is not saturated.
 	 */
 	if ((vp->v_type == VREG) && 
 	    (vp->v_mount != 0) && /* Only on nodes that have the size info */
@@ -943,279 +1099,358 @@ vfs_bio_awrite(struct buf * bp)
 	 */
 	nwritten = bp->b_bufsize;
 	(void) VOP_BWRITE(bp);
+
 	return nwritten;
 }
 
-
 /*
- * Find a buffer header which is available for use.
+ *	getnewbuf:
+ *
+ *	Find and initialize a new buffer header, freeing up existing buffers 
+ *	in the bufqueues as necessary.
+ *
+ *	We block if:
+ *		We have insufficient buffer headers
+ *		We have insufficient buffer space
+ *		buffer_map is too fragmented ( space reservation fails )
+ *
+ *	We do *not* attempt to flush dirty buffers more then one level deep.
+ *	I.e., if P_FLSINPROG is set we do not flush dirty buffers at all.
+ *
+ *	If P_FLSINPROG is set, we are allowed to dip into our emergency 
+ *	reserve.
  */
 static struct buf *
 getnewbuf(struct vnode *vp, daddr_t blkno,
 	int slpflag, int slptimeo, int size, int maxsize)
 {
-	struct buf *bp, *bp1;
-	int nbyteswritten = 0;
-	vm_offset_t addr;
-	static int writerecursion = 0;
-
-start:
-	if (bufspace >= maxbufspace)
-		goto trytofreespace;
+	struct buf *bp;
+	struct buf *nbp;
+	int outofspace;
+	int nqindex;
+	int defrag = 0;
+	int countawrites = 0;
+	
+restart:
 
-	/* can we constitute a new buffer? */
-	if ((bp = TAILQ_FIRST(&bufqueues[QUEUE_EMPTY]))) {
-#if !defined(MAX_PERF)
-		if (bp->b_qindex != QUEUE_EMPTY)
-			panic("getnewbuf: inconsistent EMPTY queue, qindex=%d",
-			    bp->b_qindex);
-#endif
-		bp->b_flags |= B_BUSY;
-		bremfree(bp);
-		goto fillbuf;
-	}
-trytofreespace:
 	/*
-	 * We keep the file I/O from hogging metadata I/O
-	 * This is desirable because file data is cached in the
-	 * VM/Buffer cache even if a buffer is freed.
+	 * Setup for scan.  If we do not have enough free buffers,
+	 * we setup a degenerate case that falls through the while.
+	 *
+	 * If we are in the middle of a flush, we can dip into the
+	 * emergency reserve.
 	 */
-	if ((bp = TAILQ_FIRST(&bufqueues[QUEUE_AGE]))) {
-#if !defined(MAX_PERF)
-		if (bp->b_qindex != QUEUE_AGE)
-			panic("getnewbuf: inconsistent AGE queue, qindex=%d",
-			    bp->b_qindex);
-#endif
-	} else if ((bp = TAILQ_FIRST(&bufqueues[QUEUE_LRU]))) {
-#if !defined(MAX_PERF)
-		if (bp->b_qindex != QUEUE_LRU)
-			panic("getnewbuf: inconsistent LRU queue, qindex=%d",
-			    bp->b_qindex);
-#endif
-	}
-	if (!bp) {
-		/* wait for a free buffer of any kind */
-		needsbuffer |= VFS_BIO_NEED_ANY;
-		do
-			tsleep(&needsbuffer, (PRIBIO + 4) | slpflag, "newbuf",
-			    slptimeo);
-		while (needsbuffer & VFS_BIO_NEED_ANY);
-		return (0);
+
+	if ((curproc->p_flag & P_FLSINPROG) == 0 &&
+	    numfreebuffers < lofreebuffers
+	) {
+		nqindex = QUEUE_LRU;
+		nbp = NULL;
+	} else {
+		nqindex = QUEUE_EMPTY;
+		if ((nbp = TAILQ_FIRST(&bufqueues[QUEUE_EMPTY])) == NULL) {
+			nqindex = QUEUE_AGE;
+			nbp = TAILQ_FIRST(&bufqueues[QUEUE_AGE]);
+			if (nbp == NULL) {
+				nqindex = QUEUE_LRU;
+				nbp = TAILQ_FIRST(&bufqueues[QUEUE_LRU]);
+			}
+		}
 	}
-	KASSERT(!(bp->b_flags & B_BUSY), 
-	    ("getnewbuf: busy buffer on free list\n"));
+
 	/*
-	 * We are fairly aggressive about freeing VMIO buffers, but since
-	 * the buffering is intact without buffer headers, there is not
-	 * much loss.  We gain by maintaining non-VMIOed metadata in buffers.
+	 * Calculate whether we are out of buffer space.  This state is
+	 * recalculated on every restart.  If we are out of space, we
+	 * have to turn off defragmentation.  The outofspace code will
+	 * defragment too, but the looping conditionals will be messed up
+	 * if both outofspace and defrag are on.
 	 */
-	if ((bp->b_qindex == QUEUE_LRU) && (bp->b_usecount > 0)) {
-		if ((bp->b_flags & B_VMIO) == 0 ||
-			(vmiospace < maxvmiobufspace)) {
-			--bp->b_usecount;
-			TAILQ_REMOVE(&bufqueues[QUEUE_LRU], bp, b_freelist);
-			if (TAILQ_FIRST(&bufqueues[QUEUE_LRU]) != NULL) {
-				TAILQ_INSERT_TAIL(&bufqueues[QUEUE_LRU], bp, b_freelist);
-				goto start;
-			}
-			TAILQ_INSERT_TAIL(&bufqueues[QUEUE_LRU], bp, b_freelist);
+
+	outofspace = 0;
+	if (bufspace >= hibufspace) {
+		if ((curproc->p_flag & P_FLSINPROG) == 0 ||
+		    bufspace >= maxbufspace
+		) {
+			outofspace = 1;
+			defrag = 0;
 		}
 	}
 
+	/*
+	 * defrag state is semi-persistant.  1 means we are flagged for
+	 * defragging.  -1 means we actually defragged something.
+	 */
+	/* nop */
 
-	/* if we are a delayed write, convert to an async write */
-	if ((bp->b_flags & (B_DELWRI | B_INVAL)) == B_DELWRI) {
+	/*
+	 * Run scan, possibly freeing data and/or kva mappings on the fly
+	 * depending.
+	 */
 
+	while ((bp = nbp) != NULL) {
+		int qindex = nqindex;
 		/*
-		 * If our delayed write is likely to be used soon, then
-		 * recycle back onto the LRU queue.
+		 * Calculate next bp ( we can only use it if we do not block
+		 * or do other fancy things ).
 		 */
-		if (vp && (bp->b_vp == vp) && (bp->b_qindex == QUEUE_LRU) &&
-			(bp->b_lblkno >= blkno) && (maxsize > 0)) {
+		if ((nbp = TAILQ_NEXT(bp, b_freelist)) == NULL) {
+			switch(qindex) {
+			case QUEUE_EMPTY:
+				nqindex = QUEUE_AGE;
+				if ((nbp = TAILQ_FIRST(&bufqueues[QUEUE_AGE])))
+					break;
+				/* fall through */
+			case QUEUE_AGE:
+				nqindex = QUEUE_LRU;
+				if ((nbp = TAILQ_FIRST(&bufqueues[QUEUE_LRU])))
+					break;
+				/* fall through */
+			case QUEUE_LRU:
+				/*
+				 * nbp is NULL. 
+				 */
+				break;
+			}
+		}
 
-			if (bp->b_usecount > 0) {
-				if (bp->b_lblkno < blkno + (MAXPHYS / maxsize)) {
+		/*
+		 * Sanity Checks
+		 */
+		KASSERT(!(bp->b_flags & B_BUSY), ("getnewbuf: busy buffer %p on free list", bp));
+		KASSERT(bp->b_qindex == qindex, ("getnewbuf: inconsistant queue %d bp %p", qindex, bp));
 
-					TAILQ_REMOVE(&bufqueues[QUEUE_LRU], bp, b_freelist);
+		/*
+		 * Here we try to move NON VMIO buffers to the end of the 
+		 * LRU queue in order to make VMIO buffers more readily 
+		 * freeable.  We also try to move buffers with a positive
+		 * usecount to the end.
+		 *
+		 * Note that by moving the bp to the end, we setup a following
+		 * loop.  Since we continue to decrement b_usecount this
+		 * is ok and, in fact, desireable.
+		 *
+		 * If we are at the end of the list, we move ourself to the
+		 * same place and need to fixup nbp and nqindex to handle
+		 * the following case.
+		 */
 
-					if (TAILQ_FIRST(&bufqueues[QUEUE_LRU]) != NULL) {
-						TAILQ_INSERT_TAIL(&bufqueues[QUEUE_LRU], bp, b_freelist);
-						bp->b_usecount--;
-						goto start;
-					}
-					TAILQ_INSERT_TAIL(&bufqueues[QUEUE_LRU], bp, b_freelist);
+		if ((qindex == QUEUE_LRU) && bp->b_usecount > 0) {
+			if ((bp->b_flags & B_VMIO) == 0 ||
+			    (vmiospace < maxvmiobufspace)
+			) {
+				--bp->b_usecount;
+				TAILQ_REMOVE(&bufqueues[QUEUE_LRU], bp, b_freelist);
+				TAILQ_INSERT_TAIL(&bufqueues[QUEUE_LRU], bp, b_freelist);
+				if (nbp == NULL) {
+					nqindex = qindex;
+					nbp = bp;
 				}
+				continue;
 			}
 		}
 
 		/*
-		 * Certain layered filesystems can recursively re-enter the vfs_bio
-		 * code, due to delayed writes.  This helps keep the system from
-		 * deadlocking.
+		 * If we come across a delayed write and numdirtybuffers should
+		 * be flushed, try to write it out.  Only if P_FLSINPROG is
+		 * not set.  We can't afford to recursively stack more then
+		 * one deep due to the possibility of having deep VFS call
+		 * stacks.
+		 *
+		 * Limit the number of dirty buffers we are willing to try
+		 * to recover since it really isn't our job here.
 		 */
-		if (writerecursion > 0) {
-			if (writerecursion > 5) {
-				bp = TAILQ_FIRST(&bufqueues[QUEUE_AGE]);
-				while (bp) {
-					if ((bp->b_flags & B_DELWRI) == 0)
-						break;
-					bp = TAILQ_NEXT(bp, b_freelist);
-				}
-				if (bp == NULL) {
-					bp = TAILQ_FIRST(&bufqueues[QUEUE_LRU]);
-					while (bp) {
-						if ((bp->b_flags & B_DELWRI) == 0)
-							break;
-						bp = TAILQ_NEXT(bp, b_freelist);
-					}
-				}
-				if (bp == NULL)
-					panic("getnewbuf: cannot get buffer, infinite recursion failure");
-			} else {
-				bremfree(bp);
-				bp->b_flags |= B_BUSY | B_AGE | B_ASYNC;
-				nbyteswritten += bp->b_bufsize;
-				++writerecursion;
-				VOP_BWRITE(bp);
-				--writerecursion;
-				if (!slpflag && !slptimeo) {
-					return (0);
-				}
-				goto start;
+		if ((bp->b_flags & (B_DELWRI | B_INVAL)) == B_DELWRI) {
+			if ((curproc->p_flag & P_FLSINPROG) || 
+			    numdirtybuffers < hidirtybuffers ||
+			    countawrites > 16
+			) {
+				continue;
 			}
-		} else {
-			++writerecursion;
-			nbyteswritten += vfs_bio_awrite(bp);
-			--writerecursion;
-			if (!slpflag && !slptimeo) {
-				return (0);
+			curproc->p_flag |= P_FLSINPROG;
+			vfs_bio_awrite(bp);
+			curproc->p_flag &= ~P_FLSINPROG;
+			++countawrites;
+			goto restart;
+		}
+
+		if (defrag > 0 && bp->b_kvasize == 0)
+			continue;
+		if (outofspace > 0 && bp->b_bufsize == 0)
+			continue;
+
+		/*
+		 * Start freeing the bp.  This is somewhat involved.  nbp
+		 * remains valid only for QUEUE_EMPTY bp's.
+		 */
+
+		bremfree(bp);
+		bp->b_flags |= B_BUSY;
+
+		if (qindex == QUEUE_LRU || qindex == QUEUE_AGE) {
+			if (bp->b_flags & B_VMIO) {
+				bp->b_flags &= ~B_ASYNC;
+				vfs_vmio_release(bp);
 			}
-			goto start;
+			if (bp->b_vp)
+				brelvp(bp);
 		}
-	}
 
-	if (bp->b_flags & B_WANTED) {
-		bp->b_flags &= ~B_WANTED;
-		wakeup(bp);
-	}
-	bremfree(bp);
-	bp->b_flags |= B_BUSY;
+		if (bp->b_flags & B_WANTED) {
+			bp->b_flags &= ~B_WANTED;
+			wakeup(bp);
+		}
 
-	if (bp->b_flags & B_VMIO) {
-		bp->b_flags &= ~B_ASYNC;
-		vfs_vmio_release(bp);
-	}
+		/*
+		 * NOTE:  nbp is now entirely invalid.  We can only restart
+		 * the scan from this point on.
+		 *
+		 * Get the rest of the buffer freed up.  b_kva* is still
+		 * valid after this operation.
+		 */
 
-	if (bp->b_vp)
-		brelvp(bp);
+		if (bp->b_rcred != NOCRED) {
+			crfree(bp->b_rcred);
+			bp->b_rcred = NOCRED;
+		}
+		if (bp->b_wcred != NOCRED) {
+			crfree(bp->b_wcred);
+			bp->b_wcred = NOCRED;
+		}
+		if (LIST_FIRST(&bp->b_dep) != NULL && bioops.io_deallocate)
+			(*bioops.io_deallocate)(bp);
 
-fillbuf:
+		LIST_REMOVE(bp, b_hash);
+		LIST_INSERT_HEAD(&invalhash, bp, b_hash);
 
-	/* we are not free, nor do we contain interesting data */
-	if (bp->b_rcred != NOCRED) {
-		crfree(bp->b_rcred);
-		bp->b_rcred = NOCRED;
-	}
-	if (bp->b_wcred != NOCRED) {
-		crfree(bp->b_wcred);
-		bp->b_wcred = NOCRED;
-	}
-	if (LIST_FIRST(&bp->b_dep) != NULL &&
-	    bioops.io_deallocate)
-		(*bioops.io_deallocate)(bp);
-
-	LIST_REMOVE(bp, b_hash);
-	LIST_INSERT_HEAD(&invalhash, bp, b_hash);
-	if (bp->b_bufsize) {
-		allocbuf(bp, 0);
-	}
-	bp->b_flags = B_BUSY;
-	bp->b_dev = NODEV;
-	bp->b_vp = NULL;
-	bp->b_blkno = bp->b_lblkno = 0;
-	bp->b_offset = NOOFFSET;
-	bp->b_iodone = 0;
-	bp->b_error = 0;
-	bp->b_resid = 0;
-	bp->b_bcount = 0;
-	bp->b_npages = 0;
-	bp->b_dirtyoff = bp->b_dirtyend = 0;
-	bp->b_validoff = bp->b_validend = 0;
-	bp->b_usecount = 5;
-	/* Here, not kern_physio.c, is where this should be done*/
-	LIST_INIT(&bp->b_dep);
+		if (bp->b_bufsize)
+			allocbuf(bp, 0);
 
-	maxsize = (maxsize + PAGE_MASK) & ~PAGE_MASK;
+		bp->b_flags = B_BUSY;
+		bp->b_dev = NODEV;
+		bp->b_vp = NULL;
+		bp->b_blkno = bp->b_lblkno = 0;
+		bp->b_offset = NOOFFSET;
+		bp->b_iodone = 0;
+		bp->b_error = 0;
+		bp->b_resid = 0;
+		bp->b_bcount = 0;
+		bp->b_npages = 0;
+		bp->b_dirtyoff = bp->b_dirtyend = 0;
+		bp->b_validoff = bp->b_validend = 0;
+		bp->b_usecount = 5;
+
+		LIST_INIT(&bp->b_dep);
 
-	/*
-	 * we assume that buffer_map is not at address 0
-	 */
-	addr = 0;
-	if (maxsize != bp->b_kvasize) {
-		bfreekva(bp);
-		
-findkvaspace:
 		/*
-		 * See if we have buffer kva space
+		 * Ok, now that we have a free buffer, if we are defragging
+		 * we have to recover the kvaspace.
 		 */
-		if (vm_map_findspace(buffer_map,
-			vm_map_min(buffer_map), maxsize, &addr)) {
-			if (kvafreespace > 0) {
-				int totfree = 0, freed;
-				do {
-					freed = 0;
-					for (bp1 = TAILQ_FIRST(&bufqueues[QUEUE_EMPTY]);
-						bp1 != NULL; bp1 = TAILQ_NEXT(bp1, b_freelist)) {
-						if (bp1->b_kvasize != 0) {
-							totfree += bp1->b_kvasize;
-							freed = bp1->b_kvasize;
-							bremfree(bp1);
-							bfreekva(bp1);
-							brelse(bp1);
-							break;
-						}
-					}
-				} while (freed);
-				/*
-				 * if we found free space, then retry with the same buffer.
-				 */
-				if (totfree)
-					goto findkvaspace;
-			}
+
+		if (defrag > 0) {
+			defrag = -1;
 			bp->b_flags |= B_INVAL;
+			bfreekva(bp);
 			brelse(bp);
-			goto trytofreespace;
+			goto restart;
 		}
-	}
 
-	/*
-	 * See if we are below are allocated minimum
-	 */
-	if (bufspace >= (maxbufspace + nbyteswritten)) {
-		bp->b_flags |= B_INVAL;
-		brelse(bp);
-		goto trytofreespace;
+		if (outofspace > 0) {
+			outofspace = -1;
+			bp->b_flags |= B_INVAL;
+			bfreekva(bp);
+			brelse(bp);
+			goto restart;
+		}
+
+		/*
+		 * We are done
+		 */
+		break;
 	}
 
 	/*
-	 * create a map entry for the buffer -- in essence
-	 * reserving the kva space.
+	 * If we exhausted our list, sleep as appropriate.
 	 */
-	if (addr) {
-		vm_map_insert(buffer_map, NULL, 0,
-			addr, addr + maxsize,
-			VM_PROT_ALL, VM_PROT_ALL, MAP_NOFAULT);
 
-		bp->b_kvabase = (caddr_t) addr;
-		bp->b_kvasize = maxsize;
+	if (bp == NULL) {
+		int flags;
+
+dosleep:
+		if (defrag > 0)
+			flags = VFS_BIO_NEED_KVASPACE;
+		else if (outofspace > 0)
+			flags = VFS_BIO_NEED_BUFSPACE;
+		else
+			flags = VFS_BIO_NEED_ANY;
+
+		if (rushjob < syncdelay / 2)
+			++rushjob;
+		needsbuffer |= flags;
+		while (needsbuffer & flags) {
+			tsleep(
+			    &needsbuffer, 
+			    (PRIBIO + 4) | slpflag, 
+			    "newbuf",
+			    slptimeo
+			);
+		}
+	} else {
+		/*
+		 * We finally have a valid bp.  We aren't quite out of the
+		 * woods, we still have to reserve kva space.
+		 */
+		vm_offset_t addr = 0;
+
+		maxsize = (maxsize + PAGE_MASK) & ~PAGE_MASK;
+
+		if (maxsize != bp->b_kvasize) {
+			bfreekva(bp);
+
+			if (vm_map_findspace(buffer_map,
+				vm_map_min(buffer_map), maxsize, &addr)
+			) {
+				/*
+				 * Uh oh.  Buffer map is to fragmented.  Try
+				 * to defragment.
+				 */
+				if (defrag <= 0) {
+					defrag = 1;
+					bp->b_flags |= B_INVAL;
+					brelse(bp);
+					goto restart;
+				}
+				/*
+				 * Uh oh.  We couldn't seem to defragment
+				 */
+				bp = NULL;
+				goto dosleep;
+			}
+		}
+		if (addr) {
+			vm_map_insert(buffer_map, NULL, 0,
+				addr, addr + maxsize,
+				VM_PROT_ALL, VM_PROT_ALL, MAP_NOFAULT);
+
+			bp->b_kvabase = (caddr_t) addr;
+			bp->b_kvasize = maxsize;
+			bp->b_data = bp->b_kvabase;
+		}
 	}
-	bp->b_data = bp->b_kvabase;
 	
 	return (bp);
 }
 
+/*
+ *	waitfreebuffers:
+ *
+ *	Wait for sufficient free buffers.  This routine is not called if
+ *	curproc is the update process so we do not have to do anything 
+ *	fancy.
+ */
+
 static void
-waitfreebuffers(int slpflag, int slptimeo) {
+waitfreebuffers(int slpflag, int slptimeo) 
+{
 	while (numfreebuffers < hifreebuffers) {
 		flushdirtybuffers(slpflag, slptimeo);
 		if (numfreebuffers < hifreebuffers)
@@ -1226,48 +1461,80 @@ waitfreebuffers(int slpflag, int slptimeo) {
 	}
 }
 
+/*
+ *	flushdirtybuffers:
+ *
+ *	This routine is called when we get too many dirty buffers.  
+ *
+ *	We have to protect ourselves from recursion, but we also do not want
+ *	other process's flushdirtybuffers() to interfere with the syncer if
+ *	it decides to flushdirtybuffers().
+ *
+ *	In order to maximize operations, we allow any process to flush
+ *	dirty buffers and use P_FLSINPROG to prevent recursion.  
+ */
+
 static void
-flushdirtybuffers(int slpflag, int slptimeo) {
+flushdirtybuffers(int slpflag, int slptimeo) 
+{
 	int s;
-	static pid_t flushing = 0;
 
 	s = splbio();
 
-	if (flushing) {
-		if (flushing == curproc->p_pid) {
-			splx(s);
-			return;
-		}
-		while (flushing) {
-			if (tsleep(&flushing, (PRIBIO + 4)|slpflag, "biofls", slptimeo)) {
-				splx(s);
-				return;
-			}
-		}
+	if (curproc->p_flag & P_FLSINPROG) {
+		splx(s);
+		return;
 	}
-	flushing = curproc->p_pid;
+	curproc->p_flag |= P_FLSINPROG;
 
 	while (numdirtybuffers > lodirtybuffers) {
-		struct buf *bp;
-		needsbuffer |= VFS_BIO_NEED_LOWLIMIT;
-		bp = TAILQ_FIRST(&bufqueues[QUEUE_AGE]);
-		if (bp == NULL)
-			bp = TAILQ_FIRST(&bufqueues[QUEUE_LRU]);
-
-		while (bp && ((bp->b_flags & B_DELWRI) == 0)) {
-			bp = TAILQ_NEXT(bp, b_freelist);
+		if (flushbufqueues() == 0)
+			break;
+	}
+
+	curproc->p_flag &= ~P_FLSINPROG;
+
+	splx(s);
+}
+
+static int
+flushbufqueues(void)
+{
+	struct buf *bp;
+	int qindex;
+	int r = 0;
+
+	qindex = QUEUE_AGE;
+	bp = TAILQ_FIRST(&bufqueues[QUEUE_AGE]);
+
+	for (;;) {
+		if (bp == NULL) {
+			if (qindex == QUEUE_LRU)
+				break;
+			qindex = QUEUE_LRU;
+			if ((bp = TAILQ_FIRST(&bufqueues[QUEUE_LRU])) == NULL)
+				break;
 		}
 
-		if (bp) {
-			vfs_bio_awrite(bp);
-			continue;
+		/*
+		 * XXX NFS does weird things with B_INVAL bps if we bwrite
+		 * them ( vfs_bio_awrite/bawrite/bdwrite/etc )  Why?
+		 *
+		 */
+		if ((bp->b_flags & B_DELWRI) != 0) {
+			if (bp->b_flags & B_INVAL) {
+				bremfree(bp);
+				bp->b_flags |= B_BUSY;
+				brelse(bp);
+			} else {
+				vfs_bio_awrite(bp);
+			}
+			++r;
+			break;
 		}
-		break;
+		bp = TAILQ_NEXT(bp, b_freelist);
 	}
-
-	flushing = 0;
-	wakeup(&flushing);
-	splx(s);
+	return(r);
 }
 
 /*
@@ -1335,21 +1602,29 @@ inmem(struct vnode * vp, daddr_t blkno)
  * code, and used by the nfs read code.
  */
 static void
-vfs_setdirty(struct buf *bp) {
+vfs_setdirty(struct buf *bp) 
+{
 	int i;
 	vm_object_t object;
 	vm_offset_t boffset;
-#if 0
-	vm_offset_t offset;
-#endif
 
 	/*
 	 * We qualify the scan for modified pages on whether the
 	 * object has been flushed yet.  The OBJ_WRITEABLE flag
 	 * is not cleared simply by protecting pages off.
 	 */
-	if ((bp->b_flags & B_VMIO) &&
-		((object = bp->b_pages[0]->object)->flags & (OBJ_WRITEABLE|OBJ_CLEANING))) {
+
+	if ((bp->b_flags & B_VMIO) == 0)
+		return;
+
+	object = bp->b_pages[0]->object;
+
+	if ((object->flags & OBJ_WRITEABLE) && !(object->flags & OBJ_MIGHTBEDIRTY))
+		printf("Warning: object %p writeable but not mightbedirty\n", object);
+	if (!(object->flags & OBJ_WRITEABLE) && (object->flags & OBJ_MIGHTBEDIRTY))
+		printf("Warning: object %p mightbedirty but not writeable\n", object);
+
+	if (object->flags & (OBJ_MIGHTBEDIRTY|OBJ_CLEANING)) {
 		/*
 		 * test the pages to see if they have been modified directly
 		 * by users through the VM system.
@@ -1410,7 +1685,15 @@ getblk(struct vnode * vp, daddr_t blkno, int size, int slpflag, int slptimeo)
 
 	s = splbio();
 loop:
-	if (numfreebuffers < lofreebuffers) {
+	/*
+	 * Block if we are low on buffers.  The syncer is allowed more
+	 * buffers in order to avoid a deadlock.
+	 */
+	if (curproc == updateproc && numfreebuffers == 0) {
+		needsbuffer |= VFS_BIO_NEED_ANY;
+		tsleep(&needsbuffer, (PRIBIO + 4) | slpflag, "newbuf",
+		    slptimeo);
+	} else if (curproc != updateproc && numfreebuffers < lofreebuffers) {
 		waitfreebuffers(slpflag, slptimeo);
 	}
 
@@ -1655,6 +1938,9 @@ allocbuf(struct buf *bp, int size)
 					free(bp->b_data, M_BIOBUF);
 					bufspace -= bp->b_bufsize;
 					bufmallocspace -= bp->b_bufsize;
+					runningbufspace -= bp->b_bufsize;
+					if (bp->b_bufsize)
+						bufspacewakeup();
 					bp->b_data = bp->b_kvabase;
 					bp->b_bufsize = 0;
 					bp->b_bcount = 0;
@@ -1683,6 +1969,7 @@ allocbuf(struct buf *bp, int size)
 				bp->b_flags |= B_MALLOC;
 				bufspace += mbsize;
 				bufmallocspace += mbsize;
+				runningbufspace += bp->b_bufsize;
 				return 1;
 			}
 #endif
@@ -1699,6 +1986,9 @@ allocbuf(struct buf *bp, int size)
 				bp->b_data = bp->b_kvabase;
 				bufspace -= bp->b_bufsize;
 				bufmallocspace -= bp->b_bufsize;
+				runningbufspace -= bp->b_bufsize;
+				if (bp->b_bufsize)
+					bufspacewakeup();
 				bp->b_bufsize = 0;
 				bp->b_flags &= ~B_MALLOC;
 				newbsize = round_page(newbsize);
@@ -1862,6 +2152,9 @@ allocbuf(struct buf *bp, int size)
 	if (bp->b_flags & B_VMIO)
 		vmiospace += (newbsize - bp->b_bufsize);
 	bufspace += (newbsize - bp->b_bufsize);
+	runningbufspace += (newbsize - bp->b_bufsize);
+	if (newbsize < bp->b_bufsize)
+		bufspacewakeup();
 	bp->b_bufsize = newbsize;
 	bp->b_bcount = size;
 	return 1;
@@ -1909,18 +2202,9 @@ biodone(register struct buf * bp)
 
 	s = splbio();
 
-#if !defined(MAX_PERF)
-	if (!(bp->b_flags & B_BUSY))
-		panic("biodone: buffer not busy");
-#endif
+	KASSERT((bp->b_flags & B_BUSY), ("biodone: bp %p not busy", bp));
+	KASSERT(!(bp->b_flags & B_DONE), ("biodone: bp %p already done", bp));
 
-	if (bp->b_flags & B_DONE) {
-		splx(s);
-#if !defined(MAX_PERF)
-		printf("biodone: buffer already done\n");
-#endif
-		return;
-	}
 	bp->b_flags |= B_DONE;
 
 	if (bp->b_flags & B_FREEBUF) {