--- kernel/bsd/vfs/vfs_bio.c	2018/04/24 18:26:06	1.1.1.1
+++ kernel/bsd/vfs/vfs_bio.c	2018/04/24 18:31:23	1.1.1.2
@@ -151,8 +151,25 @@ int needbuffer;
 /*
  * Insq/Remq for the buffer free lists.
  */
-#define	binsheadfree(bp, dp)	TAILQ_INSERT_HEAD(dp, bp, b_freelist)
-#define	binstailfree(bp, dp)	TAILQ_INSERT_TAIL(dp, bp, b_freelist)
+#define	binsheadfree(bp, dp)	do { \
+				    TAILQ_INSERT_HEAD(dp, bp, b_freelist); \
+				    (bp)->b_timestamp = time.tv_sec; \
+				} while (0)
+
+#define	binstailfree(bp, dp)	do { \
+				    TAILQ_INSERT_TAIL(dp, bp, b_freelist); \
+				    (bp)->b_timestamp = time.tv_sec; \
+				} while (0)
+
+
+/* Time in seconds before a buf on a list is considered as a stale buf */
+#define LRU_IS_STALE 120 /* default value for the LRU */
+#define AGE_IS_STALE 60  /* default value for the AGE */
+
+int lru_is_stale = LRU_IS_STALE;
+int age_is_stale = AGE_IS_STALE;
+
+
 
 void
 bremfree(bp)
@@ -175,6 +192,7 @@ bremfree(bp)
 			panic("bremfree: lost tail");
 	}
 	TAILQ_REMOVE(dp, bp, b_freelist);
+	bp->b_timestamp = 0; 
 }
 
 /*
@@ -736,21 +754,46 @@ getnewbuf(slpflag, slptimeo)
 	int slpflag, slptimeo;
 {
 	register struct buf *bp;
+	register struct buf *lru_bp;
+	register struct buf *age_bp;
+	register int age_time, lru_time;
 	int s;
 	struct ucred *cred;
 
 start:
 	s = splbio();
-	if ((bp = bufqueues[BQ_AGE].tqh_first) != NULL ||
-	    (bp = bufqueues[BQ_LRU].tqh_first) != NULL) {
-		bremfree(bp);
-	} else {
+
+	age_bp = bufqueues[BQ_AGE].tqh_first;
+	lru_bp = bufqueues[BQ_LRU].tqh_first;
+
+	if (age_bp == NULL && lru_bp == NULL) {
 		/* wait for a free buffer of any kind */
 		needbuffer = 1;
 		tsleep(&needbuffer, slpflag|(PRIBIO+1), "getnewbuf", slptimeo);
 		splx(s);
 		return (0);
 	}
+	if (age_bp == NULL)
+		bp = lru_bp;
+	else if (lru_bp == NULL)
+		bp = age_bp;
+	else {
+		if (((age_time = (time.tv_sec - age_bp->b_timestamp)) < 0) ||
+			((lru_time = (time.tv_sec - lru_bp->b_timestamp)) < 0)) {
+			/* time was set backwards */
+			bp = age_bp;
+			/*
+			 * we should probably re-timestamp eveything in the queues
+			 * at this point with the current time
+			 */
+		} else {
+			if (lru_time >= lru_is_stale && age_time < age_is_stale)
+				bp = lru_bp;
+			else
+				bp = age_bp;
+		}
+	}
+	bremfree(bp);
 
 	/* Buffer is no longer on free lists. */
 	SET(bp->b_flags, B_BUSY);
@@ -973,6 +1016,7 @@ alloc_io_buf(vp)
 		return (NULL);
 	}
 	TAILQ_REMOVE(&iobufqueue, bp, b_freelist);
+	bp->b_timestamp = 0; 
 
 	/* clear out various fields */
 	bp->b_flags = (B_BUSY | B_RAW);