Index: sys/vm/swap_pager.c
===================================================================
--- sys/vm/swap_pager.c
+++ sys/vm/swap_pager.c
@@ -424,7 +424,8 @@
 static void swp_pager_meta_transfer(vm_object_t src, vm_object_t dst,
     vm_pindex_t pindex, vm_pindex_t count);
 static void swp_pager_meta_free_all(vm_object_t);
-static daddr_t swp_pager_meta_lookup(vm_object_t, vm_pindex_t);
+static daddr_t swp_pager_meta_lookup(vm_object_t object, vm_pindex_t pindex0,
+    int *before, int *after);
 
 static void
 swp_pager_init_freerange(daddr_t *start, daddr_t *num)
@@ -943,7 +944,8 @@
 	KASSERT(srcobject->type == OBJT_SWAP,
 	    ("%s: Srcobject not swappable", __func__));
 	if (dstobject->type == OBJT_SWAP &&
-	    swp_pager_meta_lookup(dstobject, pindex) != SWAPBLK_NONE) {
+	    swp_pager_meta_lookup(dstobject, pindex, NULL, NULL) !=
+	    SWAPBLK_NONE) {
 		/* Caller should destroy the source block. */
 		return (false);
 	}
@@ -1047,17 +1049,18 @@
 swap_pager_haspage(vm_object_t object, vm_pindex_t pindex, int *before,
     int *after)
 {
-	daddr_t blk, blk0;
-	int i;
+	daddr_t blk0;
 
+	if (before)
+		*before = SWB_NPAGES - 1;
+	if (after)
+		*after = SWB_NPAGES - 1;
+
 	VM_OBJECT_ASSERT_LOCKED(object);
 	KASSERT(object->type == OBJT_SWAP,
 	    ("%s: object not swappable", __func__));
 
-	/*
-	 * do we have good backing store at the requested index ?
-	 */
-	blk0 = swp_pager_meta_lookup(object, pindex);
+	blk0 = swp_pager_meta_lookup(object, pindex, before, after);
 	if (blk0 == SWAPBLK_NONE) {
 		if (before)
 			*before = 0;
@@ -1066,31 +1069,6 @@
 		return (FALSE);
 	}
 
-	/*
-	 * find backwards-looking contiguous good backing store
-	 */
-	if (before != NULL) {
-		for (i = 1; i < SWB_NPAGES; i++) {
-			if (i > pindex)
-				break;
-			blk = swp_pager_meta_lookup(object, pindex - i);
-			if (blk != blk0 - i)
-				break;
-		}
-		*before = i - 1;
-	}
-
-	/*
-	 * find forward-looking contiguous good backing store
-	 */
-	if (after != NULL) {
-		for (i = 1; i < SWB_NPAGES; i++) {
-			blk = swp_pager_meta_lookup(object, pindex + i);
-			if (blk != blk0 + i)
-				break;
-		}
-		*after = i - 1;
-	}
 	return (TRUE);
 }
 
@@ -1231,7 +1209,7 @@
 	vm_object_pip_add(object, count);
 
 	pindex = bm->pindex;
-	blk = swp_pager_meta_lookup(object, pindex);
+	blk = swp_pager_meta_lookup(object, pindex, NULL, NULL);
 	KASSERT(blk != SWAPBLK_NONE,
 	    ("no swap blocking containing %p(%jx)", object, (uintmax_t)pindex));
 
@@ -2138,23 +2116,34 @@
 }
 
 /*
- * SWP_PAGER_METACTL() -  misc control of swap meta data.
+ * SWP_PAGER_META_LOOKUP() -	lookup good backing store for
+ *	the requested page and optionally the number of continuous blocks.
  *
- *	This routine is capable of looking up, or removing swapblk
- *	assignments in the swap meta data.  It returns the swapblk being
- *	looked-up, popped, or SWAPBLK_NONE if the block was invalid.
+ *	This routine looks up swapblk assignment in the swap meta data.
+ *      In addition, if before and/or after are provided with a limit value,
+ *	it looks for the number of continuous blocks backward and forward.
  *
- *	When acting on a busy resident page and paging is in progress, we
- *	have to wait until paging is complete but otherwise can act on the
- *	busy page.
+ *	This returns SWAPBLK_NONE if swblk at pindex isn't associated to
+ *      swap meta data; *before and *after are not modified for this case.
+ *	Otherwise, return the swap address of pindex.  If *before and/or
+ *      *after are provided with positive numbers, the number of continuous
+ *	blocks before and/or after up to provided limits are searched and
+ *	returned.
+ *
+ *      Input - "object" and "pindex0"
+ *      Input/Output - "before" and "after" - the number of continuous blocks
+ *		to look for as input and its actual size as output.
  */
 static daddr_t
-swp_pager_meta_lookup(vm_object_t object, vm_pindex_t pindex)
+swp_pager_meta_lookup(vm_object_t object, vm_pindex_t pindex0, int *before,
+    int *after)
 {
-	struct swblk *sb;
+	struct swblk *sb, *sbb;
+	vm_pindex_t pindex, pindexb;
+	daddr_t r0;
+	int i, i0, end, offset;
 
 	VM_OBJECT_ASSERT_LOCKED(object);
-
 	/*
 	 * The meta data only exists if the object is OBJT_SWAP
 	 * and even then might not be allocated yet.
@@ -2162,11 +2151,72 @@
 	KASSERT(object->type == OBJT_SWAP,
 	    ("Lookup object not swappable"));
 
-	sb = SWAP_PCTRIE_LOOKUP(&object->un_pager.swp.swp_blks,
-	    rounddown(pindex, SWAP_META_PAGES));
-	if (sb == NULL)
+	i0 = pindex0 % SWAP_META_PAGES;
+	pindex = rounddown(pindex0, SWAP_META_PAGES);
+
+	sb = SWAP_PCTRIE_LOOKUP(&object->un_pager.swp.swp_blks, pindex);
+	if (sb == NULL || sb->d[i0] == SWAPBLK_NONE)
 		return (SWAPBLK_NONE);
-	return (sb->d[pindex % SWAP_META_PAGES]);
+	r0 = sb->d[i0];
+
+	if (before) {
+		if (*before <= 0 || pindex0 == 0) {
+			*before = 0;
+			goto finished_backward;
+		}
+		offset = 1;
+		pindexb = pindex;
+		sbb = sb;
+		if (pindex0 < *before) /* some pindexes are less than 0. */
+			end = pindex0;
+		else
+			end = *before;
+		i = i0 - 1;
+		do {
+			for (; i >= 0; --i, ++offset) {
+				if (r0 - offset != sbb->d[i]) {
+					*before = offset - 1;
+					goto finished_backward;
+				}
+				if (offset == end) {
+					*before = offset;
+					goto finished_backward;
+				}
+			}
+			pindexb -= SWAP_META_PAGES;
+			i = SWAP_META_PAGES - 1;
+		} while ((sbb = SWAP_PCTRIE_LOOKUP(
+		    &object->un_pager.swp.swp_blks, pindexb)) != NULL);
+		*before = offset - 1;
+	}
+finished_backward:
+	if (!after)
+		return (r0);
+	if (*after <= 0) {
+		*after = 0;
+		return (r0);
+	}
+
+	offset = 1;
+	end = *after; /* how do I check overflow? */
+	i = i0 + 1;
+	do {
+		for (; i < SWAP_META_PAGES; ++i, ++offset) {
+			if (r0 + offset != sb->d[i]) {
+				*after = offset - 1;
+				return (r0);
+			}
+			if (offset == end) {
+				*after = offset;
+				return (r0);
+			}
+		}
+		pindex += SWAP_META_PAGES;
+		i = 0;
+	} while ((sb = SWAP_PCTRIE_LOOKUP(&object->un_pager.swp.swp_blks,
+	    pindex)) != NULL);
+	*after = offset - 1;
+	return (r0);
 }
 
 /*