diff --git a/sys/kern/vfs_bio.c b/sys/kern/vfs_bio.c
index 10ee88328875..d6392c025a94 100644
--- a/sys/kern/vfs_bio.c
+++ b/sys/kern/vfs_bio.c
@@ -206,7 +206,7 @@ static int sysctl_bufspace(SYSCTL_HANDLER_ARGS);
 int vmiodirenable = TRUE;
 SYSCTL_INT(_vfs, OID_AUTO, vmiodirenable, CTLFLAG_RW, &vmiodirenable, 0,
     "Use the VM system for directory writes");
-long runningbufspace;
+static long runningbufspace;
 SYSCTL_LONG(_vfs, OID_AUTO, runningbufspace, CTLFLAG_RD, &runningbufspace, 0,
     "Amount of presently outstanding async buffer io");
 SYSCTL_PROC(_vfs, OID_AUTO, bufspace, CTLTYPE_LONG|CTLFLAG_MPSAFE|CTLFLAG_RD,
@@ -941,6 +941,16 @@ runningbufwakeup(struct buf *bp)
 	runningwakeup();
 }
 
+long
+runningbufclaim(struct buf *bp, int space)
+{
+	long old;
+
+	old = atomic_fetchadd_long(&runningbufspace, space);
+	bp->b_runningbufspace = space;
+	return (old);
+}
+
 /*
  *	waitrunningbufspace()
  *
@@ -2352,8 +2362,7 @@ bufwrite(struct buf *bp)
 	/*
 	 * Normal bwrites pipeline writes
 	 */
-	bp->b_runningbufspace = bp->b_bufsize;
-	space = atomic_fetchadd_long(&runningbufspace, bp->b_runningbufspace);
+	space = runningbufclaim(bp, bp->b_bufsize);
 
 #ifdef RACCT
 	if (racct_enable) {
diff --git a/sys/sys/buf.h b/sys/sys/buf.h
index 832cfaa617a5..9d916faef4b1 100644
--- a/sys/sys/buf.h
+++ b/sys/sys/buf.h
@@ -519,7 +519,6 @@ extern int	nbuf;			/* The number of buffer headers */
 extern u_long	maxswzone;		/* Max KVA for swap structures */
 extern u_long	maxbcache;		/* Max KVA for buffer cache */
 extern int	maxbcachebuf;		/* Max buffer cache block size */
-extern long	runningbufspace;
 extern long	hibufspace;
 extern int	dirtybufthresh;
 extern int	bdwriteskip;
@@ -536,6 +535,7 @@ buf_mapped(struct buf *bp)
 	return (bp->b_data != unmapped_buf);
 }
 
+long	runningbufclaim(struct buf *, int);
 void	runningbufwakeup(struct buf *);
 void	waitrunningbufspace(void);
 caddr_t	kern_vfs_bio_buffer_alloc(caddr_t v, long physmem_est);
diff --git a/sys/ufs/ffs/ffs_snapshot.c b/sys/ufs/ffs/ffs_snapshot.c
index b0adb6c033c7..f4eed782f7bc 100644
--- a/sys/ufs/ffs/ffs_snapshot.c
+++ b/sys/ufs/ffs/ffs_snapshot.c
@@ -2343,9 +2343,8 @@ ffs_copyonwrite(struct vnode *devvp, struct buf *bp)
 		    TAILQ_EMPTY(&sn->sn_head)) {
 			VI_UNLOCK(devvp);
 			if (saved_runningbufspace != 0) {
-				bp->b_runningbufspace = saved_runningbufspace;
-				atomic_add_long(&runningbufspace,
-					       bp->b_runningbufspace);
+				(void)runningbufclaim(bp,
+				    saved_runningbufspace);
 			}
 			return (0);		/* Snapshot gone */
 		}
@@ -2479,10 +2478,8 @@ ffs_copyonwrite(struct vnode *devvp, struct buf *bp)
 	/*
 	 * I/O on bp will now be started, so count it in runningbufspace.
 	 */
-	if (saved_runningbufspace != 0) {
-		bp->b_runningbufspace = saved_runningbufspace;
-		atomic_add_long(&runningbufspace, bp->b_runningbufspace);
-	}
+	if (saved_runningbufspace != 0)
+		(void)runningbufclaim(bp, saved_runningbufspace);
 	return (error);
 }
 
diff --git a/sys/ufs/ffs/ffs_vfsops.c b/sys/ufs/ffs/ffs_vfsops.c
index bcf7f0f05a7b..2bfee6a6145d 100644
--- a/sys/ufs/ffs/ffs_vfsops.c
+++ b/sys/ufs/ffs/ffs_vfsops.c
@@ -2517,9 +2517,7 @@ ffs_geom_strategy(struct bufobj *bo, struct buf *bp)
 						return;
 					}
 				}
-				bp->b_runningbufspace = bp->b_bufsize;
-				atomic_add_long(&runningbufspace,
-					       bp->b_runningbufspace);
+				(void)runningbufclaim(bp, bp->b_bufsize);
 			} else {
 				error = ffs_copyonwrite(vp, bp);
 				if (error != 0 && error != EOPNOTSUPP) {
diff --git a/sys/vm/vnode_pager.c b/sys/vm/vnode_pager.c
index 98b905f27c4a..842d4ab89b90 100644
--- a/sys/vm/vnode_pager.c
+++ b/sys/vm/vnode_pager.c
@@ -717,8 +717,7 @@ vnode_pager_input_smlfs(vm_object_t object, vm_page_t m)
 			bp->b_vp = vp;
 			bp->b_bcount = bsize;
 			bp->b_bufsize = bsize;
-			bp->b_runningbufspace = bp->b_bufsize;
-			atomic_add_long(&runningbufspace, bp->b_runningbufspace);
+			(void)runningbufclaim(bp, bp->b_bufsize);
 
 			/* do the input */
 			bp->b_iooffset = dbtob(bp->b_blkno);
@@ -1160,7 +1159,7 @@ vnode_pager_generic_getpages(struct vnode *vp, vm_page_t *m, int count,
 	bp->b_wcred = crhold(curthread->td_ucred);
 	pbgetbo(bo, bp);
 	bp->b_vp = vp;
-	bp->b_bcount = bp->b_bufsize = bp->b_runningbufspace = bytecount;
+	bp->b_bcount = bp->b_bufsize = bytecount;
 	bp->b_iooffset = dbtob(bp->b_blkno);
 	KASSERT(IDX_TO_OFF(m[0]->pindex - bp->b_pages[0]->pindex) ==
 	    (blkno0 - bp->b_blkno) * DEV_BSIZE +
@@ -1170,7 +1169,8 @@ vnode_pager_generic_getpages(struct vnode *vp, vm_page_t *m, int count,
 	    (uintmax_t)m[0]->pindex, (uintmax_t)bp->b_pages[0]->pindex,
 	    (uintmax_t)blkno0, (uintmax_t)bp->b_blkno));
 
-	atomic_add_long(&runningbufspace, bp->b_runningbufspace);
+	(void)runningbufclaim(bp, bp->b_bufsize);
+
 	VM_CNT_INC(v_vnodein);
 	VM_CNT_ADD(v_vnodepgsin, bp->b_npages);