When the function blist_fill() was added to the kernel in r107913, the swap

pager used a different scheme for striping the allocation of swap space
across multiple devices.  And, although blist_fill() was intended to support
fill operations with large counts, the old striping scheme never performed a
fill larger than the stripe size.  Consequently, the misplacement of a
sanity check in blst_meta_fill() went undetected.  Now, moving forward in
time to r118390, a new scheme for striping was introduced that maintained a
blist allocator per device, but as noted in r318995, swapoff_one() was not
fully and correctly converted to the new scheme.  This change completes what
was started in r318995 by fixing the underlying bug in blst_meta_fill() that
stops swapoff_one() from simply performing a single blist_fill() operation.

Reviewed by:	kib
MFC after:	5 days
Differential Revision:	https://reviews.freebsd.org/D11043

sys/kern/subr_blist.c

@@ -769,6 +769,8 @@ blst_meta_fill(
 	int next_skip = ((u_int)skip / BLIST_META_RADIX);
 	int nblks = 0;
 
+	if (count > radix)
+		panic("blist_meta_fill: allocation too large");
 	if (count == radix || scan->u.bmu_avail == 0)  {
 		/*
 		 * ALL-ALLOCATED special case
@@ -800,9 +802,6 @@ blst_meta_fill(
 		radix /= BLIST_META_RADIX;
 	}
 
-	if (count > radix)
-		panic("blist_meta_fill: allocation too large");
-
 	i = (allocBlk - blk) / radix;
 	blk += i * radix;
 	i = i * next_skip + 1;

sys/vm/swap_pager.c

@@ -2271,7 +2271,7 @@ sys_swapoff(struct thread *td, struct swapoff_args *uap)
 static int
 swapoff_one(struct swdevt *sp, struct ucred *cred)
 {
-	u_long nblks, dvbase;
+	u_long nblks;
 #ifdef MAC
 	int error;
 #endif
@@ -2300,14 +2300,7 @@ swapoff_one(struct swdevt *sp, struct ucred *cred)
 	 */
 	mtx_lock(&sw_dev_mtx);
 	sp->sw_flags |= SW_CLOSING;
-	for (dvbase = 0; dvbase < nblks; dvbase += BLIST_BMAP_RADIX) {
+	swap_pager_avail -= blist_fill(sp->sw_blist, 0, nblks);
-		/*
-		 * blist_fill() cannot allocate more than BLIST_BMAP_RADIX
-		 * blocks per call.
-		 */
-		swap_pager_avail -= blist_fill(sp->sw_blist,
-		    dvbase, ulmin(nblks - dvbase, BLIST_BMAP_RADIX));
-	}
 	swap_total -= (vm_ooffset_t)nblks * PAGE_SIZE;
 	mtx_unlock(&sw_dev_mtx);