Use BUDDY_POOL() for regionlists (addresses a lockup)

The oh-so-smart idea from 39c2568e was
pretty dumb after all:

While testing with the low RAM config (16MB on 10GB), a lockop was found
with only ~45% of RAM occupied. The reason for the lockup was the
un-crammed 64KB (16bits) request for a regionlist with priority 4, which
was blocking all other requests.

So: No, trying to allocate something "just in case" is never a good
idea.

src/fellow_regionlist.h

@@ -51,16 +51,15 @@ struct regl {
 	struct buddy_off_extent	arr[];
 };
 
-// [0] crammed
-// [1] not crammed
-BUDDY_REQS(rl_rsv, 2);
+BUDDY_POOL(rl_pool, 4);	// XXX 4 good?
+BUDDY_POOL_GET_FUNC(rl_pool, static)
 
 struct regionlist {
 	unsigned			magic;
 #define REGIONLIST_MAGIC		0xeb869815
 	size_t				size;
 	VSTAILQ_HEAD(,regl)		head;
-	struct rl_rsv			rsv;
+	struct rl_pool			pool[1];
 };
 
 // usage: struct regl_stk(42)
@@ -145,12 +144,17 @@ init_regl(void)
 }
 
 static void
-regl_rsv(struct buddy_reqs *reqs)
+regl_fill(struct buddy_reqs *reqs, const void *priv)
 {
+	unsigned u;
+
+	CHECK_OBJ_NOTNULL(reqs, BUDDY_REQS_MAGIC);
+	(void) priv;
+
 	BUDDY_REQS_PRI(reqs, FEP_MEM_FREE);
-	AN(buddy_req_page(reqs, regl_bits, regl_bits_cram));
-	AN(buddy_req_page(reqs, regl_bits, 0));
-	(void) buddy_alloc_async(reqs);
+
+	for (u = 0; u < reqs->space; u++)
+		AN(buddy_req_page(reqs, regl_bits, regl_bits_cram));
 }
 
 static struct regl *
@@ -198,8 +202,7 @@ regionlist_alloc(buddy_t *membuddy)
 	INIT_OBJ(rl, REGIONLIST_MAGIC);
 	VSTAILQ_INIT(&rl->head);
 
-	BUDDY_REQS_INIT(&rl->rsv, membuddy);
-	regl_rsv(&rl->rsv.reqs);
+	BUDDY_POOL_INIT(rl->pool, membuddy, regl_fill, NULL);
 
 	r = regl_init(alloc, sizeof(*rl));
 	AN(r);
@@ -227,7 +230,7 @@ regionlist_append(struct regionlist *to, struct regionlist **fromp)
 
 	CHECK_OBJ_NOTNULL(to, REGIONLIST_MAGIC);
 	TAKE_OBJ_NOTNULL(from, fromp, REGIONLIST_MAGIC);
-	buddy_alloc_wait_done(&from->rsv.reqs);
+	BUDDY_POOL_FINI(from->pool);
 	to->size += from->size;
 	VSTAILQ_CONCAT(&to->head, &from->head);
 }
@@ -236,36 +239,16 @@ static struct regl *
 regionlist_extend(struct regionlist *rl)
 {
 	struct buddy_ptr_page alloc;
-	struct buddy_reqs *reqs;
 	struct regl *regl;
-	unsigned n;
 
 	CHECK_OBJ_NOTNULL(rl, REGIONLIST_MAGIC);
-	reqs = &rl->rsv.reqs;
 
-	n = buddy_alloc_async_ready(reqs);
-	if (n == 0)
-		n = buddy_alloc_async_wait(reqs);
-	AN(n);
-	alloc = buddy_get_next_ptr_page(reqs);
+	alloc = buddy_get_next_ptr_page(rl_pool_get(rl->pool, NULL));
 	AN(alloc.ptr);
-	if (buddy_reqs_next_ready(reqs) &&
-	    alloc.bits < regl_minbits) {
-		// the first request was crammed and we have an uncrammed
-		buddy_return1_ptr_page(reqs->buddy, &alloc);
-		alloc = buddy_get_next_ptr_page(reqs);
-		AN(alloc.ptr);
-	}
 
 	regl = regl_init(alloc, (size_t)0);
 	VSTAILQ_INSERT_TAIL(&rl->head, regl, list);
 
-	// issue the next async req
-	if (! buddy_reqs_next_ready(reqs)) {
-		buddy_alloc_wait_done(reqs);
-		regl_rsv(reqs);
-	}
-
 	return (regl);
 }
 
@@ -319,9 +302,8 @@ regionlist_free(struct regionlist **rlp, buddy_t *dskbuddy)
 
 	TAKE_OBJ_NOTNULL(rl, rlp, REGIONLIST_MAGIC);
 
-	membuddy = rl->rsv.reqs.buddy;
-	AN(membuddy);
-	buddy_alloc_wait_done(&rl->rsv.reqs);
+	membuddy = rl->pool->reqs[0].reqs.buddy;
+	BUDDY_POOL_FINI(rl->pool);
 
 	dskret = BUDDY_RETURNS_STK(dskbuddy, BUDDY_RETURNS_MAX);
 	memret = BUDDY_RETURNS_STK(membuddy, BUDDY_RETURNS_MAX);