Regionlist overhaul: Refactor regionlist cram calculation

src/fellow_regionlist.h

@@ -103,29 +103,45 @@ do {									\
 	regionlist_onlystk_add(name, o, s);				\
 } while(0)
 
-static struct regl *
-regl_alloc_bits(buddy_t *membuddy, const uint8_t bits, int8_t cram,
-    struct regionlist **rlp)
+static uint8_t regl_minbits;
+static void __attribute__((constructor))
+init_regl(void)
 {
-	struct buddy_ptr_page alloc;
-	struct regionlist *rl;
-	struct regl *r;
-	int8_t c;
-	size_t sz, b;
+	unsigned b =
+	    log2up(2 * sizeof(struct regl) + sizeof(struct regionlist));
+
+	assert(b <= UINT8_MAX);
+	regl_minbits = (typeof(regl_minbits))b;
+}
 
-	sz = 2 * sizeof *r + sizeof *rl;
-	b = log2up(sz);
-	assert(bits >= b);
+static int8_t
+regl_cram(const uint8_t bits, int8_t cram)
+{
+	int8_t c;
 
+	assert(bits > regl_minbits);
 	// should we also support negative cram?
 	assert(cram >= 0);
 	assert(bits < INT8_MAX);
-	c = (int8_t)(bits - (typeof(bits))b);
+	c = (int8_t)(bits - regl_minbits);
 	assert(c >= 0);
 	if (cram > c)
 		cram = c;
 
-	alloc = buddy_alloc1_ptr_page_wait(membuddy, FEP_MEM_FREE, bits, cram);
+	return (cram);
+}
+
+static struct regl *
+regl_alloc_bits(buddy_t *membuddy, const uint8_t bits, int8_t cram,
+    struct regionlist **rlp)
+{
+	struct buddy_ptr_page alloc;
+	struct regionlist *rl;
+	struct regl *r;
+	size_t sz, b;
+
+	alloc = buddy_alloc1_ptr_page_wait(membuddy, FEP_MEM_FREE, bits,
+	    regl_cram(bits, cram));
 	AN(alloc.ptr);
 
 	sz = (size_t)1 << alloc.bits;