Raise dsk alloc priority of logbuffer flushes with frees

Hopefully, this also contributes to a solution for #28

src/fellow_log.c

@@ -2198,11 +2198,23 @@ log_blocks_alloc_from_reqs(struct buddy_reqs *reqs,
 }
 
 static void
-logbuffer_fill_dskreq(struct buddy_reqs *reqs) {
+logbuffer_fill_dskreq(const struct fellow_logbuffer *lbuf,
+    struct buddy_reqs *reqs) {
 	unsigned i;
+	uint8_t pri;
 
+	CHECK_OBJ_NOTNULL(lbuf, FELLOW_LOGBUFFER_MAGIC);
 	CHECK_OBJ_NOTNULL(reqs, BUDDY_REQS_MAGIC);
 	buddy_alloc_wait_done(reqs);
+
+	if (lbuf->regions_to_free &&
+	    regionlist_used(lbuf->regions_to_free))
+		pri = FEP_DSK_LOG_PRI;
+	else
+		pri = FEP_DSK_LOG;
+
+	BUDDY_REQS_PRI(reqs, pri);
+
 	for (i = 0; i < reqs->space; i++)
 		AN(buddy_req_page(reqs, MIN_FELLOW_BITS, 0));
 	(void) buddy_alloc_async(reqs);
@@ -2228,7 +2240,7 @@ logbuffer_get_dskreqs(struct fellow_logbuffer *lbuf)
 		(void) buddy_alloc_async_wait(reqs);
 		if (buddy_reqs_next_ready(reqs))
 			return (reqs);			// ret2
-		logbuffer_fill_dskreq(reqs);
+		logbuffer_fill_dskreq(lbuf, reqs);
 
 		lbuf->active_reqs = ! lbuf->active_reqs;
 	}
@@ -2252,6 +2264,8 @@ logbuffer_alloc_some(struct fellow_logbuffer *lbuf,
 	AN(arr);
 	AN(n);
 
+	assert(logbuffer_can(lbuf, LBUF_CAN_FLUSH));
+
 	if (lbuf->logreg != NULL)
 		i = logblocks_alloc_from_logregion(lbuf->logreg, arr, n);
 	else
@@ -2299,8 +2313,7 @@ logbuffer_alloc_some(struct fellow_logbuffer *lbuf,
 		dskreqs = alloc.ptr;
 		for (i = 0; i < 2; i++) {
 			BUDDY_REQS_INIT(&(*dskreqs)[i], lbuf->dskbuddy);
-			BUDDY_REQS_PRI(&(*dskreqs)[i].reqs, FEP_DSK_LOG);
-			logbuffer_fill_dskreq(&(*dskreqs)[i].reqs);
+			logbuffer_fill_dskreq(lbuf, &(*dskreqs)[i].reqs);
 		}
 		lbuf->dskreqs = dskreqs;
 	}

src/fellow_pri.h

@@ -37,3 +37,4 @@
 #define FEP_ITER	4	// obj critical (oh lck)
 #define FEP_MEM_FREE	4	// regionlist
 #define FEP_DSK_LOG	4	//			logbuffer_alloc_some
+#define FEP_DSK_LOG_PRI 5	//			logbuffer_alloc_... free

src/fellow_regionlist.h

@@ -182,6 +182,18 @@ regionlist_alloc(buddy_t *membuddy)
 	return (rl);
 }
 
+static unsigned
+regionlist_used(const struct regionlist *rl)
+{
+	struct regl *r;
+
+	CHECK_OBJ_NOTNULL(rl, REGIONLIST_MAGIC);
+	r = VSTAILQ_FIRST(&rl->head);
+	if (r == NULL)
+		return (0);
+	return (r->n);
+}
+
 static void
 regionlist_append(struct regionlist *to, struct regionlist **fromp)
 {