When logbuffer mempool is running low ...

kick the logwatcher first before potentially running into a synchronous
flush.

src/fellow_log.c

@@ -883,7 +883,7 @@ struct flw_need_why {
 	char	s[256];
 };
 static enum flw_need_e
-fellow_logwatcher_need(const struct fellow_fd *, struct flw_need_why *);
+fellow_logwatcher_need(struct fellow_fd *, struct flw_need_why *);
 
 #include "fellow_log_dle_chg.h"
 
@@ -3229,6 +3229,11 @@ logbuffer_addblks(struct fellow_fd *ffd,
 			else if (lbuf->n * 2 > lbuf->space)
 				kick = 1;
 		}
+		/* low water in mempool?
+		 */
+		if (canflush &&
+		    lbuf_mempool_avail(lbuf->mempool) < LBUF_MEMPOOL_SIZE)
+			kick = 1;
 
 		/* if we run short of disk blocks (25%), we want to
 		 * ref in order to apply frees
@@ -5721,9 +5726,9 @@ fellow_logwatcher_need_openlog(const struct fellow_logbuffer *lbuf,
 }
 
 static enum flw_need_e
-fellow_logwatcher_need(const struct fellow_fd *ffd, struct flw_need_why *why)
+fellow_logwatcher_need(struct fellow_fd *ffd, struct flw_need_why *why)
 {
-	const struct fellow_logbuffer *lbuf;
+	struct fellow_logbuffer *lbuf;
 	const struct stvfe_tune *tune;
 	enum flw_need_e need;
 	// XXX config?
@@ -5748,14 +5753,16 @@ fellow_logwatcher_need(const struct fellow_fd *ffd, struct flw_need_why *why)
 			return (need);
 	}
 
-	if (lbuf->space != 0 &&
-	    lbuf->space - lbuf->n <= thr_logbuffer_minfree)
+	if (lbuf->space == 0 || lbuf->n == 0)
+		return (FLW_NEED_NONE);
+
+	if (lbuf_mempool_avail(lbuf->mempool) < LBUF_MEMPOOL_SIZE)
 		return (FLW_NEED_FLUSH);
 
-	if (lbuf->space != 0 && lbuf->n != 0)
-		return (FLW_MAYFLUSH);
+	if (lbuf->space - lbuf->n <= thr_logbuffer_minfree)
+		return (FLW_NEED_FLUSH);
 
-	return (FLW_NEED_NONE);
+	return (FLW_MAYFLUSH);
 }
 
 /*