Index: head/sys/geom/geom.h
===================================================================
--- head/sys/geom/geom.h
+++ head/sys/geom/geom.h
@@ -343,6 +343,7 @@
 int g_io_getattr(const char *attr, struct g_consumer *cp, int *len, void *ptr);
 int g_io_zonecmd(struct disk_zone_args *zone_args, struct g_consumer *cp);
 int g_io_flush(struct g_consumer *cp);
+int g_io_speedup(size_t shortage, u_int flags, size_t *resid, struct g_consumer *cp);
 int g_register_classifier(struct g_classifier_hook *hook);
 void g_unregister_classifier(struct g_classifier_hook *hook);
 void g_io_request(struct bio *bp, struct g_consumer *cp);
Index: head/sys/geom/geom_io.c
===================================================================
--- head/sys/geom/geom_io.c
+++ head/sys/geom/geom_io.c
@@ -340,6 +340,42 @@
 	return (error);
 }
 
+/*
+ * Send a BIO_SPEEDUP down the stack. This is used to tell the lower layers that
+ * the upper layers have detected a resource shortage. The lower layers are
+ * advised to stop delaying I/O that they might be holding for performance
+ * reasons and to schedule it (non-trims) or complete it successfully (trims) as
+ * quickly as it can. bio_length is the amount of the shortage.  This call
+ * should be non-blocking. bio_resid is used to communicate back if the lower
+ * layers couldn't find bio_length worth of I/O to schedule or discard. A length
+ * of 0 means to do as much as you can (schedule the h/w queues full, discard
+ * all trims). flags are a hint from the upper layers to the lower layers what
+ * operation should be done.
+ */
+int
+g_io_speedup(size_t shortage, u_int flags, size_t *resid, struct g_consumer *cp)
+{
+	struct bio *bp;
+	int error;
+
+	KASSERT((flags & (BIO_SPEEDUP_TRIM | BIO_SPEEDUP_WRITE)) != 0,
+	    ("Invalid flags passed to g_io_speedup: %#x", flags));
+	g_trace(G_T_BIO, "bio_speedup(%s, %zu, %#x)", cp->provider->name,
+	    shortage, flags);
+	bp = g_new_bio();
+	if (bp == NULL)
+		return (ENOMEM);
+	bp->bio_cmd = BIO_SPEEDUP;
+	bp->bio_length = shortage;
+	bp->bio_done = NULL;
+	bp->bio_flags |= flags;
+	g_io_request(bp, cp);
+	error = biowait(bp, "gflush");
+	*resid = bp->bio_resid;
+	g_destroy_bio(bp);
+	return (error);
+}
+
 int
 g_io_flush(struct g_consumer *cp)
 {
Index: head/sys/sys/bio.h
===================================================================
--- head/sys/sys/bio.h
+++ head/sys/sys/bio.h
@@ -53,6 +53,7 @@
 #define BIO_CMD1	0x07	/* Available for local hacks */
 #define BIO_CMD2	0x08	/* Available for local hacks */
 #define BIO_ZONE	0x09	/* Zone command */
+#define BIO_SPEEDUP	0x0a	/* Upper layers face shortage */
 
 /* bio_flags */
 #define BIO_ERROR	0x01	/* An error occurred processing this bio. */
@@ -69,6 +70,9 @@
 
 #define	PRINT_BIO_FLAGS "\20\7vlist\6transient_mapping\5unmapped" \
 	"\4ordered\3onqueue\2done\1error"
+
+#define BIO_SPEEDUP_WRITE	0x4000	/* Resource shortage at upper layers */
+#define BIO_SPEEDUP_TRIM	0x8000	/* Resource shortage at upper layers */
 
 #ifdef _KERNEL
 struct disk;