Index: sys/net/iflib.c
===================================================================
--- sys/net/iflib.c
+++ sys/net/iflib.c
@@ -334,6 +334,7 @@
 #endif
 	uint64_t	ift_no_tx_dma_setup;
 	uint64_t	ift_no_desc_avail;
+	uint64_t	ift_mbuf_collapse_failed;
 	uint64_t	ift_mbuf_defrag_failed;
 	uint64_t	ift_mbuf_defrag;
 	uint64_t	ift_map_failed;
@@ -2257,7 +2258,7 @@
 		txq->ift_in_use = txq->ift_gen = txq->ift_cidx = txq->ift_pidx = txq->ift_no_desc_avail = 0;
 		txq->ift_closed = txq->ift_mbuf_defrag = txq->ift_mbuf_defrag_failed = 0;
 		txq->ift_no_tx_dma_setup = txq->ift_txd_encap_efbig = txq->ift_map_failed = 0;
-		txq->ift_pullups = 0;
+		txq->ift_pullups = txq->ift_mbuf_collapse_failed = 0;
 		ifmp_ring_reset_stats(txq->ift_br);
 		for (j = 0, di = txq->ift_ifdi; j < ctx->ifc_nhwtxqs; j++, di++)
 			bzero((void *)di->idi_vaddr, di->idi_size);
@@ -3087,13 +3088,18 @@
 		switch (err) {
 		case EFBIG:
 			/* try collapse once and defrag once */
-			if (remap == 0)
+			if (remap == 0) {
 				m_head = m_collapse(*m_headp, M_NOWAIT, max_segs);
+				if (m_head == NULL) {
+					txq->ift_mbuf_collapse_failed++;
+					remap++;
+				}
+			}
 			if (remap == 1)
 				m_head = m_defrag(*m_headp, M_NOWAIT);
-			remap++;
-			if (__predict_false(m_head == NULL))
+			if (__predict_false(m_head == NULL || remap > 1))
 				goto defrag_failed;
+			remap++;
 			txq->ift_mbuf_defrag++;
 			*m_headp = m_head;
 			goto retry;
@@ -4144,7 +4150,9 @@
 		scctx->isc_tx_tso_size_max = FREEBSD_TSO_SIZE_MAX;
 
 	/* TSO parameters - dig these out of the data sheet - simply correspond to tag setup */
-	ifp->if_hw_tsomaxsegcount = scctx->isc_tx_tso_segments_max;
+
+	/* use one segment less to avoid calling m_collapse/m_defrag */
+	ifp->if_hw_tsomaxsegcount = scctx->isc_tx_tso_segments_max - 1;
 	ifp->if_hw_tsomax = scctx->isc_tx_tso_size_max;
 	ifp->if_hw_tsomaxsegsize = scctx->isc_tx_tso_segsize_max;
 	if (scctx->isc_rss_table_size == 0)
@@ -5515,6 +5523,9 @@
 		SYSCTL_ADD_QUAD(ctx_list, queue_list, OID_AUTO, "mbuf_defrag_failed",
 				   CTLFLAG_RD,
 				   &txq->ift_mbuf_defrag_failed, "# of times m_defrag failed");
+		SYSCTL_ADD_QUAD(ctx_list, queue_list, OID_AUTO, "mbuf_collapse_failed",
+				   CTLFLAG_RD,
+				   &txq->ift_mbuf_collapse_failed, "# of times m_collapse failed");
 		SYSCTL_ADD_QUAD(ctx_list, queue_list, OID_AUTO, "no_desc_avail",
 				   CTLFLAG_RD,
 				   &txq->ift_no_desc_avail, "# of times no descriptors were available");