From: Alexander Bluhm <bluhm@openbsd.org>
Subject: bounce buffer mbuf defrag
To: tech@openbsd.org
Date: Wed, 28 Aug 2024 14:37:45 +0200

Hi,

In my tests I have seen packet drops vio_encap() when using bounce
buffers.  Some mbufs seem to be too fragmented for the pre allocated
bounce buffer pages.  Calling m_defrag() fixes the problem.

ok?

bluhm

Index: arch/amd64/amd64/bus_dma.c
===================================================================
RCS file: /data/mirror/openbsd/cvs/src/sys/arch/amd64/amd64/bus_dma.c,v
diff -u -p -r1.57 bus_dma.c
--- arch/amd64/amd64/bus_dma.c	22 Aug 2024 11:36:24 -0000	1.57
+++ arch/amd64/amd64/bus_dma.c	27 Aug 2024 20:48:12 -0000
@@ -726,7 +726,7 @@ _bus_dmamap_load_buffer(bus_dma_tag_t t,
 
 		if (use_bounce_buffer) {
 			if (page >= map->_dm_npages)
-				return (ENOMEM);
+				return (EFBIG);
 
 			off = vaddr & PAGE_MASK;
 			pg = map->_dm_pages[page];