Add sysctl vm.md_malloc_wait, non-zero value of which switches malloc-backed

md(4) to using M_WAITOK malloc calls.

M_NOWAITOK allocations may fail when enough memory could be freed, but not
immediately. E.g. SU UFS becomes quite unhappy when metadata write return
error, that would happen for failed malloc() call.

Reported and tested by:	pho
MFC after:	1 week

1 files changed, 8 insertions, 3 deletions

diff --git a/sys/dev/md/md.c b/sys/dev/md/md.c
index 6c3484e..314e289 100644
--- a/sys/dev/md/md.c
+++ b/sys/dev/md/md.c
@@ -103,6 +103,8 @@ static MALLOC_DEFINE(M_MDSECT, "md_sectors", "Memory Disk Sectors");
 
 static int md_debug;
 SYSCTL_INT(_debug, OID_AUTO, mddebug, CTLFLAG_RW, &md_debug, 0, "");
+static int md_malloc_wait;
+SYSCTL_INT(_vm, OID_AUTO, md_malloc_wait, CTLFLAG_RW, &md_malloc_wait, 0, "");
 
 #if defined(MD_ROOT) && defined(MD_ROOT_SIZE)
 /*
@@ -208,11 +210,12 @@ new_indir(u_int shift)
 {
 	struct indir *ip;
 
-	ip = malloc(sizeof *ip, M_MD, M_NOWAIT | M_ZERO);
+	ip = malloc(sizeof *ip, M_MD, (md_malloc_wait ? M_WAITOK : M_NOWAIT)
+	    | M_ZERO);
 	if (ip == NULL)
 		return (NULL);
 	ip->array = malloc(sizeof(uintptr_t) * NINDIR,
-	    M_MDSECT, M_NOWAIT | M_ZERO);
+	    M_MDSECT, (md_malloc_wait ? M_WAITOK : M_NOWAIT) | M_ZERO);
 	if (ip->array == NULL) {
 		free(ip, M_MD);
 		return (NULL);
@@ -456,6 +459,7 @@ mdstart_malloc(struct md_s *sc, struct bio *bp)
 			} else {
 				if (osp <= 255) {
 					sp = (uintptr_t)uma_zalloc(sc->uma,
+					    md_malloc_wait ? M_WAITOK :
 					    M_NOWAIT);
 					if (sp == 0) {
 						error = ENOSPC;
@@ -850,7 +854,8 @@ mdcreate_malloc(struct md_s *sc, struct md_ioctl *mdio)
 
 		nsectors = sc->mediasize / sc->sectorsize;
 		for (u = 0; u < nsectors; u++) {
-			sp = (uintptr_t)uma_zalloc(sc->uma, M_NOWAIT | M_ZERO);
+			sp = (uintptr_t)uma_zalloc(sc->uma, md_malloc_wait ?
+			    M_WAITOK : M_NOWAIT | M_ZERO);
 			if (sp != 0)
 				error = s_write(sc->indir, u, sp);
 			else