mbuf: Don't support PAGE_SIZE < 4K

The Vax supported such things, but FreeBSD does not.  This further
implies that MJUMPAGESIZE > MCLBYTES so assert this and remove code
handling them being equal.

Reviewed by:	kp, imp, jhb
Sponsored by:	DARPA, AFRL
Differential Revision:	https://reviews.freebsd.org/D36320

sys/kern/kern_mbuf.c

@@ -63,6 +63,9 @@ __FBSDID("$FreeBSD$");
 #include <vm/uma.h>
 #include <vm/uma_dbg.h>
 
+_Static_assert(MJUMPAGESIZE > MCLBYTES,
+    "Cluster must be smaller than a jumbo page");
+
 /*
  * In FreeBSD, Mbufs and Mbuf Clusters are allocated from UMA
  * Zones.

sys/sys/mbuf.h

@@ -894,11 +894,9 @@ m_gettype(int size)
 	case MCLBYTES:
 		type = EXT_CLUSTER;
 		break;
-#if MJUMPAGESIZE != MCLBYTES
 	case MJUMPAGESIZE:
 		type = EXT_JUMBOP;
 		break;
-#endif
 	case MJUM9BYTES:
 		type = EXT_JUMBO9;
 		break;
@@ -944,11 +942,9 @@ m_getzone(int size)
 	case MCLBYTES:
 		zone = zone_clust;
 		break;
-#if MJUMPAGESIZE != MCLBYTES
 	case MJUMPAGESIZE:
 		zone = zone_jumbop;
 		break;
-#endif
 	case MJUM9BYTES:
 		zone = zone_jumbo9;
 		break;
@@ -1068,11 +1064,9 @@ m_cljset(struct mbuf *m, void *cl, int type)
 	case EXT_CLUSTER:
 		size = MCLBYTES;
 		break;
-#if MJUMPAGESIZE != MCLBYTES
 	case EXT_JUMBOP:
 		size = MJUMPAGESIZE;
 		break;
-#endif
 	case EXT_JUMBO9:
 		size = MJUM9BYTES;
 		break;

sys/sys/param.h

@@ -200,9 +200,7 @@
 
 #define MCLBYTES	(1 << MCLSHIFT)	/* size of an mbuf cluster */
 
-#if PAGE_SIZE < 2048
-#define	MJUMPAGESIZE	MCLBYTES
-#elif PAGE_SIZE <= 8192
+#if PAGE_SIZE <= 8192
 #define	MJUMPAGESIZE	PAGE_SIZE
 #else
 #define	MJUMPAGESIZE	(8 * 1024)