Move CPU_ABSENT() macro to smp.h, where it belongs anyway. It will be

defined to 0 in the non-SMP case, which very much makes sense as it
permits its usage in per-CPU initialization loops (for an example, check
out subr_mbuf.c).
  Further, on a UP system, make mb_alloc always use the first per-CPU
container, regardless of cpuid (i.e. remove reliability on cpuid in the
UP case).

Requested by: alfred

sys/kern/subr_mbuf.c

@@ -61,21 +61,6 @@
 #define	NCPU	MAXCPU
 #endif
 
-/*
- * Macros allowing us to determine whether or not a given CPU's container
- * should be configured during mb_init().
- * XXX: Eventually we may want to provide hooks for CPU spinon/spinoff that
- *      will allow us to configure the containers on spinon/spinoff. As it
- *      stands, booting with CPU x disactivated and activating CPU x only
- *      after bootup will lead to disaster and CPU x's container will be
- *      uninitialized.
- */
-#ifdef	SMP
-#define	CPU_ABSENT(x)	((all_cpus & (1 << x)) == 0)
-#else
-#define	CPU_ABSENT(x)	0
-#endif
-
 /*
  * The mbuf allocator is heavily based on Alfred Perlstein's
  * (alfred@FreeBSD.org) "memcache" allocator which is itself based
@@ -213,7 +198,11 @@ struct	mtx		mbuf_gen, mbuf_pcpu[NCPU];
 /*
  * Local macros for internal allocator structure manipulations.
  */
+#ifdef SMP
 #define	MB_GET_PCPU_LIST(mb_lst)	  (mb_lst)->ml_cntlst[PCPU_GET(cpuid)]
+#else
+#define	MB_GET_PCPU_LIST(mb_lst)	  (mb_lst)->ml_cntlst[0]
+#endif
 
 #define	MB_GET_PCPU_LIST_NUM(mb_lst, num) (mb_lst)->ml_cntlst[(num)]
 

sys/sys/smp.h

@@ -27,6 +27,13 @@ extern u_int all_cpus;
 extern volatile u_int started_cpus;
 extern volatile u_int stopped_cpus;
 
+/*
+ * Macro allowing us to determine whether a CPU is absent at any given
+ * time, thus permitting us to configure sparse maps of cpuid-dependent
+ * (per-CPU) structures.
+ */
+#define	CPU_ABSENT(x_cpu)	((all_cpus & (1 << (x_cpu))) == 0)
+
 /*
  * Machine dependent functions used to initialize MP support.
  *
@@ -54,7 +61,8 @@ void	smp_rendezvous(void (*)(void *),
 		       void (*)(void *),
 		       void (*)(void *),
 		       void *arg);
-
+#else /* SMP */
+#define	CPU_ABSENT(x_cpu)	(0)
 #endif /* SMP */
 #endif /* !LOCORE */
 #endif /* _KERNEL */