PVN_GETPAGE_{SZ,NUM} are misnamed and unnecessarily complicated
There is really no reason to not allow 8 pages all the time.  With the
current logic, we get the following:
Assuming 4kB pages (x86):
    _SZ  = ptob(8) /* 32kB */
    _NUM = 8
Assuming 8kB pages (sparc):
    _SZ  = ptob(8) /* 64kB */
    _NUM = 8
We'd have to deal with 16kB base pages in order for the _NUM #define to not
be 8 (it'd be 4 in that case).  So, in the spirit of simplicity, let's just
always grab 8 pages as there are no interesting systems with 16kB+ base pages.
Finally, the defines are poorly named.

@@ -76,27 +76,16 @@
 #include <sys/zone.h>
 #include <sys/shm_impl.h>
 
 /*
  * segvn_fault needs a temporary page list array.  To avoid calling kmem all
- * the time, it creates a small (PVN_GETPAGE_NUM entry) array and uses it if
- * it can.  In the rare case when this page list is not large enough, it
- * goes and gets a large enough array from kmem.
- *
- * This small page list array covers either 8 pages or 64kB worth of pages -
- * whichever is smaller.
+ * the time, it creates a small (FAULT_TMP_PAGES_NUM entry) array and uses
+ * it if it can.  In the rare case when this page list is not large enough,
+ * it goes and gets a large enough array from kmem.
  */
-#define PVN_MAX_GETPAGE_SZ      0x10000
-#define PVN_MAX_GETPAGE_NUM     0x8
-
-#if PVN_MAX_GETPAGE_SZ > PVN_MAX_GETPAGE_NUM * PAGESIZE
-#define PVN_GETPAGE_SZ  ptob(PVN_MAX_GETPAGE_NUM)
-#define PVN_GETPAGE_NUM PVN_MAX_GETPAGE_NUM
-#else
-#define PVN_GETPAGE_SZ  PVN_MAX_GETPAGE_SZ
-#define PVN_GETPAGE_NUM btop(PVN_MAX_GETPAGE_SZ)
-#endif
+#define FAULT_TMP_PAGES_NUM     0x8
+#define FAULT_TMP_PAGES_SZ      ptob(FAULT_TMP_PAGES_NUM)
 
 /*
  * Private seg op routines.
  */
 static int      segvn_dup(struct seg *seg, struct seg *newseg);

@@ -4923,11 +4912,11 @@
         u_offset_t off;
         caddr_t a;
         struct vpage *vpage;
         uint_t vpprot, prot;
         int err;
-        page_t *pl[PVN_GETPAGE_NUM + 1];
+        page_t *pl[FAULT_TMP_PAGES_NUM + 1];
         size_t plsz, pl_alloc_sz;
         size_t page;
         ulong_t anon_index;
         struct anon_map *amp;
         int dogetpage = 0;

@@ -5362,11 +5351,11 @@
 
                 if (dogetpage) {
                         enum seg_rw arw;
                         struct as *as = seg->s_as;
 
-                        if (len > ptob((sizeof (pl) / sizeof (pl[0])) - 1)) {
+                        if (len > FAULT_TMP_PAGES_SZ) {
                                 /*
                                  * Page list won't fit in local array,
                                  * allocate one of the needed size.
                                  */
                                 pl_alloc_sz =

@@ -5390,11 +5379,11 @@
                         } else {
                                 /*
                                  * Ask VOP_GETPAGE to return adjacent pages
                                  * within the segment.
                                  */
-                                plsz = MIN((size_t)PVN_GETPAGE_SZ, (size_t)
+                                plsz = MIN((size_t)FAULT_TMP_PAGES_SZ, (size_t)
                                     ((seg->s_base + seg->s_size) - addr));
                                 ASSERT((addr + plsz) <=
                                     (seg->s_base + seg->s_size));
                         }