Index: sys/amd64/include/pmap.h
===================================================================
--- sys/amd64/include/pmap.h	(revision 246277)
+++ sys/amd64/include/pmap.h	(working copy)
@@ -113,13 +113,7 @@
 	((unsigned long)(l2) << PDRSHIFT) | \
 	((unsigned long)(l1) << PAGE_SHIFT))
 
-/* Initial number of kernel page tables. */
-#ifndef NKPT
-#define	NKPT		32
-#endif
-
 #define NKPML4E		1		/* number of kernel PML4 slots */
-#define NKPDPE		howmany(NKPT, NPDEPG)/* number of kernel PDP slots */
 
 #define	NUPML4E		(NPML4EPG/2)	/* number of userland PML4 pages */
 #define	NUPDPE		(NUPML4E*NPDPEPG)/* number of userland PDP pages */
@@ -181,6 +175,7 @@
 #define	PML4map		((pd_entry_t *)(addr_PML4map))
 #define	PML4pml4e	((pd_entry_t *)(addr_PML4pml4e))
 
+extern int nkpt;		/* Initial number of kernel page tables */
 extern u_int64_t KPDPphys;	/* physical address of kernel level 3 */
 extern u_int64_t KPML4phys;	/* physical address of kernel level 4 */
 
Index: sys/amd64/amd64/minidump_machdep.c
===================================================================
--- sys/amd64/amd64/minidump_machdep.c	(revision 246277)
+++ sys/amd64/amd64/minidump_machdep.c	(working copy)
@@ -232,7 +232,7 @@
 	/* Walk page table pages, set bits in vm_page_dump */
 	pmapsize = 0;
 	pdp = (uint64_t *)PHYS_TO_DMAP(KPDPphys);
-	for (va = VM_MIN_KERNEL_ADDRESS; va < MAX(KERNBASE + NKPT * NBPDR,
+	for (va = VM_MIN_KERNEL_ADDRESS; va < MAX(KERNBASE + nkpt * NBPDR,
 	    kernel_vm_end); ) {
 		/*
 		 * We always write a page, even if it is zero. Each
@@ -364,7 +364,7 @@
 	/* Dump kernel page directory pages */
 	bzero(fakepd, sizeof(fakepd));
 	pdp = (uint64_t *)PHYS_TO_DMAP(KPDPphys);
-	for (va = VM_MIN_KERNEL_ADDRESS; va < MAX(KERNBASE + NKPT * NBPDR,
+	for (va = VM_MIN_KERNEL_ADDRESS; va < MAX(KERNBASE + nkpt * NBPDR,
 	    kernel_vm_end); va += NBPDP) {
 		i = (va >> PDPSHIFT) & ((1ul << NPDPEPGSHIFT) - 1);
 
Index: sys/amd64/amd64/pmap.c
===================================================================
--- sys/amd64/amd64/pmap.c	(revision 246277)
+++ sys/amd64/amd64/pmap.c	(working copy)
@@ -202,6 +202,10 @@
 vm_offset_t virtual_avail;	/* VA of first avail page (after kernel bss) */
 vm_offset_t virtual_end;	/* VA of last avail page (end of kernel AS) */
 
+int nkpt;
+SYSCTL_INT(_machdep, OID_AUTO, nkpt, CTLFLAG_RD, &nkpt, 0,
+    "Number of kernel page table pages allocated on bootup");
+
 static int ndmpdp;
 static vm_paddr_t dmaplimit;
 vm_offset_t kernel_vm_end = VM_MIN_KERNEL_ADDRESS;
@@ -495,17 +499,42 @@
 
 CTASSERT(powerof2(NDMPML4E));
 
+/* number of kernel PDP slots */
+#define	NKPDPE(ptpgs)		howmany((ptpgs), NPDEPG)
+
 static void
+nkpt_init(vm_paddr_t addr)
+{
+	int pt_pages;
+	
+#ifdef NKPT
+	pt_pages = NKPT;
+#else
+	pt_pages = howmany(addr, 1 << PDRSHIFT);
+	pt_pages += NKPDPE(pt_pages);
+
+	/*
+	 * Add some slop beyond the bare minimum required for bootstrapping
+	 * the kernel.
+	 *
+	 * This is quite important when allocating KVA for kernel modules.
+	 * The modules are required to be linked in the negative 2GB of
+	 * the address space.  If we run out of KVA in this region then
+	 * pmap_growkernel() will need to allocate page table pages to map
+	 * the entire 512GB of KVA space which is an unnecessary tax on
+	 * physical memory.
+	 */
+	pt_pages += 4;		/* 8MB additional slop for kernel modules */
+#endif
+	nkpt = pt_pages;
+}
+
+static void
 create_pagetables(vm_paddr_t *firstaddr)
 {
-	int i, j, ndm1g;
+	int i, j, ndm1g, nkpdpe;
 
-	/* Allocate pages */
-	KPTphys = allocpages(firstaddr, NKPT);
-	KPML4phys = allocpages(firstaddr, 1);
-	KPDPphys = allocpages(firstaddr, NKPML4E);
-	KPDphys = allocpages(firstaddr, NKPDPE);
-
+	/* Allocate page table pages for the direct map */
 	ndmpdp = (ptoa(Maxmem) + NBPDP - 1) >> PDPSHIFT;
 	if (ndmpdp < 4)		/* Minimum 4GB of dirmap */
 		ndmpdp = 4;
@@ -517,6 +546,22 @@
 		DMPDphys = allocpages(firstaddr, ndmpdp - ndm1g);
 	dmaplimit = (vm_paddr_t)ndmpdp << PDPSHIFT;
 
+	/* Allocate pages */
+	KPML4phys = allocpages(firstaddr, 1);
+	KPDPphys = allocpages(firstaddr, NKPML4E);
+
+	/*
+	 * Allocate the initial number of kernel page table pages required to
+	 * bootstrap.  We defer this until after all memory-size dependent
+	 * allocations are done (e.g. direct map), so that we don't have to
+	 * build in too much slop in our estimate.
+	 */
+	nkpt_init(*firstaddr);
+	nkpdpe = NKPDPE(nkpt);
+
+	KPTphys = allocpages(firstaddr, nkpt);
+	KPDphys = allocpages(firstaddr, nkpdpe);
+
 	/* Fill in the underlying page table pages */
 	/* Read-only from zero to physfree */
 	/* XXX not fully used, underneath 2M pages */
@@ -526,7 +571,7 @@
 	}
 
 	/* Now map the page tables at their location within PTmap */
-	for (i = 0; i < NKPT; i++) {
+	for (i = 0; i < nkpt; i++) {
 		((pd_entry_t *)KPDphys)[i] = KPTphys + (i << PAGE_SHIFT);
 		((pd_entry_t *)KPDphys)[i] |= PG_RW | PG_V;
 	}
@@ -539,7 +584,7 @@
 	}
 
 	/* And connect up the PD to the PDP */
-	for (i = 0; i < NKPDPE; i++) {
+	for (i = 0; i < nkpdpe; i++) {
 		((pdp_entry_t *)KPDPphys)[i + KPDPI] = KPDphys +
 		    (i << PAGE_SHIFT);
 		((pdp_entry_t *)KPDPphys)[i + KPDPI] |= PG_RW | PG_V | PG_U;
@@ -768,7 +813,7 @@
 	 * Initialize the vm page array entries for the kernel pmap's
 	 * page table pages.
 	 */ 
-	for (i = 0; i < NKPT; i++) {
+	for (i = 0; i < nkpt; i++) {
 		mpte = PHYS_TO_VM_PAGE(KPTphys + (i << PAGE_SHIFT));
 		KASSERT(mpte >= vm_page_array &&
 		    mpte < &vm_page_array[vm_page_array_size],
@@ -1995,7 +2040,7 @@
 	 * any new kernel page table pages between "kernel_vm_end" and
 	 * "KERNBASE".
 	 */
-	if (KERNBASE < addr && addr <= KERNBASE + NKPT * NBPDR)
+	if (KERNBASE < addr && addr <= KERNBASE + nkpt * NBPDR)
 		return;
 
 	addr = roundup2(addr, NBPDR);