Fixed a problem that the UPAGES of a process were being run down

in a suboptimal manner.  I had also noticed some panics that appeared
to be at least superficially caused by this problem.  Also, included
are some minor mods to support more general handling of page table page
faulting.  More details in a future commit.

1 files changed, 41 insertions, 7 deletions

diff --git a/sys/vm/vm_glue.c b/sys/vm/vm_glue.c
index 999c356..96abfb2 100644
--- a/sys/vm/vm_glue.c
+++ b/sys/vm/vm_glue.c
@@ -59,7 +59,7 @@
  * any improvements or extensions that they make and grant Carnegie the
  * rights to redistribute these changes.
  *
- * $Id: vm_glue.c,v 1.42 1996/03/09 06:57:53 dyson Exp $
+ * $Id: vm_glue.c,v 1.43 1996/03/11 06:11:39 hsu Exp $
  */
 
 #include "opt_ddb.h"
@@ -245,39 +245,70 @@ vm_fork(p1, p2)
 	map = &p2->p_vmspace->vm_map;
 	pvp = &p2->p_vmspace->vm_pmap;
 
-	/* get new pagetables and kernel stack */
+	/*
+	 * allocate object for the upages
+	 */
+	p2->p_vmspace->vm_upages_obj = vm_object_allocate( OBJT_DEFAULT,
+		UPAGES);
+
+	/*
+	 * put upages into the address space
+	 */
+	error = vm_map_find(map, p2->p_vmspace->vm_upages_obj, 0,
+		&addr, UPT_MIN_ADDRESS - addr, FALSE, VM_PROT_ALL,
+		VM_PROT_ALL, 0);
+	if (error != KERN_SUCCESS)
+		panic("vm_fork: vm_map_find (UPAGES) failed, addr=0x%x, error=%d", addr, error);
+
+	addr += UPAGES * PAGE_SIZE;
+	/* allocate space for page tables */
 	error = vm_map_find(map, NULL, 0, &addr, UPT_MAX_ADDRESS - addr, FALSE,
 		VM_PROT_ALL, VM_PROT_ALL, 0);
 	if (error != KERN_SUCCESS)
-		panic("vm_fork: vm_map_find failed, addr=0x%x, error=%d", addr, error);
+		panic("vm_fork: vm_map_find (PTES) failed, addr=0x%x, error=%d", addr, error);
 
 	/* get a kernel virtual address for the UPAGES for this proc */
 	up = (struct user *) kmem_alloc_pageable(u_map, UPAGES * PAGE_SIZE);
 	if (up == NULL)
 		panic("vm_fork: u_map allocation failed");
 
-	p2->p_vmspace->vm_upages_obj = vm_object_allocate( OBJT_DEFAULT,
-		UPAGES);
-
+	/*
+	 * create a pagetable page for the UPAGES in the process address space
+	 */
 	ptaddr = trunc_page((u_int) vtopte(kstack));
 	(void) vm_fault(map, ptaddr, VM_PROT_READ|VM_PROT_WRITE, FALSE);
 	ptpa = pmap_extract(pvp, ptaddr);
 	if (ptpa == 0) {
 		panic("vm_fork: no pte for UPAGES");
 	}
+
+	/*
+	 * hold the page table page for the kernel stack, and fault them in
+	 */
 	stkm = PHYS_TO_VM_PAGE(ptpa);
 	vm_page_hold(stkm);
 
 	for(i=0;i<UPAGES;i++) {
 		vm_page_t m;
 
+		/*
+		 * Get a kernel stack page
+		 */
 		while ((m = vm_page_alloc(p2->p_vmspace->vm_upages_obj,
 			i, VM_ALLOC_NORMAL)) == NULL) {
 			VM_WAIT;
 		}
 
+		/*
+		 * Wire the page
+		 */
 		vm_page_wire(m);
 		m->flags &= ~PG_BUSY;
+
+		/*
+		 * Enter the page into both the kernel and the process
+		 * address space.
+		 */
 		pmap_enter( pvp, (vm_offset_t) kstack + i * PAGE_SIZE,
 			VM_PAGE_TO_PHYS(m), VM_PROT_READ|VM_PROT_WRITE, 1);
 		pmap_kenter(((vm_offset_t) up) + i * PAGE_SIZE,
@@ -285,9 +316,12 @@ vm_fork(p1, p2)
 		m->flags &= ~PG_ZERO;
 		m->valid = VM_PAGE_BITS_ALL;
 	}
+	/*
+	 * The page table page for the kernel stack should be held in memory
+	 * now.
+	 */
 	vm_page_unhold(stkm);
 
-
 	p2->p_addr = up;
 
 	/*