MFC r323973,324087

  Optimize vm_page_try_to_free().  Specifically, the call to pmap_remove_all()
  can be avoided when the page's containing object has a reference count of
  zero.  (If the object has a reference count of zero, then none of its pages
  can possibly be mapped.)

  Address nearby style issues in vm_page_try_to_free(), and change its
  return type to "bool".

  Optimize vm_object_page_remove() by eliminating pointless calls to
  pmap_remove_all().  If the object to which a page belongs has no
  references, then that page cannot possibly be mapped.

(cherry picked from commit 2d2427db5b735ecdb6fe8ad9251f524b4260bb6a)

3 files changed, 18 insertions, 14 deletions

diff --git a/sys/vm/vm_object.c b/sys/vm/vm_object.c
index ccac79a..c7c5dfa 100644
--- a/sys/vm/vm_object.c
+++ b/sys/vm/vm_object.c
@@ -1934,7 +1934,8 @@ again:
 			goto again;
 		}
 		if (p->wire_count != 0) {
-			if ((options & OBJPR_NOTMAPPED) == 0)
+			if ((options & OBJPR_NOTMAPPED) == 0 &&
+			    object->ref_count != 0)
 				pmap_remove_all(p);
 			if ((options & OBJPR_CLEANONLY) == 0) {
 				p->valid = 0;
@@ -1951,12 +1952,13 @@ again:
 		KASSERT((p->flags & PG_FICTITIOUS) == 0,
 		    ("vm_object_page_remove: page %p is fictitious", p));
 		if ((options & OBJPR_CLEANONLY) != 0 && p->valid != 0) {
-			if ((options & OBJPR_NOTMAPPED) == 0)
+			if ((options & OBJPR_NOTMAPPED) == 0 &&
+			    object->ref_count != 0)
 				pmap_remove_write(p);
-			if (p->dirty)
+			if (p->dirty != 0)
 				continue;
 		}
-		if ((options & OBJPR_NOTMAPPED) == 0)
+		if ((options & OBJPR_NOTMAPPED) == 0 && object->ref_count != 0)
 			pmap_remove_all(p);
 		vm_page_free(p);
 	}
diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
index 08203f2..155d1a8 100644
--- a/sys/vm/vm_page.c
+++ b/sys/vm/vm_page.c
@@ -3056,23 +3056,25 @@ vm_page_launder(vm_page_t m)
  * vm_page_try_to_free()
  *
  *	Attempt to free the page.  If we cannot free it, we do nothing.
- *	1 is returned on success, 0 on failure.
+ *	true is returned on success, false on failure.
  */
-int
+bool
 vm_page_try_to_free(vm_page_t m)
 {
 
-	vm_page_lock_assert(m, MA_OWNED);
+	vm_page_assert_locked(m);
 	if (m->object != NULL)
 		VM_OBJECT_ASSERT_WLOCKED(m->object);
-	if (m->dirty || m->hold_count || m->wire_count ||
+	if (m->dirty != 0 || m->hold_count != 0 || m->wire_count != 0 ||
 	    (m->oflags & VPO_UNMANAGED) != 0 || vm_page_busied(m))
-		return (0);
-	pmap_remove_all(m);
-	if (m->dirty)
-		return (0);
+		return (false);
+	if (m->object != NULL && m->object->ref_count != 0) {
+		pmap_remove_all(m);
+		if (m->dirty != 0)
+			return (false);
+	}
 	vm_page_free(m);
-	return (1);
+	return (true);
 }
 
 /*
diff --git a/sys/vm/vm_page.h b/sys/vm/vm_page.h
index 3cc0fee..e0ae041 100644
--- a/sys/vm/vm_page.h
+++ b/sys/vm/vm_page.h
@@ -456,7 +456,6 @@ void vm_page_change_lock(vm_page_t m, struct mtx **mtx);
 vm_page_t vm_page_grab (vm_object_t, vm_pindex_t, int);
 int vm_page_grab_pages(vm_object_t object, vm_pindex_t pindex, int allocflags,
     vm_page_t *ma, int count);
-int vm_page_try_to_free (vm_page_t);
 void vm_page_deactivate (vm_page_t);
 void vm_page_deactivate_noreuse(vm_page_t);
 void vm_page_dequeue(vm_page_t m);
@@ -492,6 +491,7 @@ void vm_page_set_valid_range(vm_page_t m, int base, int size);
 int vm_page_sleep_if_busy(vm_page_t m, const char *msg);
 vm_offset_t vm_page_startup(vm_offset_t vaddr);
 void vm_page_sunbusy(vm_page_t m);
+bool vm_page_try_to_free(vm_page_t m);
 int vm_page_trysbusy(vm_page_t m);
 void vm_page_unhold_pages(vm_page_t *ma, int count);
 boolean_t vm_page_unwire(vm_page_t m, uint8_t queue);