1 files changed, 16 insertions, 2 deletions

diff --git a/sys/vm/vm_fault.c b/sys/vm/vm_fault.c
index ca1ee1c..23e2ba0 100644
--- a/sys/vm/vm_fault.c
+++ b/sys/vm/vm_fault.c
@@ -779,15 +779,29 @@ readrest:
 		vm_page_flag_set(fs.m, PG_WRITEABLE);
 		vm_object_set_flag(fs.m->object,
 				   OBJ_WRITEABLE|OBJ_MIGHTBEDIRTY);
+
 		/*
 		 * If the fault is a write, we know that this page is being
-		 * written NOW. This will save on the pmap_is_modified() calls
-		 * later.
+		 * written NOW so dirty it explicitly to save on 
+		 * pmap_is_modified() calls later.
+		 *
+		 * If this is a NOSYNC mmap we do not want to set PG_NOSYNC
+		 * if the page is already dirty to prevent data written with
+		 * the expectation of being synced from not being synced.
+		 * Likewise if this entry does not request NOSYNC then make
+		 * sure the page isn't marked NOSYNC.  Applications sharing
+		 * data should use the same flags to avoid ping ponging.
 		 *
 		 * Also tell the backing pager, if any, that it should remove
 		 * any swap backing since the page is now dirty.
 		 */
 		if (fault_flags & VM_FAULT_DIRTY) {
+			if (fs.entry->eflags & MAP_ENTRY_NOSYNC) {
+				if (fs.m->dirty == 0)
+					vm_page_flag_set(fs.m, PG_NOSYNC);
+			} else {
+				vm_page_flag_clear(fs.m, PG_NOSYNC);
+			}
 			vm_page_dirty(fs.m);
 			vm_pager_page_unswapped(fs.m);
 		}