The synchronization provided by vm object locking has eliminated the

need for most calls to vm_page_busy().  Specifically, most calls to
vm_page_busy() occur immediately prior to a call to vm_page_remove().
In such cases, the containing vm object is locked across both calls.
Consequently, the setting of the vm page's PG_BUSY flag is not even
visible to other threads that are following the synchronization
protocol.

This change (1) eliminates the calls to vm_page_busy() that
immediately precede a call to vm_page_remove() or functions, such as
vm_page_free() and vm_page_rename(), that call it and (2) relaxes the
requirement in vm_page_remove() that the vm page's PG_BUSY flag is
set.  Now, the vm page's PG_BUSY flag is set only when the vm object
lock is released while the vm page is still in transition.  Typically,
this is when it is undergoing I/O.

1 files changed, 0 insertions, 2 deletions

diff --git a/sys/vm/vm_contig.c b/sys/vm/vm_contig.c
index 5ebf1bc..952d26d 100644
--- a/sys/vm/vm_contig.c
+++ b/sys/vm/vm_contig.c
@@ -256,7 +256,6 @@ again1:
 					start++;
 					goto again0;
 				}
-				vm_page_busy(m);
 				vm_page_free(m);
 				VM_OBJECT_UNLOCK(object);
 			}
@@ -459,7 +458,6 @@ cleanup_freed:
 				object = m->object;
 				if (!VM_OBJECT_TRYLOCK(object))
 					goto retry;
-				vm_page_busy(m);
 				vm_page_free(m);
 				VM_OBJECT_UNLOCK(object);
 			}