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/kern/kern_subr.c b/sys/kern/kern_subr.c
index cf09244..1d55b44 100644
--- a/sys/kern/kern_subr.c
+++ b/sys/kern/kern_subr.c
@@ -97,7 +97,6 @@ vm_pgmoveco(vm_map_t mapa, vm_object_t srcobj, vm_offset_t kaddr,
 		do
 			vm_page_lock_queues();
 		while (vm_page_sleep_if_busy(user_pg, 1, "vm_pgmoveco"));
-		vm_page_busy(user_pg);
 		pmap_remove_all(user_pg);
 		vm_page_free(user_pg);
 	} else
@@ -114,7 +113,6 @@ vm_pgmoveco(vm_map_t mapa, vm_object_t srcobj, vm_offset_t kaddr,
 			panic("vm_pgmoveco: renaming busy page");
 	}
 	kpindex = kern_pg->pindex;
-	vm_page_busy(kern_pg);
 	vm_page_rename(kern_pg, uobject, upindex);
 	vm_page_flag_clear(kern_pg, PG_BUSY);
 	kern_pg->valid = VM_PAGE_BITS_ALL;