Use the trick of performing the atomic operation on the contained aligned

word to handle the dirty mask updates in vm_page_clear_dirty_mask().
Remove the vm page queue lock around vm_page_dirty() call in vm_fault_hold()
the sole purpose of which was to protect dirty on architectures which
does not provide short or byte-wide atomics.

Reviewed by:	alc, attilio
Tested by:	flo (sparc64)
MFC after:	2 weeks

1 files changed, 13 insertions, 13 deletions

diff --git a/sys/vm/vm_page.h b/sys/vm/vm_page.h
index f7f3aed..1218dc8 100644
--- a/sys/vm/vm_page.h
+++ b/sys/vm/vm_page.h
@@ -94,21 +94,21 @@
  *	object that the page belongs to (O), the pool lock for the page (P),
  *	or the lock for either the free or paging queues (Q).  If a field is
  *	annotated below with two of these locks, then holding either lock is
- *	sufficient for read access, but both locks are required for write 
+ *	sufficient for read access, but both locks are required for write
  *	access.
  *
- *	In contrast, the synchronization of accesses to the page's dirty field
- *	is machine dependent (M).  In the machine-independent layer, the lock
- *	on the object that the page belongs to must be held in order to
- *	operate on the field.  However, the pmap layer is permitted to set
- *	all bits within the field without holding that lock.  Therefore, if
- *	the underlying architecture does not support atomic read-modify-write
- *	operations on the field's type, then the machine-independent layer
- *	must also hold the page queues lock when performing read-modify-write
- *	operations and the pmap layer must hold the page queues lock when
- *	setting the field.  In the machine-independent layer, the
- *	implementation of read-modify-write operations on the field is
- *	encapsulated in vm_page_clear_dirty_mask().
+ *	In contrast, the synchronization of accesses to the page's
+ *	dirty field is machine dependent (M).  In the
+ *	machine-independent layer, the lock on the object that the
+ *	page belongs to must be held in order to operate on the field.
+ *	However, the pmap layer is permitted to set all bits within
+ *	the field without holding that lock.  If the underlying
+ *	architecture does not support atomic read-modify-write
+ *	operations on the field's type, then the machine-independent
+ *	layer uses 32bit atomic on the aligned 32bit word that
+ *	contains the dirty field.  In the machine-independent layer,
+ *	the implementation of read-modify-write operations on the
+ *	field is encapsulated in vm_page_clear_dirty_mask().
  */
 
 TAILQ_HEAD(pglist, vm_page);