In the common case, pmap_enter_quick() completes without sleeping.

In such cases, the busying of the page and the unlocking of the
containing object by vm_map_pmap_enter() and vm_fault_prefault() is
unnecessary overhead.  To eliminate this overhead, this change
modifies pmap_enter_quick() so that it expects the object to be locked
on entry and it assumes the responsibility for busying the page and
unlocking the object if it must sleep.  Note: alpha, amd64, i386 and
ia64 are the only implementations optimized by this change; arm,
powerpc, and sparc64 still conservatively busy the page and unlock the
object within every pmap_enter_quick() call.

Additionally, this change is the first case where we synchronize
access to the page's PG_BUSY flag and busy field using the containing
object's lock rather than the global page queues lock.  (Modifications
to the page's PG_BUSY flag and busy field have asserted both locks for
several weeks, enabling an incremental transition.)

1 files changed, 4 insertions, 0 deletions

diff --git a/sys/ia64/ia64/pmap.c b/sys/ia64/ia64/pmap.c
index da1bcf1..a2feed7 100644
--- a/sys/ia64/ia64/pmap.c
+++ b/sys/ia64/ia64/pmap.c
@@ -1631,9 +1631,13 @@ pmap_enter_quick(pmap_t pmap, vm_offset_t va, vm_page_t m, vm_page_t mpte)
 	while ((pte = pmap_find_pte(va)) == NULL) {
 		pmap_install(oldpmap);
 		PMAP_UNLOCK(pmap);
+		vm_page_busy(m);
 		vm_page_unlock_queues();
+		VM_OBJECT_UNLOCK(m->object);
 		VM_WAIT;
+		VM_OBJECT_LOCK(m->object);
 		vm_page_lock_queues();
+		vm_page_wakeup(m);
 		PMAP_LOCK(pmap);
 		oldpmap = pmap_install(pmap);
 	}