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, 8 insertions, 0 deletions

diff --git a/sys/sparc64/sparc64/pmap.c b/sys/sparc64/sparc64/pmap.c
index 18cd0f9..fa964ab 100644
--- a/sys/sparc64/sparc64/pmap.c
+++ b/sys/sparc64/sparc64/pmap.c
@@ -1401,9 +1401,17 @@ vm_page_t
 pmap_enter_quick(pmap_t pm, vm_offset_t va, vm_page_t m, vm_page_t mpte)
 {
 
+	vm_page_lock_queues();
+	vm_page_busy(m);
+	vm_page_unlock_queues();
+	VM_OBJECT_UNLOCK(m->object);
 	mtx_lock(&Giant);
 	pmap_enter(pm, va, m, VM_PROT_READ | VM_PROT_EXECUTE, FALSE);
 	mtx_unlock(&Giant);
+	VM_OBJECT_LOCK(m->object);
+	vm_page_lock_queues();
+	vm_page_wakeup(m);
+	vm_page_unlock_queues();
 	return (NULL);
 }