Add a special page zero entry point intended to be called via the single

threaded VM pagezero kthread outside of Giant.  For some platforms, this
is really easy since it can just use the direct mapped region.  For others,
IPI sending is involved or there are other issues, so grab Giant when
needed.

We still have preemption issues to deal with, but Alan Cox has an
interesting suggestion on how to minimize the problem on x86.

Use Luigi's hack for preserving the (lack of) priority.

Turn the idle zeroing back on since it can now actually do something useful
outside of Giant in many cases.

1 files changed, 9 insertions, 7 deletions

diff --git a/sys/vm/vm_zeroidle.c b/sys/vm/vm_zeroidle.c
index 0552c32..52a055d 100644
--- a/sys/vm/vm_zeroidle.c
+++ b/sys/vm/vm_zeroidle.c
@@ -30,7 +30,7 @@ static int cnt_prezero;
 SYSCTL_INT(_vm_stats_misc, OID_AUTO,
 	cnt_prezero, CTLFLAG_RD, &cnt_prezero, 0, "");
 
-static int idlezero_enable = 0;
+static int idlezero_enable = 1;
 SYSCTL_INT(_vm, OID_AUTO, idlezero_enable, CTLFLAG_RW, &idlezero_enable, 0, "");
 TUNABLE_INT("vm.idlezero_enable", &idlezero_enable);
 
@@ -83,9 +83,9 @@ vm_page_zero_idle(void)
 		TAILQ_REMOVE(&vm_page_queues[m->queue].pl, m, pageq);
 		m->queue = PQ_NONE;
 		mtx_unlock(&vm_page_queue_free_mtx);
-		/* maybe drop out of Giant here */
-		pmap_zero_page(m);
-		/* and return here */
+		mtx_unlock(&Giant);
+		pmap_zero_page_idle(m);
+		mtx_lock(&Giant);
 		mtx_lock(&vm_page_queue_free_mtx);
 		vm_page_flag_set(m, PG_ZERO);
 		m->queue = PQ_FREE + m->pc;
@@ -109,7 +109,7 @@ void
 vm_page_zero_idle_wakeup(void)
 {
 
-	if (vm_page_zero_check())
+	if (idlezero_enable && vm_page_zero_check())
 		wakeup(&zero_state);
 }
 
@@ -119,17 +119,19 @@ vm_pagezero(void)
 	struct thread *td = curthread;
 	struct rtprio rtp;
 	int pages = 0;
+	int pri;
 
 	rtp.prio = RTP_PRIO_MAX;
 	rtp.type = RTP_PRIO_IDLE;
 	mtx_lock_spin(&sched_lock);
 	rtp_to_pri(&rtp, td->td_ksegrp);
+	pri = td->td_priority;
 	mtx_unlock_spin(&sched_lock);
 
 	for (;;) {
 		if (vm_page_zero_check()) {
 			pages += vm_page_zero_idle();
-			if (pages > idlezero_maxrun) {
+			if (pages > idlezero_maxrun || kserunnable()) {
 				mtx_lock_spin(&sched_lock);
 				td->td_proc->p_stats->p_ru.ru_nvcsw++;
 				mi_switch();
@@ -137,7 +139,7 @@ vm_pagezero(void)
 				pages = 0;
 			}
 		} else {
-			tsleep(&zero_state, PPAUSE, "pgzero", hz * 300);
+			tsleep(&zero_state, pri, "pgzero", hz * 300);
 			pages = 0;
 		}
 	}