From e3674072596e4a11f628f4e23d1472741e99ca18 Mon Sep 17 00:00:00 2001
From: jeff <jeff@FreeBSD.org>
Date: Tue, 29 Oct 2019 20:46:25 +0000
Subject: [PATCH] Drop the object lock earlier in fault and don't relock it
 after pmap_enter().

Recent changes in object and page locking have enabled more lock pushdown.

Reviewed by:	kib
Tested by:	pho
Differential Revision:	https://reviews.freebsd.org/D22036
---
 sys/vm/vm_fault.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/sys/vm/vm_fault.c b/sys/vm/vm_fault.c
index b8d0924243cc..41facf49bbf4 100644
--- a/sys/vm/vm_fault.c
+++ b/sys/vm/vm_fault.c
@@ -184,11 +184,10 @@ unlock_vp(struct faultstate *fs)
 }
 
 static void
-unlock_and_deallocate(struct faultstate *fs)
+fault_deallocate(struct faultstate *fs)
 {
 
 	vm_object_pip_wakeup(fs->object);
-	VM_OBJECT_WUNLOCK(fs->object);
 	if (fs->object != fs->first_object) {
 		VM_OBJECT_WLOCK(fs->first_object);
 		vm_page_free(fs->first_m);
@@ -201,6 +200,14 @@ unlock_and_deallocate(struct faultstate *fs)
 	unlock_vp(fs);
 }
 
+static void
+unlock_and_deallocate(struct faultstate *fs)
+{
+
+	VM_OBJECT_WUNLOCK(fs->object);
+	fault_deallocate(fs);
+}
+
 static void
 vm_fault_dirty(vm_map_entry_t entry, vm_page_t m, vm_prot_t prot,
     vm_prot_t fault_type, int fault_flags, bool set_wd)
@@ -1261,10 +1268,12 @@ vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
 				    fs.object, OFF_TO_IDX(
 				    fs.first_object->backing_object_offset));
 #endif
+				VM_OBJECT_WUNLOCK(fs.object);
 				fs.first_m = fs.m;
 				fs.m = NULL;
 				VM_CNT_INC(v_cow_optim);
 			} else {
+				VM_OBJECT_WUNLOCK(fs.object);
 				/*
 				 * Oh, well, lets copy it.
 				 */
@@ -1285,7 +1294,6 @@ vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
 			 * conditional
 			 */
 			vm_object_pip_wakeup(fs.object);
-			VM_OBJECT_WUNLOCK(fs.object);
 
 			/*
 			 * We only try to prefault read-only mappings to the
@@ -1405,7 +1413,6 @@ vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
 		vm_fault_prefault(&fs, vaddr,
 		    faultcount > 0 ? behind : PFBAK,
 		    faultcount > 0 ? ahead : PFFOR, false);
-	VM_OBJECT_WLOCK(fs.object);
 
 	/*
 	 * If the page is not wired down, then put it where the pageout daemon
@@ -1427,7 +1434,7 @@ vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
 	/*
 	 * Unlock everything, and return
 	 */
-	unlock_and_deallocate(&fs);
+	fault_deallocate(&fs);
 	if (hardfault) {
 		VM_CNT_INC(v_io_faults);
 		curthread->td_ru.ru_majflt++;