From 7d737c65b5d787406b2d2c8983065394c52b68d3 Mon Sep 17 00:00:00 2001 From: alc Date: Sat, 25 Feb 2012 17:49:59 +0000 Subject: [PATCH] Simplify vmspace_fork()'s control flow by copying immutable data before the vm map locks are acquired. Also, eliminate redundant initialization of the new vm map's timestamp. Reviewed by: kib MFC after: 3 weeks --- sys/vm/vm_map.c | 24 ++++++++++-------------- 1 file changed, 10 insertions(+), 14 deletions(-) diff --git a/sys/vm/vm_map.c b/sys/vm/vm_map.c index 7d228cb1eab1..6484a9fd0392 100644 --- a/sys/vm/vm_map.c +++ b/sys/vm/vm_map.c @@ -3082,27 +3082,25 @@ struct vmspace * vmspace_fork(struct vmspace *vm1, vm_ooffset_t *fork_charge) { struct vmspace *vm2; - vm_map_t old_map = &vm1->vm_map; - vm_map_t new_map; - vm_map_entry_t old_entry; - vm_map_entry_t new_entry; + vm_map_t new_map, old_map; + vm_map_entry_t new_entry, old_entry; vm_object_t object; int locked; - vm_map_lock(old_map); - if (old_map->busy) - vm_map_wait_busy(old_map); - new_map = NULL; /* silence gcc */ + old_map = &vm1->vm_map; + /* Copy immutable fields of vm1 to vm2. */ vm2 = vmspace_alloc(old_map->min_offset, old_map->max_offset); if (vm2 == NULL) - goto unlock_and_return; + return (NULL); vm2->vm_taddr = vm1->vm_taddr; vm2->vm_daddr = vm1->vm_daddr; vm2->vm_maxsaddr = vm1->vm_maxsaddr; - new_map = &vm2->vm_map; /* XXX */ + vm_map_lock(old_map); + if (old_map->busy) + vm_map_wait_busy(old_map); + new_map = &vm2->vm_map; locked = vm_map_trylock(new_map); /* trylock to silence WITNESS */ KASSERT(locked, ("vmspace_fork: lock failed")); - new_map->timestamp = 1; old_entry = old_map->header.next; @@ -3223,15 +3221,13 @@ vmspace_fork(struct vmspace *vm1, vm_ooffset_t *fork_charge) } old_entry = old_entry->next; } -unlock_and_return: /* * Use inlined vm_map_unlock() to postpone handling the deferred * map entries, which cannot be done until both old_map and * new_map locks are released. */ sx_xunlock(&old_map->lock); - if (vm2 != NULL) - sx_xunlock(&new_map->lock); + sx_xunlock(&new_map->lock); vm_map_process_deferred(); return (vm2);