Author: alc
Date: Sat Feb 25 17:49:59 2012
New Revision: 232160
URL: http://svn.freebsd.org/changeset/base/232160
Log:
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
Modified:
head/sys/vm/vm_map.c
Modified: head/sys/vm/vm_map.c
==============================================================================
--- head/sys/vm/vm_map.c Sat Feb 25 16:02:12 2012 (r232159)
+++ head/sys/vm/vm_map.c Sat Feb 25 17:49:59 2012 (r232160)
@@ -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_oof
}
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);
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