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Slightly optimize locking in vm_map_copy_swap_entry(). Anonymous objects

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require the object lock to synchronize collapse.  Other swap objects such
as tmpfs do not.

Reported by:	mjg
Reviewed by:	kib, markj
Differential Revision:	https://reviews.freebsd.org/D22747
This commit is contained in:
Jeff Roberson 2019-12-15 02:02:27 +00:00
parent af00971419
commit d966c7615f
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=355764
1 changed files with 12 additions and 9 deletions
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21
sys/vm/vm_map.c
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@ -3870,15 +3870,19 @@ vm_map_copy_swap_object(vm_map_entry_t src_entry, vm_map_entry_t dst_entry,
int charged;
src_object = src_entry->object.vm_object;
VM_OBJECT_WLOCK(src_object);
charged = ENTRY_CHARGED(src_entry);
vm_object_collapse(src_object);
if ((src_object->flags & OBJ_ONEMAPPING) != 0) {
vm_object_split(src_entry);
src_object = src_entry->object.vm_object;
}
vm_object_reference_locked(src_object);
vm_object_clear_flag(src_object, OBJ_ONEMAPPING);
if ((src_object->flags & OBJ_ANON) != 0) {
VM_OBJECT_WLOCK(src_object);
vm_object_collapse(src_object);
if ((src_object->flags & OBJ_ONEMAPPING) != 0) {
vm_object_split(src_entry);
src_object = src_entry->object.vm_object;
}
vm_object_reference_locked(src_object);
vm_object_clear_flag(src_object, OBJ_ONEMAPPING);
VM_OBJECT_WUNLOCK(src_object);
} else
vm_object_reference(src_object);
if (src_entry->cred != NULL &&
!(src_entry->eflags & MAP_ENTRY_NEEDS_COPY)) {
KASSERT(src_object->cred == NULL,
@ -3887,7 +3891,6 @@ vm_map_copy_swap_object(vm_map_entry_t src_entry, vm_map_entry_t dst_entry,
src_object->cred = src_entry->cred;
src_object->charge = size;
}
VM_OBJECT_WUNLOCK(src_object);
dst_entry->object.vm_object = src_object;
if (charged) {
cred = curthread->td_ucred;