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Fix a very subtile problem that causes unnessary numbers of objects backing

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a single logical object.
Submitted by:	Alan Cox <alc@cs.rice.edu>
This commit is contained in:
John Dyson 1997-07-27 04:44:12 +00:00
parent 7deb24a6ae
commit 11cccda1de
1 changed files with 48 additions and 17 deletions
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65
sys/vm/vm_map.c
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@ -61,7 +61,7 @@
* any improvements or extensions that they make and grant Carnegie the
* rights to redistribute these changes.
*
* $Id: vm_map.c,v 1.77 1997/06/15 23:33:52 dyson Exp $
* $Id: vm_map.c,v 1.78 1997/06/23 21:51:03 tegge Exp $
*/
/*
@ -936,6 +936,23 @@ _vm_map_clip_start(map, entry, start)
vm_map_simplify_entry(map, entry);
/*
* If there is no object backing this entry, we might as well create
* one now. If we defer it, an object can get created after the map
* is clipped, and individual objects will be created for the split-up
* map. This is a bit of a hack, but is also about the best place to
* put this improvement.
*/
if (entry->object.vm_object == NULL) {
vm_object_t object;
object = vm_object_allocate(OBJT_DEFAULT,
OFF_TO_IDX(entry->end - entry->start));
entry->object.vm_object = object;
entry->offset = 0;
}
new_entry = vm_map_entry_create(map);
*new_entry = *entry;
@ -977,6 +994,23 @@ _vm_map_clip_end(map, entry, end)
{
register vm_map_entry_t new_entry;
/*
* If there is no object backing this entry, we might as well create
* one now. If we defer it, an object can get created after the map
* is clipped, and individual objects will be created for the split-up
* map. This is a bit of a hack, but is also about the best place to
* put this improvement.
*/
if (entry->object.vm_object == NULL) {
vm_object_t object;
object = vm_object_allocate(OBJT_DEFAULT,
OFF_TO_IDX(entry->end - entry->start));
entry->object.vm_object = object;
entry->offset = 0;
}
/*
* Create a new entry and insert it AFTER the specified entry
*/
@ -2148,23 +2182,20 @@ vmspace_fork(vm1)
case VM_INHERIT_NONE:
break;
case VM_INHERIT_SHARE:
/*
* Clone the entry, creating the shared object if necessary.
*/
object = old_entry->object.vm_object;
if (object == NULL) {
object = vm_object_allocate(OBJT_DEFAULT,
OFF_TO_IDX(old_entry->end -
old_entry->start));
old_entry->object.vm_object = object;
old_entry->offset = (vm_offset_t) 0;
} else if (old_entry->eflags & MAP_ENTRY_NEEDS_COPY) {
case VM_INHERIT_SHARE:
/*
* Clone the entry, creating the shared object if necessary.
*/
object = old_entry->object.vm_object;
if (object == NULL) {
object = vm_object_allocate(OBJT_DEFAULT,
OFF_TO_IDX(old_entry->end - old_entry->start));
old_entry->object.vm_object = object;
old_entry->offset = (vm_offset_t) 0;
} else if (old_entry->eflags & MAP_ENTRY_NEEDS_COPY) {
vm_object_shadow(&old_entry->object.vm_object,
&old_entry->offset,
OFF_TO_IDX(old_entry->end -
old_entry->start));
&old_entry->offset,
OFF_TO_IDX(old_entry->end - old_entry->start));
old_entry->eflags &= ~MAP_ENTRY_NEEDS_COPY;
object = old_entry->object.vm_object;
}