[RFC PATCH 6/7] vm: Add vm_map_coalesce_entry

[Sergey Bugaev]

This function attempts to coalesce a VM map entry with its preceeding
entry. It wraps vm_object_coalesce.
---
 vm/vm_map.c | 77 +++++++++++++++++++++++++++++++++++++++++++++++++++--
 vm/vm_map.h |  2 ++
 2 files changed, 77 insertions(+), 2 deletions(-)

diff --git a/vm/vm_map.c b/vm/vm_map.c
index 97fc09ce..fc7c4381 100644
--- a/vm/vm_map.c
+++ b/vm/vm_map.c
@@ -113,8 +113,7 @@ MACRO_END
  *     start or end value.]  Note that these clippings may not
  *     always be necessary (as the two resulting entries are then
  *     not changed); however, the clipping is done for convenience.
- *     No attempt is currently made to "glue back together" two
- *     abutting entries.
+ *     The entries can later be "glued back together" (coalesced).
  *
  *     The symmetric (shadow) copy strategy implements virtual copy
  *     by copying VM object references from one map to
@@ -4929,6 +4928,80 @@ vm_region_create_proxy (task_t task, vm_address_t 
address,
   return ret;
 }
 
+/*
+ *     Routine:        vm_map_coalesce_entry
+ *     Purpose:
+ *             Try to coalesce an entry with the preceeding entry in the map.
+ *     Conditions:
+ *             The map is locked.  If coalesced, the entry is destroyed
+ *             by the call.
+ *     Returns:
+ *             Whether the entry was coalesced.
+ */
+boolean_t
+vm_map_coalesce_entry(
+       vm_map_t        map,
+       vm_map_entry_t  entry)
+{
+       vm_map_entry_t  prev = entry->vme_prev;
+       vm_size_t       prev_size;
+       vm_size_t       entry_size;
+
+       /*
+        *      Check the basic conditions for coalescing the two entries.
+        */
+       if ((entry == vm_map_to_entry(map)) ||
+           (prev == vm_map_to_entry(map)) ||
+           (prev->vme_end != entry->vme_start) ||
+           (prev->is_shared || entry->is_shared) ||
+           (prev->is_sub_map || entry->is_sub_map) ||
+           (prev->inheritance != entry->inheritance) ||
+           (prev->protection != entry->protection) ||
+           (prev->max_protection != entry->max_protection) ||
+           (prev->needs_copy != entry->needs_copy) ||
+           (prev->in_transition || entry->in_transition) ||
+           (prev->wired_count != entry->wired_count) ||
+           (prev->projected_on != 0) ||
+           (entry->projected_on != 0))
+               return FALSE;
+
+       prev_size = prev->vme_end - prev->vme_start;
+       entry_size = entry->vme_end - entry->vme_start;
+       assert(prev->gap_size == 0);
+
+       /*
+        *      See if we can coalesce the two objects.
+        */
+       if (!vm_object_coalesce(prev->object.vm_object,
+               entry->object.vm_object,
+               prev->offset,
+               entry->offset,
+               prev_size,
+               entry_size))
+               return FALSE;
+
+       /*
+        *      Update the hints.
+        */
+       if (map->hint == entry)
+               SAVE_HINT(map, prev);
+       if (map->first_free == entry)
+               map->first_free = prev;
+
+       /*
+        *      Get rid of the entry without changing any wirings or the pmap,
+       *       and without altering map->size.
+        */
+       prev->vme_end = entry->vme_end;
+       vm_map_entry_unlink(map, entry);
+       vm_object_deallocate(entry->object.vm_object);
+       vm_map_entry_dispose(map, entry);
+
+       return TRUE;
+}
+
+
+
 /*
  *     Routine:        vm_map_machine_attribute
  *     Purpose:
diff --git a/vm/vm_map.h b/vm/vm_map.h
index 3d1c9428..a4949e4e 100644
--- a/vm/vm_map.h
+++ b/vm/vm_map.h
@@ -442,6 +442,8 @@ extern vm_map_copy_t        vm_map_copy_copy(vm_map_copy_t);
 extern kern_return_t   vm_map_copy_discard_cont(vm_map_copyin_args_t,
                                                 vm_map_copy_t *);
 
+extern boolean_t       vm_map_coalesce_entry(vm_map_t, vm_map_entry_t);
+
 /* Add or remove machine- dependent attributes from map regions */
 extern kern_return_t   vm_map_machine_attribute(vm_map_t, vm_offset_t,
                                                 vm_size_t,
-- 
2.41.0