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Tidy up vm_map_simplify_entry() and its recently introduced helper

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functions.  Notably, reflow the text of some comments so that they
occupy fewer lines, and introduce an assertion in one of the new
helper functions so that it is not misused by a future caller.

In collaboration with:	Doug Moore <dougm@rice.edu>
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D17635
This commit is contained in:
Alan Cox 2018-11-18 01:27:17 +00:00
parent 835998c210
commit 92e78c1012
1 changed files with 21 additions and 18 deletions
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39
sys/vm/vm_map.c
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@ -1644,16 +1644,25 @@ vm_map_find_min(vm_map_t map, vm_object_t object, vm_ooffset_t offset,
}
}
/*
* A map entry with any of the following flags set must not be merged with
* another entry.
*/
#define MAP_ENTRY_NOMERGE_MASK (MAP_ENTRY_GROWS_DOWN | MAP_ENTRY_GROWS_UP | \
MAP_ENTRY_IN_TRANSITION | MAP_ENTRY_IS_SUB_MAP)
static bool
vm_map_mergeable_neighbors(vm_map_entry_t prev, vm_map_entry_t entry)
{
vm_size_t prevsize;
prevsize = prev->end - prev->start;
KASSERT((prev->eflags & MAP_ENTRY_NOMERGE_MASK) == 0 ||
(entry->eflags & MAP_ENTRY_NOMERGE_MASK) == 0,
("vm_map_mergeable_neighbors: neither %p nor %p are mergeable",
prev, entry));
return (prev->end == entry->start &&
prev->object.vm_object == entry->object.vm_object &&
(prev->object.vm_object == NULL ||
prev->offset + prevsize == entry->offset) &&
prev->offset + (prev->end - prev->start) == entry->offset) &&
prev->eflags == entry->eflags &&
prev->protection == entry->protection &&
prev->max_protection == entry->max_protection &&
@ -1667,18 +1676,14 @@ vm_map_merged_neighbor_dispose(vm_map_t map, vm_map_entry_t entry)
{
/*
* If the backing object is a vnode object,
* vm_object_deallocate() calls vrele().
* However, vrele() does not lock the vnode
* because the vnode has additional
* references. Thus, the map lock can be kept
* without causing a lock-order reversal with
* the vnode lock.
* If the backing object is a vnode object, vm_object_deallocate()
* calls vrele(). However, vrele() does not lock the vnode because
* the vnode has additional references. Thus, the map lock can be
* kept without causing a lock-order reversal with the vnode lock.
*
* Since we count the number of virtual page
* mappings in object->un_pager.vnp.writemappings,
* the writemappings value should not be adjusted
* when the entry is disposed of.
* Since we count the number of virtual page mappings in
* object->un_pager.vnp.writemappings, the writemappings value
* should not be adjusted when the entry is disposed of.
*/
if (entry->object.vm_object != NULL)
vm_object_deallocate(entry->object.vm_object);
@ -1704,10 +1709,8 @@ vm_map_simplify_entry(vm_map_t map, vm_map_entry_t entry)
{
vm_map_entry_t next, prev;
if ((entry->eflags & (MAP_ENTRY_GROWS_DOWN | MAP_ENTRY_GROWS_UP |
MAP_ENTRY_IN_TRANSITION | MAP_ENTRY_IS_SUB_MAP)) != 0)
if ((entry->eflags & MAP_ENTRY_NOMERGE_MASK) != 0)
return;
prev = entry->prev;
if (vm_map_mergeable_neighbors(prev, entry)) {
vm_map_entry_unlink(map, prev);
@ -1717,7 +1720,6 @@ vm_map_simplify_entry(vm_map_t map, vm_map_entry_t entry)
vm_map_entry_resize_free(map, entry->prev);
vm_map_merged_neighbor_dispose(map, prev);
}
next = entry->next;
if (vm_map_mergeable_neighbors(entry, next)) {
vm_map_entry_unlink(map, next);
@ -1726,6 +1728,7 @@ vm_map_simplify_entry(vm_map_t map, vm_map_entry_t entry)
vm_map_merged_neighbor_dispose(map, next);
}
}
/*
* vm_map_clip_start: [ internal use only ]
*