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Initialize the eflags field of vm_map headers.

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Initializing the eflags field of the map->header entry to a value with a
unique new bit set makes a few comparisons to &map->header unnecessary.

Submitted by:	Doug Moore <dougm@rice.edu>
Reviewed by:	alc, kib
Tested by:	pho
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D14005
This commit is contained in:
Mark Johnston 2018-11-02 16:26:44 +00:00
parent 5c239d80c0
commit 2203c46d87
3 changed files with 17 additions and 18 deletions
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5
sys/kern/sys_process.c
View File

@ -387,8 +387,9 @@ ptrace_vm_entry(struct thread *td, struct proc *p, struct ptrace_vm_entry *pve)
error = EINVAL;
break;
}
while (entry != &map->header &&
(entry->eflags & MAP_ENTRY_IS_SUB_MAP) != 0) {
KASSERT((map->header.eflags & MAP_ENTRY_IS_SUB_MAP) == 0,
("Submap in map header"));
while ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) != 0) {
entry = entry->next;
index++;
}

11
sys/vm/vm_map.c
View File

@ -796,6 +796,7 @@ _vm_map_init(vm_map_t map, pmap_t pmap, vm_offset_t min, vm_offset_t max)
{
map->header.next = map->header.prev = &map->header;
map->header.eflags = MAP_ENTRY_HEADER;
map->needs_wakeup = FALSE;
map->system_map = 0;
map->pmap = pmap;
@ -1277,8 +1278,8 @@ vm_map_insert(vm_map_t map, vm_object_t object, vm_ooffset_t offset,
if (object->ref_count > 1 || object->shadow_count != 0)
vm_object_clear_flag(object, OBJ_ONEMAPPING);
VM_OBJECT_WUNLOCK(object);
} else if (prev_entry != &map->header &&
(prev_entry->eflags & ~MAP_ENTRY_USER_WIRED) == protoeflags &&
} else if ((prev_entry->eflags & ~MAP_ENTRY_USER_WIRED) ==
protoeflags &&
(cow & (MAP_STACK_GROWS_DOWN | MAP_STACK_GROWS_UP)) == 0 &&
prev_entry->end == start && (prev_entry->cred == cred ||
(prev_entry->object.vm_object != NULL &&
@ -1708,8 +1709,7 @@ vm_map_simplify_entry(vm_map_t map, vm_map_entry_t entry)
return;
prev = entry->prev;
if (prev != &map->header &&
vm_map_mergeable_neighbors(prev, entry)) {
if (vm_map_mergeable_neighbors(prev, entry)) {
vm_map_entry_unlink(map, prev);
entry->start = prev->start;
entry->offset = prev->offset;
@ -1719,8 +1719,7 @@ vm_map_simplify_entry(vm_map_t map, vm_map_entry_t entry)
}
next = entry->next;
if (next != &map->header &&
vm_map_mergeable_neighbors(entry, next)) {
if (vm_map_mergeable_neighbors(entry, next)) {
vm_map_entry_unlink(map, next);
entry->end = next->end;
vm_map_entry_resize_free(map, entry);

19
sys/vm/vm_map.h
View File

@ -146,6 +146,7 @@ struct vm_map_entry {
#define MAP_ENTRY_GUARD 0x10000
#define MAP_ENTRY_STACK_GAP_DN 0x20000
#define MAP_ENTRY_STACK_GAP_UP 0x40000
#define MAP_ENTRY_HEADER 0x80000
#ifdef _KERNEL
static __inline u_char
@ -175,24 +176,22 @@ vm_map_entry_system_wired_count(vm_map_entry_t entry)
* list. Both structures are ordered based upon the start and
* end addresses contained within each map entry.
*
* Counterintuitively, the map's min offset value is stored in
* map->header.end, and its max offset value is stored in
* map->header.start.
*
* The list header has max start value and min end value to act
* as sentinels for sequential search of the doubly-linked list.
* Sleator and Tarjan's top-down splay algorithm is employed to
* control height imbalance in the binary search tree.
*
* The map's min offset value is stored in map->header.end, and
* its max offset value is stored in map->header.start. These
* values act as sentinels for any forward or backward address
* scan of the list. The map header has a special value for the
* eflags field, MAP_ENTRY_HEADER, that is set initially, is
* never changed, and prevents an eflags match of the header
* with any other map entry.
*
* List of locks
* (c) const until freed
*/
struct vm_map {
struct vm_map_entry header; /* List of entries */
/*
map min_offset header.end (c)
map max_offset header.start (c)
*/
struct sx lock; /* Lock for map data */
struct mtx system_mtx;
int nentries; /* Number of entries */