[src/trunk]: src/sys/uvm Modify uvm_map_pageable() and uvm_map_pageable_all()...

[thorpej <thorpej%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/67c3c74cd58b
branches:  trunk
changeset: 473715:67c3c74cd58b
user:      thorpej <thorpej%NetBSD.org@localhost>
date:      Wed Jun 16 19:34:24 1999 +0000

description:
Modify uvm_map_pageable() and uvm_map_pageable_all() to follow POSIX 1003.1b
semantics.  That is, regardless of the number of mlock/mlockall calls,
an munlock/munlockall actually unlocks the region (i.e. sets wiring count
to 0).

Add a comment describing why uvm_map_pageable() should not be used for
transient page wirings (e.g. for physio) -- note, it's currently only
(ab)used in this way by a few pieces of code which are known to be
broken, i.e. the Amiga and Atari pmaps, and i386 and pc532 if PMAP_NEW is
not used.  The i386 GDT code uses uvm_map_pageable(), but in a safe
way, and could be trivially converted to use uvm_fault_wire() instead.

diffstat:

 sys/uvm/uvm_map.c |  35 +++++++++++++++--------------------
 1 files changed, 15 insertions(+), 20 deletions(-)

diffs (107 lines):

diff -r d2e52e0660d7 -r 67c3c74cd58b sys/uvm/uvm_map.c
--- a/sys/uvm/uvm_map.c Wed Jun 16 18:43:28 1999 +0000
+++ b/sys/uvm/uvm_map.c Wed Jun 16 19:34:24 1999 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: uvm_map.c,v 1.55 1999/06/16 00:29:04 thorpej Exp $     */
+/*     $NetBSD: uvm_map.c,v 1.56 1999/06/16 19:34:24 thorpej Exp $     */
 
 /* 
  * Copyright (c) 1997 Charles D. Cranor and Washington University.
@@ -599,7 +599,7 @@
                    prev_entry->advice != advice)
                        goto step3;
 
-               /* wired_count's must match (new area is unwired) */
+               /* wiring status must match (new area is unwired) */
                if (VM_MAPENT_ISWIRED(prev_entry))
                        goto step3; 
 
@@ -1978,6 +1978,8 @@
 /*
  * uvm_map_pageable: sets the pageability of a range in a map.
  *
+ * => wires map entries.  should not be used for transient page locking.
+ *     for that, use uvm_fault_wire()/uvm_fault_unwire() (see uvm_vslock()).
  * => regions sepcified as not pageable require lock-down (wired) memory
  *     and page tables.
  * => map must not be locked.
@@ -2024,10 +2026,8 @@
         * handle wiring and unwiring seperately.
         */
 
-       if (new_pageable) {                     /* unwire */
-
+       if (new_pageable) {             /* unwire */
                UVM_MAP_CLIP_START(map, entry, start);
-
                /*
                 * unwiring.  first ensure that the range to be unwired is
                 * really wired down and that there are no holes.  
@@ -2046,20 +2046,18 @@
                }
 
                /* 
-                * now decrement the wiring count for each region.  if a region
-                * becomes completely unwired, unwire its physical pages and
-                * mappings.
+                * POSIX 1003.1b - a single munlock call unlocks a region,
+                * regardless of the number of mlock calls made on that
+                * region.
                 *
                 * Note, uvm_fault_unwire() (called via uvm_map_entry_unwire())
                 * does not lock the map, so we don't have to do anything
                 * special regarding locking here.
                 */
-
                entry = start_entry;
                while ((entry != &map->header) && (entry->start < end)) {
                        UVM_MAP_CLIP_END(map, entry, end);
-                       entry->wired_count--;
-                       if (VM_MAPENT_ISWIRED(entry) == 0)
+                       if (VM_MAPENT_ISWIRED(entry))
                                uvm_map_entry_unwire(map, entry);
                        entry = entry->next;
                }
@@ -2080,7 +2078,7 @@
         *    be wired and increment its wiring count.  
         *
         * 2: we downgrade to a read lock, and call uvm_fault_wire to fault
-        *    in the pages for any newly wired area (wired_count is 1).
+        *    in the pages for any newly wired area (wired_count == 1).
         *
         *    downgrading to a read lock for uvm_fault_wire avoids a possible
         *    deadlock with another thread that may have faulted on one of
@@ -2235,8 +2233,8 @@
 
        if (flags == 0) {                       /* unwire */
                /*
-                * Decrement the wiring count on the entries.  If they
-                * reach zero, unwire them.
+                * POSIX 1003.1b -- munlockall unlocks all regions,
+                * regardless of how many times mlockall has been called.
                 *
                 * Note, uvm_fault_unwire() (called via uvm_map_entry_unwire())
                 * does not lock the map, so we don't have to do anything
@@ -2244,11 +2242,8 @@
                 */
                for (entry = map->header.next; entry != &map->header;
                     entry = entry->next) {
-                       if (VM_MAPENT_ISWIRED(entry)) {
-                               entry->wired_count--;
-                               if (VM_MAPENT_ISWIRED(entry) == 0)
-                                       uvm_map_entry_unwire(map, entry);
-                       }
+                       if (VM_MAPENT_ISWIRED(entry))
+                               uvm_map_entry_unwire(map, entry);
                }
                map->flags &= ~VM_MAP_WIREFUTURE;
                vm_map_unlock(map);
@@ -2286,7 +2281,7 @@
         *    need to be created.  then we increment its wiring count.
         *
         * 3: we downgrade to a read lock, and call uvm_fault_wire to fault
-        *    in the pages for any newly wired area (wired count is 1).
+        *    in the pages for any newly wired area (wired_count == 1).
         *
         *    downgrading to a read lock for uvm_fault_wire avoids a possible
         *    deadlock with another thread that may have faulted on one of