kernel - Introduce lightweight buffers
[dragonfly.git] / sys / vm / vm_fault.c
1 /*
2  * Copyright (c) 1991, 1993
3  *      The Regents of the University of California.  All rights reserved.
4  * Copyright (c) 1994 John S. Dyson
5  * All rights reserved.
6  * Copyright (c) 1994 David Greenman
7  * All rights reserved.
8  *
9  *
10  * This code is derived from software contributed to Berkeley by
11  * The Mach Operating System project at Carnegie-Mellon University.
12  *
13  * Redistribution and use in source and binary forms, with or without
14  * modification, are permitted provided that the following conditions
15  * are met:
16  * 1. Redistributions of source code must retain the above copyright
17  *    notice, this list of conditions and the following disclaimer.
18  * 2. Redistributions in binary form must reproduce the above copyright
19  *    notice, this list of conditions and the following disclaimer in the
20  *    documentation and/or other materials provided with the distribution.
21  * 3. All advertising materials mentioning features or use of this software
22  *    must display the following acknowledgement:
23  *      This product includes software developed by the University of
24  *      California, Berkeley and its contributors.
25  * 4. Neither the name of the University nor the names of its contributors
26  *    may be used to endorse or promote products derived from this software
27  *    without specific prior written permission.
28  *
29  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
30  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
31  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
32  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
33  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
34  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
35  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
36  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
37  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
38  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
39  * SUCH DAMAGE.
40  *
41  *      from: @(#)vm_fault.c    8.4 (Berkeley) 1/12/94
42  *
43  *
44  * Copyright (c) 1987, 1990 Carnegie-Mellon University.
45  * All rights reserved.
46  *
47  * Authors: Avadis Tevanian, Jr., Michael Wayne Young
48  *
49  * Permission to use, copy, modify and distribute this software and
50  * its documentation is hereby granted, provided that both the copyright
51  * notice and this permission notice appear in all copies of the
52  * software, derivative works or modified versions, and any portions
53  * thereof, and that both notices appear in supporting documentation.
54  *
55  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
56  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
57  * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
58  *
59  * Carnegie Mellon requests users of this software to return to
60  *
61  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
62  *  School of Computer Science
63  *  Carnegie Mellon University
64  *  Pittsburgh PA 15213-3890
65  *
66  * any improvements or extensions that they make and grant Carnegie the
67  * rights to redistribute these changes.
68  *
69  * $FreeBSD: src/sys/vm/vm_fault.c,v 1.108.2.8 2002/02/26 05:49:27 silby Exp $
70  * $DragonFly: src/sys/vm/vm_fault.c,v 1.47 2008/07/01 02:02:56 dillon Exp $
71  */
72
73 /*
74  *      Page fault handling module.
75  */
76
77 #include <sys/param.h>
78 #include <sys/systm.h>
79 #include <sys/kernel.h>
80 #include <sys/proc.h>
81 #include <sys/vnode.h>
82 #include <sys/resourcevar.h>
83 #include <sys/vmmeter.h>
84 #include <sys/vkernel.h>
85 #include <sys/lock.h>
86 #include <sys/sysctl.h>
87
88 #include <cpu/lwbuf.h>
89
90 #include <vm/vm.h>
91 #include <vm/vm_param.h>
92 #include <vm/pmap.h>
93 #include <vm/vm_map.h>
94 #include <vm/vm_object.h>
95 #include <vm/vm_page.h>
96 #include <vm/vm_pageout.h>
97 #include <vm/vm_kern.h>
98 #include <vm/vm_pager.h>
99 #include <vm/vnode_pager.h>
100 #include <vm/vm_extern.h>
101
102 #include <sys/thread2.h>
103 #include <vm/vm_page2.h>
104
105 struct faultstate {
106         vm_page_t m;
107         vm_object_t object;
108         vm_pindex_t pindex;
109         vm_prot_t prot;
110         vm_page_t first_m;
111         vm_object_t first_object;
112         vm_prot_t first_prot;
113         vm_map_t map;
114         vm_map_entry_t entry;
115         int lookup_still_valid;
116         int didlimit;
117         int hardfault;
118         int fault_flags;
119         int map_generation;
120         boolean_t wired;
121         struct vnode *vp;
122 };
123
124 static int vm_fast_fault = 1;
125 SYSCTL_INT(_vm, OID_AUTO, fast_fault, CTLFLAG_RW, &vm_fast_fault, 0, "");
126 static int debug_cluster = 0;
127 SYSCTL_INT(_vm, OID_AUTO, debug_cluster, CTLFLAG_RW, &debug_cluster, 0, "");
128
129 static int vm_fault_object(struct faultstate *, vm_pindex_t, vm_prot_t);
130 static int vm_fault_vpagetable(struct faultstate *, vm_pindex_t *, vpte_t, int);
131 #if 0
132 static int vm_fault_additional_pages (vm_page_t, int, int, vm_page_t *, int *);
133 #endif
134 static int vm_fault_ratelimit(struct vmspace *);
135 static void vm_prefault(pmap_t pmap, vm_offset_t addra, vm_map_entry_t entry,
136                         int prot);
137
138 static __inline void
139 release_page(struct faultstate *fs)
140 {
141         vm_page_deactivate(fs->m);
142         vm_page_wakeup(fs->m);
143         fs->m = NULL;
144 }
145
146 static __inline void
147 unlock_map(struct faultstate *fs)
148 {
149         if (fs->lookup_still_valid && fs->map) {
150                 vm_map_lookup_done(fs->map, fs->entry, 0);
151                 fs->lookup_still_valid = FALSE;
152         }
153 }
154
155 /*
156  * Clean up after a successful call to vm_fault_object() so another call
157  * to vm_fault_object() can be made.
158  */
159 static void
160 _cleanup_successful_fault(struct faultstate *fs, int relock)
161 {
162         if (fs->object != fs->first_object) {
163                 vm_page_free(fs->first_m);
164                 vm_object_pip_wakeup(fs->object);
165                 fs->first_m = NULL;
166         }
167         fs->object = fs->first_object;
168         if (relock && fs->lookup_still_valid == FALSE) {
169                 if (fs->map)
170                         vm_map_lock_read(fs->map);
171                 fs->lookup_still_valid = TRUE;
172         }
173 }
174
175 static void
176 _unlock_things(struct faultstate *fs, int dealloc)
177 {
178         vm_object_pip_wakeup(fs->first_object);
179         _cleanup_successful_fault(fs, 0);
180         if (dealloc) {
181                 vm_object_deallocate(fs->first_object);
182                 fs->first_object = NULL;
183         }
184         unlock_map(fs); 
185         if (fs->vp != NULL) { 
186                 vput(fs->vp);
187                 fs->vp = NULL;
188         }
189 }
190
191 #define unlock_things(fs) _unlock_things(fs, 0)
192 #define unlock_and_deallocate(fs) _unlock_things(fs, 1)
193 #define cleanup_successful_fault(fs) _cleanup_successful_fault(fs, 1)
194
195 /*
196  * TRYPAGER 
197  *
198  * Determine if the pager for the current object *might* contain the page.
199  *
200  * We only need to try the pager if this is not a default object (default
201  * objects are zero-fill and have no real pager), and if we are not taking
202  * a wiring fault or if the FS entry is wired.
203  */
204 #define TRYPAGER(fs)    \
205                 (fs->object->type != OBJT_DEFAULT && \
206                 (((fs->fault_flags & VM_FAULT_WIRE_MASK) == 0) || fs->wired))
207
208 /*
209  * vm_fault:
210  *
211  * Handle a page fault occuring at the given address, requiring the given
212  * permissions, in the map specified.  If successful, the page is inserted
213  * into the associated physical map.
214  *
215  * NOTE: The given address should be truncated to the proper page address.
216  *
217  * KERN_SUCCESS is returned if the page fault is handled; otherwise,
218  * a standard error specifying why the fault is fatal is returned.
219  *
220  * The map in question must be referenced, and remains so.
221  * The caller may hold no locks.
222  */
223 int
224 vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type, int fault_flags)
225 {
226         int result;
227         vm_pindex_t first_pindex;
228         struct faultstate fs;
229         int growstack;
230
231         mycpu->gd_cnt.v_vm_faults++;
232
233         fs.didlimit = 0;
234         fs.hardfault = 0;
235         fs.fault_flags = fault_flags;
236         growstack = 1;
237
238 RetryFault:
239         /*
240          * Find the vm_map_entry representing the backing store and resolve
241          * the top level object and page index.  This may have the side
242          * effect of executing a copy-on-write on the map entry and/or
243          * creating a shadow object, but will not COW any actual VM pages.
244          *
245          * On success fs.map is left read-locked and various other fields 
246          * are initialized but not otherwise referenced or locked.
247          *
248          * NOTE!  vm_map_lookup will try to upgrade the fault_type to
249          * VM_FAULT_WRITE if the map entry is a virtual page table and also
250          * writable, so we can set the 'A'accessed bit in the virtual page
251          * table entry.
252          */
253         fs.map = map;
254         result = vm_map_lookup(&fs.map, vaddr, fault_type,
255                                &fs.entry, &fs.first_object,
256                                &first_pindex, &fs.first_prot, &fs.wired);
257
258         /*
259          * If the lookup failed or the map protections are incompatible,
260          * the fault generally fails.  However, if the caller is trying
261          * to do a user wiring we have more work to do.
262          */
263         if (result != KERN_SUCCESS) {
264                 if (result != KERN_PROTECTION_FAILURE ||
265                     (fs.fault_flags & VM_FAULT_WIRE_MASK) != VM_FAULT_USER_WIRE)
266                 {
267                         if (result == KERN_INVALID_ADDRESS && growstack &&
268                             map != &kernel_map && curproc != NULL) {
269                                 result = vm_map_growstack(curproc, vaddr);
270                                 if (result != KERN_SUCCESS)
271                                         return (KERN_FAILURE);
272                                 growstack = 0;
273                                 goto RetryFault;
274                         }
275                         return (result);
276                 }
277
278                 /*
279                  * If we are user-wiring a r/w segment, and it is COW, then
280                  * we need to do the COW operation.  Note that we don't
281                  * currently COW RO sections now, because it is NOT desirable
282                  * to COW .text.  We simply keep .text from ever being COW'ed
283                  * and take the heat that one cannot debug wired .text sections.
284                  */
285                 result = vm_map_lookup(&fs.map, vaddr,
286                                        VM_PROT_READ|VM_PROT_WRITE|
287                                         VM_PROT_OVERRIDE_WRITE,
288                                        &fs.entry, &fs.first_object,
289                                        &first_pindex, &fs.first_prot,
290                                        &fs.wired);
291                 if (result != KERN_SUCCESS)
292                         return result;
293
294                 /*
295                  * If we don't COW now, on a user wire, the user will never
296                  * be able to write to the mapping.  If we don't make this
297                  * restriction, the bookkeeping would be nearly impossible.
298                  */
299                 if ((fs.entry->protection & VM_PROT_WRITE) == 0)
300                         fs.entry->max_protection &= ~VM_PROT_WRITE;
301         }
302
303         /*
304          * fs.map is read-locked
305          *
306          * Misc checks.  Save the map generation number to detect races.
307          */
308         fs.map_generation = fs.map->timestamp;
309
310         if (fs.entry->eflags & MAP_ENTRY_NOFAULT) {
311                 panic("vm_fault: fault on nofault entry, addr: %lx",
312                     (u_long)vaddr);
313         }
314
315         /*
316          * A system map entry may return a NULL object.  No object means
317          * no pager means an unrecoverable kernel fault.
318          */
319         if (fs.first_object == NULL) {
320                 panic("vm_fault: unrecoverable fault at %p in entry %p",
321                         (void *)vaddr, fs.entry);
322         }
323
324         /*
325          * Make a reference to this object to prevent its disposal while we
326          * are messing with it.  Once we have the reference, the map is free
327          * to be diddled.  Since objects reference their shadows (and copies),
328          * they will stay around as well.
329          *
330          * Bump the paging-in-progress count to prevent size changes (e.g.
331          * truncation operations) during I/O.  This must be done after
332          * obtaining the vnode lock in order to avoid possible deadlocks.
333          */
334         vm_object_reference(fs.first_object);
335         fs.vp = vnode_pager_lock(fs.first_object);
336         vm_object_pip_add(fs.first_object, 1);
337
338         fs.lookup_still_valid = TRUE;
339         fs.first_m = NULL;
340         fs.object = fs.first_object;    /* so unlock_and_deallocate works */
341
342         /*
343          * If the entry is wired we cannot change the page protection.
344          */
345         if (fs.wired)
346                 fault_type = fs.first_prot;
347
348         /*
349          * The page we want is at (first_object, first_pindex), but if the
350          * vm_map_entry is VM_MAPTYPE_VPAGETABLE we have to traverse the
351          * page table to figure out the actual pindex.
352          *
353          * NOTE!  DEVELOPMENT IN PROGRESS, THIS IS AN INITIAL IMPLEMENTATION
354          * ONLY
355          */
356         if (fs.entry->maptype == VM_MAPTYPE_VPAGETABLE) {
357                 result = vm_fault_vpagetable(&fs, &first_pindex,
358                                              fs.entry->aux.master_pde,
359                                              fault_type);
360                 if (result == KERN_TRY_AGAIN)
361                         goto RetryFault;
362                 if (result != KERN_SUCCESS)
363                         return (result);
364         }
365
366         /*
367          * Now we have the actual (object, pindex), fault in the page.  If
368          * vm_fault_object() fails it will unlock and deallocate the FS
369          * data.   If it succeeds everything remains locked and fs->object
370          * will have an additinal PIP count if it is not equal to
371          * fs->first_object
372          *
373          * vm_fault_object will set fs->prot for the pmap operation.  It is
374          * allowed to set VM_PROT_WRITE if fault_type == VM_PROT_READ if the
375          * page can be safely written.  However, it will force a read-only
376          * mapping for a read fault if the memory is managed by a virtual
377          * page table.
378          */
379         result = vm_fault_object(&fs, first_pindex, fault_type);
380
381         if (result == KERN_TRY_AGAIN)
382                 goto RetryFault;
383         if (result != KERN_SUCCESS)
384                 return (result);
385
386         /*
387          * On success vm_fault_object() does not unlock or deallocate, and fs.m
388          * will contain a busied page.
389          *
390          * Enter the page into the pmap and do pmap-related adjustments.
391          */
392         pmap_enter(fs.map->pmap, vaddr, fs.m, fs.prot, fs.wired);
393
394         /*
395          * Burst in a few more pages if possible.  The fs.map should still
396          * be locked.
397          */
398         if (fault_flags & VM_FAULT_BURST) {
399                 if ((fs.fault_flags & VM_FAULT_WIRE_MASK) == 0 &&
400                     fs.wired == 0) {
401                         vm_prefault(fs.map->pmap, vaddr, fs.entry, fs.prot);
402                 }
403         }
404         unlock_things(&fs);
405
406         vm_page_flag_clear(fs.m, PG_ZERO);
407         vm_page_flag_set(fs.m, PG_REFERENCED);
408
409         /*
410          * If the page is not wired down, then put it where the pageout daemon
411          * can find it.
412          */
413         if (fs.fault_flags & VM_FAULT_WIRE_MASK) {
414                 if (fs.wired)
415                         vm_page_wire(fs.m);
416                 else
417                         vm_page_unwire(fs.m, 1);
418         } else {
419                 vm_page_activate(fs.m);
420         }
421
422         if (curthread->td_lwp) {
423                 if (fs.hardfault) {
424                         curthread->td_lwp->lwp_ru.ru_majflt++;
425                 } else {
426                         curthread->td_lwp->lwp_ru.ru_minflt++;
427                 }
428         }
429
430         /*
431          * Unlock everything, and return
432          */
433         vm_page_wakeup(fs.m);
434         vm_object_deallocate(fs.first_object);
435
436         return (KERN_SUCCESS);
437 }
438
439 /*
440  * Fault in the specified virtual address in the current process map, 
441  * returning a held VM page or NULL.  See vm_fault_page() for more 
442  * information.
443  */
444 vm_page_t
445 vm_fault_page_quick(vm_offset_t va, vm_prot_t fault_type, int *errorp)
446 {
447         struct lwp *lp = curthread->td_lwp;
448         vm_page_t m;
449
450         m = vm_fault_page(&lp->lwp_vmspace->vm_map, va, 
451                           fault_type, VM_FAULT_NORMAL, errorp);
452         return(m);
453 }
454
455 /*
456  * Fault in the specified virtual address in the specified map, doing all
457  * necessary manipulation of the object store and all necessary I/O.  Return
458  * a held VM page or NULL, and set *errorp.  The related pmap is not
459  * updated.
460  *
461  * The returned page will be properly dirtied if VM_PROT_WRITE was specified,
462  * and marked PG_REFERENCED as well.
463  *
464  * If the page cannot be faulted writable and VM_PROT_WRITE was specified, an
465  * error will be returned.
466  */
467 vm_page_t
468 vm_fault_page(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
469               int fault_flags, int *errorp)
470 {
471         vm_pindex_t first_pindex;
472         struct faultstate fs;
473         int result;
474         vm_prot_t orig_fault_type = fault_type;
475
476         mycpu->gd_cnt.v_vm_faults++;
477
478         fs.didlimit = 0;
479         fs.hardfault = 0;
480         fs.fault_flags = fault_flags;
481         KKASSERT((fault_flags & VM_FAULT_WIRE_MASK) == 0);
482
483 RetryFault:
484         /*
485          * Find the vm_map_entry representing the backing store and resolve
486          * the top level object and page index.  This may have the side
487          * effect of executing a copy-on-write on the map entry and/or
488          * creating a shadow object, but will not COW any actual VM pages.
489          *
490          * On success fs.map is left read-locked and various other fields 
491          * are initialized but not otherwise referenced or locked.
492          *
493          * NOTE!  vm_map_lookup will upgrade the fault_type to VM_FAULT_WRITE
494          * if the map entry is a virtual page table and also writable,
495          * so we can set the 'A'accessed bit in the virtual page table entry.
496          */
497         fs.map = map;
498         result = vm_map_lookup(&fs.map, vaddr, fault_type,
499                                &fs.entry, &fs.first_object,
500                                &first_pindex, &fs.first_prot, &fs.wired);
501
502         if (result != KERN_SUCCESS) {
503                 *errorp = result;
504                 return (NULL);
505         }
506
507         /*
508          * fs.map is read-locked
509          *
510          * Misc checks.  Save the map generation number to detect races.
511          */
512         fs.map_generation = fs.map->timestamp;
513
514         if (fs.entry->eflags & MAP_ENTRY_NOFAULT) {
515                 panic("vm_fault: fault on nofault entry, addr: %lx",
516                     (u_long)vaddr);
517         }
518
519         /*
520          * A system map entry may return a NULL object.  No object means
521          * no pager means an unrecoverable kernel fault.
522          */
523         if (fs.first_object == NULL) {
524                 panic("vm_fault: unrecoverable fault at %p in entry %p",
525                         (void *)vaddr, fs.entry);
526         }
527
528         /*
529          * Make a reference to this object to prevent its disposal while we
530          * are messing with it.  Once we have the reference, the map is free
531          * to be diddled.  Since objects reference their shadows (and copies),
532          * they will stay around as well.
533          *
534          * Bump the paging-in-progress count to prevent size changes (e.g.
535          * truncation operations) during I/O.  This must be done after
536          * obtaining the vnode lock in order to avoid possible deadlocks.
537          */
538         vm_object_reference(fs.first_object);
539         fs.vp = vnode_pager_lock(fs.first_object);
540         vm_object_pip_add(fs.first_object, 1);
541
542         fs.lookup_still_valid = TRUE;
543         fs.first_m = NULL;
544         fs.object = fs.first_object;    /* so unlock_and_deallocate works */
545
546         /*
547          * If the entry is wired we cannot change the page protection.
548          */
549         if (fs.wired)
550                 fault_type = fs.first_prot;
551
552         /*
553          * The page we want is at (first_object, first_pindex), but if the
554          * vm_map_entry is VM_MAPTYPE_VPAGETABLE we have to traverse the
555          * page table to figure out the actual pindex.
556          *
557          * NOTE!  DEVELOPMENT IN PROGRESS, THIS IS AN INITIAL IMPLEMENTATION
558          * ONLY
559          */
560         if (fs.entry->maptype == VM_MAPTYPE_VPAGETABLE) {
561                 result = vm_fault_vpagetable(&fs, &first_pindex,
562                                              fs.entry->aux.master_pde,
563                                              fault_type);
564                 if (result == KERN_TRY_AGAIN)
565                         goto RetryFault;
566                 if (result != KERN_SUCCESS) {
567                         *errorp = result;
568                         return (NULL);
569                 }
570         }
571
572         /*
573          * Now we have the actual (object, pindex), fault in the page.  If
574          * vm_fault_object() fails it will unlock and deallocate the FS
575          * data.   If it succeeds everything remains locked and fs->object
576          * will have an additinal PIP count if it is not equal to
577          * fs->first_object
578          */
579         result = vm_fault_object(&fs, first_pindex, fault_type);
580
581         if (result == KERN_TRY_AGAIN)
582                 goto RetryFault;
583         if (result != KERN_SUCCESS) {
584                 *errorp = result;
585                 return(NULL);
586         }
587
588         if ((orig_fault_type & VM_PROT_WRITE) &&
589             (fs.prot & VM_PROT_WRITE) == 0) {
590                 *errorp = KERN_PROTECTION_FAILURE;
591                 unlock_and_deallocate(&fs);
592                 return(NULL);
593         }
594
595         /*
596          * On success vm_fault_object() does not unlock or deallocate, and fs.m
597          * will contain a busied page.
598          */
599         unlock_things(&fs);
600
601         /*
602          * Return a held page.  We are not doing any pmap manipulation so do
603          * not set PG_MAPPED.  However, adjust the page flags according to
604          * the fault type because the caller may not use a managed pmapping
605          * (so we don't want to lose the fact that the page will be dirtied
606          * if a write fault was specified).
607          */
608         vm_page_hold(fs.m);
609         vm_page_flag_clear(fs.m, PG_ZERO);
610         if (fault_type & VM_PROT_WRITE)
611                 vm_page_dirty(fs.m);
612
613         /*
614          * Update the pmap.  We really only have to do this if a COW
615          * occured to replace the read-only page with the new page.  For
616          * now just do it unconditionally. XXX
617          */
618         pmap_enter(fs.map->pmap, vaddr, fs.m, fs.prot, fs.wired);
619         vm_page_flag_set(fs.m, PG_REFERENCED);
620
621         /*
622          * Unbusy the page by activating it.  It remains held and will not
623          * be reclaimed.
624          */
625         vm_page_activate(fs.m);
626
627         if (curthread->td_lwp) {
628                 if (fs.hardfault) {
629                         curthread->td_lwp->lwp_ru.ru_majflt++;
630                 } else {
631                         curthread->td_lwp->lwp_ru.ru_minflt++;
632                 }
633         }
634
635         /*
636          * Unlock everything, and return the held page.
637          */
638         vm_page_wakeup(fs.m);
639         vm_object_deallocate(fs.first_object);
640
641         *errorp = 0;
642         return(fs.m);
643 }
644
645 /*
646  * Fault in the specified (object,offset), dirty the returned page as
647  * needed.  If the requested fault_type cannot be done NULL and an
648  * error is returned.
649  */
650 vm_page_t
651 vm_fault_object_page(vm_object_t object, vm_ooffset_t offset,
652                      vm_prot_t fault_type, int fault_flags, int *errorp)
653 {
654         int result;
655         vm_pindex_t first_pindex;
656         struct faultstate fs;
657         struct vm_map_entry entry;
658
659         bzero(&entry, sizeof(entry));
660         entry.object.vm_object = object;
661         entry.maptype = VM_MAPTYPE_NORMAL;
662         entry.protection = entry.max_protection = fault_type;
663
664         fs.didlimit = 0;
665         fs.hardfault = 0;
666         fs.fault_flags = fault_flags;
667         fs.map = NULL;
668         KKASSERT((fault_flags & VM_FAULT_WIRE_MASK) == 0);
669
670 RetryFault:
671         
672         fs.first_object = object;
673         first_pindex = OFF_TO_IDX(offset);
674         fs.entry = &entry;
675         fs.first_prot = fault_type;
676         fs.wired = 0;
677         /*fs.map_generation = 0; unused */
678
679         /*
680          * Make a reference to this object to prevent its disposal while we
681          * are messing with it.  Once we have the reference, the map is free
682          * to be diddled.  Since objects reference their shadows (and copies),
683          * they will stay around as well.
684          *
685          * Bump the paging-in-progress count to prevent size changes (e.g.
686          * truncation operations) during I/O.  This must be done after
687          * obtaining the vnode lock in order to avoid possible deadlocks.
688          */
689         vm_object_reference(fs.first_object);
690         fs.vp = vnode_pager_lock(fs.first_object);
691         vm_object_pip_add(fs.first_object, 1);
692
693         fs.lookup_still_valid = TRUE;
694         fs.first_m = NULL;
695         fs.object = fs.first_object;    /* so unlock_and_deallocate works */
696
697 #if 0
698         /* XXX future - ability to operate on VM object using vpagetable */
699         if (fs.entry->maptype == VM_MAPTYPE_VPAGETABLE) {
700                 result = vm_fault_vpagetable(&fs, &first_pindex,
701                                              fs.entry->aux.master_pde,
702                                              fault_type);
703                 if (result == KERN_TRY_AGAIN)
704                         goto RetryFault;
705                 if (result != KERN_SUCCESS) {
706                         *errorp = result;
707                         return (NULL);
708                 }
709         }
710 #endif
711
712         /*
713          * Now we have the actual (object, pindex), fault in the page.  If
714          * vm_fault_object() fails it will unlock and deallocate the FS
715          * data.   If it succeeds everything remains locked and fs->object
716          * will have an additinal PIP count if it is not equal to
717          * fs->first_object
718          */
719         result = vm_fault_object(&fs, first_pindex, fault_type);
720
721         if (result == KERN_TRY_AGAIN)
722                 goto RetryFault;
723         if (result != KERN_SUCCESS) {
724                 *errorp = result;
725                 return(NULL);
726         }
727
728         if ((fault_type & VM_PROT_WRITE) && (fs.prot & VM_PROT_WRITE) == 0) {
729                 *errorp = KERN_PROTECTION_FAILURE;
730                 unlock_and_deallocate(&fs);
731                 return(NULL);
732         }
733
734         /*
735          * On success vm_fault_object() does not unlock or deallocate, and fs.m
736          * will contain a busied page.
737          */
738         unlock_things(&fs);
739
740         /*
741          * Return a held page.  We are not doing any pmap manipulation so do
742          * not set PG_MAPPED.  However, adjust the page flags according to
743          * the fault type because the caller may not use a managed pmapping
744          * (so we don't want to lose the fact that the page will be dirtied
745          * if a write fault was specified).
746          */
747         vm_page_hold(fs.m);
748         vm_page_flag_clear(fs.m, PG_ZERO);
749         if (fault_type & VM_PROT_WRITE)
750                 vm_page_dirty(fs.m);
751
752         /*
753          * Indicate that the page was accessed.
754          */
755         vm_page_flag_set(fs.m, PG_REFERENCED);
756
757         /*
758          * Unbusy the page by activating it.  It remains held and will not
759          * be reclaimed.
760          */
761         vm_page_activate(fs.m);
762
763         if (curthread->td_lwp) {
764                 if (fs.hardfault) {
765                         mycpu->gd_cnt.v_vm_faults++;
766                         curthread->td_lwp->lwp_ru.ru_majflt++;
767                 } else {
768                         curthread->td_lwp->lwp_ru.ru_minflt++;
769                 }
770         }
771
772         /*
773          * Unlock everything, and return the held page.
774          */
775         vm_page_wakeup(fs.m);
776         vm_object_deallocate(fs.first_object);
777
778         *errorp = 0;
779         return(fs.m);
780 }
781
782 /*
783  * Translate the virtual page number (first_pindex) that is relative
784  * to the address space into a logical page number that is relative to the
785  * backing object.  Use the virtual page table pointed to by (vpte).
786  *
787  * This implements an N-level page table.  Any level can terminate the
788  * scan by setting VPTE_PS.   A linear mapping is accomplished by setting
789  * VPTE_PS in the master page directory entry set via mcontrol(MADV_SETMAP).
790  */
791 static
792 int
793 vm_fault_vpagetable(struct faultstate *fs, vm_pindex_t *pindex,
794                     vpte_t vpte, int fault_type)
795 {
796         struct lwbuf *lwb;
797         int vshift = 32 - PAGE_SHIFT;   /* page index bits remaining */
798         int result = KERN_SUCCESS;
799         vpte_t *ptep;
800
801         for (;;) {
802                 /*
803                  * We cannot proceed if the vpte is not valid, not readable
804                  * for a read fault, or not writable for a write fault.
805                  */
806                 if ((vpte & VPTE_V) == 0) {
807                         unlock_and_deallocate(fs);
808                         return (KERN_FAILURE);
809                 }
810                 if ((fault_type & VM_PROT_READ) && (vpte & VPTE_R) == 0) {
811                         unlock_and_deallocate(fs);
812                         return (KERN_FAILURE);
813                 }
814                 if ((fault_type & VM_PROT_WRITE) && (vpte & VPTE_W) == 0) {
815                         unlock_and_deallocate(fs);
816                         return (KERN_FAILURE);
817                 }
818                 if ((vpte & VPTE_PS) || vshift == 0)
819                         break;
820                 KKASSERT(vshift >= VPTE_PAGE_BITS);
821
822                 /*
823                  * Get the page table page.  Nominally we only read the page
824                  * table, but since we are actively setting VPTE_M and VPTE_A,
825                  * tell vm_fault_object() that we are writing it. 
826                  *
827                  * There is currently no real need to optimize this.
828                  */
829                 result = vm_fault_object(fs, vpte >> PAGE_SHIFT,
830                                          VM_PROT_READ|VM_PROT_WRITE);
831                 if (result != KERN_SUCCESS)
832                         return (result);
833
834                 /*
835                  * Process the returned fs.m and look up the page table
836                  * entry in the page table page.
837                  */
838                 vshift -= VPTE_PAGE_BITS;
839                 lwb = lwbuf_alloc(fs->m);
840                 ptep = ((vpte_t *)lwbuf_kva(lwb) +
841                         ((*pindex >> vshift) & VPTE_PAGE_MASK));
842                 vpte = *ptep;
843
844                 /*
845                  * Page table write-back.  If the vpte is valid for the
846                  * requested operation, do a write-back to the page table.
847                  *
848                  * XXX VPTE_M is not set properly for page directory pages.
849                  * It doesn't get set in the page directory if the page table
850                  * is modified during a read access.
851                  */
852                 if ((fault_type & VM_PROT_WRITE) && (vpte & VPTE_V) &&
853                     (vpte & VPTE_W)) {
854                         if ((vpte & (VPTE_M|VPTE_A)) != (VPTE_M|VPTE_A)) {
855                                 atomic_set_int(ptep, VPTE_M|VPTE_A);
856                                 vm_page_dirty(fs->m);
857                         }
858                 }
859                 if ((fault_type & VM_PROT_READ) && (vpte & VPTE_V) &&
860                     (vpte & VPTE_R)) {
861                         if ((vpte & VPTE_A) == 0) {
862                                 atomic_set_int(ptep, VPTE_A);
863                                 vm_page_dirty(fs->m);
864                         }
865                 }
866                 lwbuf_free(lwb);
867                 vm_page_flag_set(fs->m, PG_REFERENCED);
868                 vm_page_activate(fs->m);
869                 vm_page_wakeup(fs->m);
870                 cleanup_successful_fault(fs);
871         }
872         /*
873          * Combine remaining address bits with the vpte.
874          */
875         *pindex = (vpte >> PAGE_SHIFT) +
876                   (*pindex & ((1 << vshift) - 1));
877         return (KERN_SUCCESS);
878 }
879
880
881 /*
882  * Do all operations required to fault-in (fs.first_object, pindex).  Run
883  * through the shadow chain as necessary and do required COW or virtual
884  * copy operations.  The caller has already fully resolved the vm_map_entry
885  * and, if appropriate, has created a copy-on-write layer.  All we need to
886  * do is iterate the object chain.
887  *
888  * On failure (fs) is unlocked and deallocated and the caller may return or
889  * retry depending on the failure code.  On success (fs) is NOT unlocked or
890  * deallocated, fs.m will contained a resolved, busied page, and fs.object
891  * will have an additional PIP count if it is not equal to fs.first_object.
892  */
893 static
894 int
895 vm_fault_object(struct faultstate *fs,
896                 vm_pindex_t first_pindex, vm_prot_t fault_type)
897 {
898         vm_object_t next_object;
899         vm_pindex_t pindex;
900
901         fs->prot = fs->first_prot;
902         fs->object = fs->first_object;
903         pindex = first_pindex;
904
905         /* 
906          * If a read fault occurs we try to make the page writable if
907          * possible.  There are three cases where we cannot make the
908          * page mapping writable:
909          *
910          * (1) The mapping is read-only or the VM object is read-only,
911          *     fs->prot above will simply not have VM_PROT_WRITE set.
912          *
913          * (2) If the mapping is a virtual page table we need to be able
914          *     to detect writes so we can set VPTE_M in the virtual page
915          *     table.
916          *
917          * (3) If the VM page is read-only or copy-on-write, upgrading would
918          *     just result in an unnecessary COW fault.
919          *
920          * VM_PROT_VPAGED is set if faulting via a virtual page table and
921          * causes adjustments to the 'M'odify bit to also turn off write
922          * access to force a re-fault.
923          */
924         if (fs->entry->maptype == VM_MAPTYPE_VPAGETABLE) {
925                 if ((fault_type & VM_PROT_WRITE) == 0)
926                         fs->prot &= ~VM_PROT_WRITE;
927         }
928
929         for (;;) {
930                 /*
931                  * If the object is dead, we stop here
932                  */
933                 if (fs->object->flags & OBJ_DEAD) {
934                         unlock_and_deallocate(fs);
935                         return (KERN_PROTECTION_FAILURE);
936                 }
937
938                 /*
939                  * See if page is resident.  spl protection is required
940                  * to avoid an interrupt unbusy/free race against our
941                  * lookup.  We must hold the protection through a page
942                  * allocation or busy.
943                  */
944                 crit_enter();
945                 fs->m = vm_page_lookup(fs->object, pindex);
946                 if (fs->m != NULL) {
947                         int queue;
948                         /*
949                          * Wait/Retry if the page is busy.  We have to do this
950                          * if the page is busy via either PG_BUSY or 
951                          * vm_page_t->busy because the vm_pager may be using
952                          * vm_page_t->busy for pageouts ( and even pageins if
953                          * it is the vnode pager ), and we could end up trying
954                          * to pagein and pageout the same page simultaneously.
955                          *
956                          * We can theoretically allow the busy case on a read
957                          * fault if the page is marked valid, but since such
958                          * pages are typically already pmap'd, putting that
959                          * special case in might be more effort then it is 
960                          * worth.  We cannot under any circumstances mess
961                          * around with a vm_page_t->busy page except, perhaps,
962                          * to pmap it.
963                          */
964                         if ((fs->m->flags & PG_BUSY) || fs->m->busy) {
965                                 unlock_things(fs);
966                                 vm_page_sleep_busy(fs->m, TRUE, "vmpfw");
967                                 mycpu->gd_cnt.v_intrans++;
968                                 vm_object_deallocate(fs->first_object);
969                                 fs->first_object = NULL;
970                                 crit_exit();
971                                 return (KERN_TRY_AGAIN);
972                         }
973
974                         /*
975                          * If reactivating a page from PQ_CACHE we may have
976                          * to rate-limit.
977                          */
978                         queue = fs->m->queue;
979                         vm_page_unqueue_nowakeup(fs->m);
980
981                         if ((queue - fs->m->pc) == PQ_CACHE && 
982                             vm_page_count_severe()) {
983                                 vm_page_activate(fs->m);
984                                 unlock_and_deallocate(fs);
985                                 vm_waitpfault();
986                                 crit_exit();
987                                 return (KERN_TRY_AGAIN);
988                         }
989
990                         /*
991                          * Mark page busy for other processes, and the 
992                          * pagedaemon.  If it still isn't completely valid
993                          * (readable), or if a read-ahead-mark is set on
994                          * the VM page, jump to readrest, else we found the
995                          * page and can return.
996                          *
997                          * We can release the spl once we have marked the
998                          * page busy.
999                          */
1000                         vm_page_busy(fs->m);
1001                         crit_exit();
1002
1003                         if (fs->m->object != &kernel_object) {
1004                                 if ((fs->m->valid & VM_PAGE_BITS_ALL) !=
1005                                     VM_PAGE_BITS_ALL) {
1006                                         goto readrest;
1007                                 }
1008                                 if (fs->m->flags & PG_RAM) {
1009                                         if (debug_cluster)
1010                                                 kprintf("R");
1011                                         vm_page_flag_clear(fs->m, PG_RAM);
1012                                         goto readrest;
1013                                 }
1014                         }
1015                         break; /* break to PAGE HAS BEEN FOUND */
1016                 }
1017
1018                 /*
1019                  * Page is not resident, If this is the search termination
1020                  * or the pager might contain the page, allocate a new page.
1021                  *
1022                  * NOTE: We are still in a critical section.
1023                  */
1024                 if (TRYPAGER(fs) || fs->object == fs->first_object) {
1025                         /*
1026                          * If the page is beyond the object size we fail
1027                          */
1028                         if (pindex >= fs->object->size) {
1029                                 crit_exit();
1030                                 unlock_and_deallocate(fs);
1031                                 return (KERN_PROTECTION_FAILURE);
1032                         }
1033
1034                         /*
1035                          * Ratelimit.
1036                          */
1037                         if (fs->didlimit == 0 && curproc != NULL) {
1038                                 int limticks;
1039
1040                                 limticks = vm_fault_ratelimit(curproc->p_vmspace);
1041                                 if (limticks) {
1042                                         crit_exit();
1043                                         unlock_and_deallocate(fs);
1044                                         tsleep(curproc, 0, "vmrate", limticks);
1045                                         fs->didlimit = 1;
1046                                         return (KERN_TRY_AGAIN);
1047                                 }
1048                         }
1049
1050                         /*
1051                          * Allocate a new page for this object/offset pair.
1052                          */
1053                         fs->m = NULL;
1054                         if (!vm_page_count_severe()) {
1055                                 fs->m = vm_page_alloc(fs->object, pindex,
1056                                     (fs->vp || fs->object->backing_object) ? VM_ALLOC_NORMAL : VM_ALLOC_NORMAL | VM_ALLOC_ZERO);
1057                         }
1058                         if (fs->m == NULL) {
1059                                 crit_exit();
1060                                 unlock_and_deallocate(fs);
1061                                 vm_waitpfault();
1062                                 return (KERN_TRY_AGAIN);
1063                         }
1064                 }
1065                 crit_exit();
1066
1067 readrest:
1068                 /*
1069                  * We have found an invalid or partially valid page, a
1070                  * page with a read-ahead mark which might be partially or
1071                  * fully valid (and maybe dirty too), or we have allocated
1072                  * a new page.
1073                  *
1074                  * Attempt to fault-in the page if there is a chance that the
1075                  * pager has it, and potentially fault in additional pages
1076                  * at the same time.
1077                  *
1078                  * We are NOT in splvm here and if TRYPAGER is true then
1079                  * fs.m will be non-NULL and will be PG_BUSY for us.
1080                  */
1081                 if (TRYPAGER(fs)) {
1082                         int rv;
1083                         int seqaccess;
1084                         u_char behavior = vm_map_entry_behavior(fs->entry);
1085
1086                         if (behavior == MAP_ENTRY_BEHAV_RANDOM)
1087                                 seqaccess = 0;
1088                         else
1089                                 seqaccess = -1;
1090
1091                         /*
1092                          * If sequential access is detected then attempt
1093                          * to deactivate/cache pages behind the scan to
1094                          * prevent resource hogging.
1095                          *
1096                          * Use of PG_RAM to detect sequential access
1097                          * also simulates multi-zone sequential access
1098                          * detection for free.
1099                          *
1100                          * NOTE: Partially valid dirty pages cannot be
1101                          *       deactivated without causing NFS picemeal
1102                          *       writes to barf.
1103                          */
1104                         if ((fs->first_object->type != OBJT_DEVICE) &&
1105                             (behavior == MAP_ENTRY_BEHAV_SEQUENTIAL ||
1106                                 (behavior != MAP_ENTRY_BEHAV_RANDOM &&
1107                                  (fs->m->flags & PG_RAM)))
1108                         ) {
1109                                 vm_pindex_t scan_pindex;
1110                                 int scan_count = 16;
1111
1112                                 if (first_pindex < 16) {
1113                                         scan_pindex = 0;
1114                                         scan_count = 0;
1115                                 } else {
1116                                         scan_pindex = first_pindex - 16;
1117                                         if (scan_pindex < 16)
1118                                                 scan_count = scan_pindex;
1119                                         else
1120                                                 scan_count = 16;
1121                                 }
1122
1123                                 crit_enter();
1124                                 while (scan_count) {
1125                                         vm_page_t mt;
1126
1127                                         mt = vm_page_lookup(fs->first_object,
1128                                                             scan_pindex);
1129                                         if (mt == NULL ||
1130                                             (mt->valid != VM_PAGE_BITS_ALL)) {
1131                                                 break;
1132                                         }
1133                                         if (mt->busy ||
1134                                             (mt->flags & (PG_BUSY | PG_FICTITIOUS | PG_UNMANAGED)) ||
1135                                             mt->hold_count ||
1136                                             mt->wire_count)  {
1137                                                 goto skip;
1138                                         }
1139                                         if (mt->dirty == 0)
1140                                                 vm_page_test_dirty(mt);
1141                                         if (mt->dirty) {
1142                                                 vm_page_busy(mt);
1143                                                 vm_page_protect(mt,
1144                                                                 VM_PROT_NONE);
1145                                                 vm_page_deactivate(mt);
1146                                                 vm_page_wakeup(mt);
1147                                         } else {
1148                                                 vm_page_cache(mt);
1149                                         }
1150 skip:
1151                                         --scan_count;
1152                                         --scan_pindex;
1153                                 }
1154                                 crit_exit();
1155
1156                                 seqaccess = 1;
1157                         }
1158
1159                         /*
1160                          * Avoid deadlocking against the map when doing I/O.
1161                          * fs.object and the page is PG_BUSY'd.
1162                          */
1163                         unlock_map(fs);
1164
1165                         /*
1166                          * Acquire the page data.  We still hold a ref on
1167                          * fs.object and the page has been PG_BUSY's.
1168                          *
1169                          * The pager may replace the page (for example, in
1170                          * order to enter a fictitious page into the
1171                          * object).  If it does so it is responsible for
1172                          * cleaning up the passed page and properly setting
1173                          * the new page PG_BUSY.
1174                          *
1175                          * If we got here through a PG_RAM read-ahead
1176                          * mark the page may be partially dirty and thus
1177                          * not freeable.  Don't bother checking to see
1178                          * if the pager has the page because we can't free
1179                          * it anyway.  We have to depend on the get_page
1180                          * operation filling in any gaps whether there is
1181                          * backing store or not.
1182                          */
1183                         rv = vm_pager_get_page(fs->object, &fs->m, seqaccess);
1184
1185                         if (rv == VM_PAGER_OK) {
1186                                 /*
1187                                  * Relookup in case pager changed page. Pager
1188                                  * is responsible for disposition of old page
1189                                  * if moved.
1190                                  *
1191                                  * XXX other code segments do relookups too.
1192                                  * It's a bad abstraction that needs to be
1193                                  * fixed/removed.
1194                                  */
1195                                 fs->m = vm_page_lookup(fs->object, pindex);
1196                                 if (fs->m == NULL) {
1197                                         unlock_and_deallocate(fs);
1198                                         return (KERN_TRY_AGAIN);
1199                                 }
1200
1201                                 ++fs->hardfault;
1202                                 break; /* break to PAGE HAS BEEN FOUND */
1203                         }
1204
1205                         /*
1206                          * Remove the bogus page (which does not exist at this
1207                          * object/offset); before doing so, we must get back
1208                          * our object lock to preserve our invariant.
1209                          *
1210                          * Also wake up any other process that may want to bring
1211                          * in this page.
1212                          *
1213                          * If this is the top-level object, we must leave the
1214                          * busy page to prevent another process from rushing
1215                          * past us, and inserting the page in that object at
1216                          * the same time that we are.
1217                          */
1218                         if (rv == VM_PAGER_ERROR) {
1219                                 if (curproc)
1220                                         kprintf("vm_fault: pager read error, pid %d (%s)\n", curproc->p_pid, curproc->p_comm);
1221                                 else
1222                                         kprintf("vm_fault: pager read error, thread %p (%s)\n", curthread, curproc->p_comm);
1223                         }
1224
1225                         /*
1226                          * Data outside the range of the pager or an I/O error
1227                          *
1228                          * The page may have been wired during the pagein,
1229                          * e.g. by the buffer cache, and cannot simply be
1230                          * freed.  Call vnode_pager_freepage() to deal with it.
1231                          */
1232                         /*
1233                          * XXX - the check for kernel_map is a kludge to work
1234                          * around having the machine panic on a kernel space
1235                          * fault w/ I/O error.
1236                          */
1237                         if (((fs->map != &kernel_map) &&
1238                             (rv == VM_PAGER_ERROR)) || (rv == VM_PAGER_BAD)) {
1239                                 vnode_pager_freepage(fs->m);
1240                                 fs->m = NULL;
1241                                 unlock_and_deallocate(fs);
1242                                 if (rv == VM_PAGER_ERROR)
1243                                         return (KERN_FAILURE);
1244                                 else
1245                                         return (KERN_PROTECTION_FAILURE);
1246                                 /* NOT REACHED */
1247                         }
1248                         if (fs->object != fs->first_object) {
1249                                 vnode_pager_freepage(fs->m);
1250                                 fs->m = NULL;
1251                                 /*
1252                                  * XXX - we cannot just fall out at this
1253                                  * point, m has been freed and is invalid!
1254                                  */
1255                         }
1256                 }
1257
1258                 /*
1259                  * We get here if the object has a default pager (or unwiring) 
1260                  * or the pager doesn't have the page.
1261                  */
1262                 if (fs->object == fs->first_object)
1263                         fs->first_m = fs->m;
1264
1265                 /*
1266                  * Move on to the next object.  Lock the next object before
1267                  * unlocking the current one.
1268                  */
1269                 pindex += OFF_TO_IDX(fs->object->backing_object_offset);
1270                 next_object = fs->object->backing_object;
1271                 if (next_object == NULL) {
1272                         /*
1273                          * If there's no object left, fill the page in the top
1274                          * object with zeros.
1275                          */
1276                         if (fs->object != fs->first_object) {
1277                                 vm_object_pip_wakeup(fs->object);
1278
1279                                 fs->object = fs->first_object;
1280                                 pindex = first_pindex;
1281                                 fs->m = fs->first_m;
1282                         }
1283                         fs->first_m = NULL;
1284
1285                         /*
1286                          * Zero the page if necessary and mark it valid.
1287                          */
1288                         if ((fs->m->flags & PG_ZERO) == 0) {
1289                                 vm_page_zero_fill(fs->m);
1290                         } else {
1291                                 mycpu->gd_cnt.v_ozfod++;
1292                         }
1293                         mycpu->gd_cnt.v_zfod++;
1294                         fs->m->valid = VM_PAGE_BITS_ALL;
1295                         break;  /* break to PAGE HAS BEEN FOUND */
1296                 } else {
1297                         if (fs->object != fs->first_object) {
1298                                 vm_object_pip_wakeup(fs->object);
1299                         }
1300                         KASSERT(fs->object != next_object, ("object loop %p", next_object));
1301                         fs->object = next_object;
1302                         vm_object_pip_add(fs->object, 1);
1303                 }
1304         }
1305
1306         /*
1307          * PAGE HAS BEEN FOUND. [Loop invariant still holds -- the object lock
1308          * is held.]
1309          *
1310          * If the page is being written, but isn't already owned by the
1311          * top-level object, we have to copy it into a new page owned by the
1312          * top-level object.
1313          */
1314         KASSERT((fs->m->flags & PG_BUSY) != 0,
1315                 ("vm_fault: not busy after main loop"));
1316
1317         if (fs->object != fs->first_object) {
1318                 /*
1319                  * We only really need to copy if we want to write it.
1320                  */
1321                 if (fault_type & VM_PROT_WRITE) {
1322                         /*
1323                          * This allows pages to be virtually copied from a 
1324                          * backing_object into the first_object, where the 
1325                          * backing object has no other refs to it, and cannot
1326                          * gain any more refs.  Instead of a bcopy, we just 
1327                          * move the page from the backing object to the 
1328                          * first object.  Note that we must mark the page 
1329                          * dirty in the first object so that it will go out 
1330                          * to swap when needed.
1331                          */
1332                         if (
1333                                 /*
1334                                  * Map, if present, has not changed
1335                                  */
1336                                 (fs->map == NULL ||
1337                                 fs->map_generation == fs->map->timestamp) &&
1338                                 /*
1339                                  * Only one shadow object
1340                                  */
1341                                 (fs->object->shadow_count == 1) &&
1342                                 /*
1343                                  * No COW refs, except us
1344                                  */
1345                                 (fs->object->ref_count == 1) &&
1346                                 /*
1347                                  * No one else can look this object up
1348                                  */
1349                                 (fs->object->handle == NULL) &&
1350                                 /*
1351                                  * No other ways to look the object up
1352                                  */
1353                                 ((fs->object->type == OBJT_DEFAULT) ||
1354                                  (fs->object->type == OBJT_SWAP)) &&
1355                                 /*
1356                                  * We don't chase down the shadow chain
1357                                  */
1358                                 (fs->object == fs->first_object->backing_object) &&
1359
1360                                 /*
1361                                  * grab the lock if we need to
1362                                  */
1363                                 (fs->lookup_still_valid ||
1364                                  fs->map == NULL ||
1365                                  lockmgr(&fs->map->lock, LK_EXCLUSIVE|LK_NOWAIT) == 0)
1366                             ) {
1367                                 
1368                                 fs->lookup_still_valid = 1;
1369                                 /*
1370                                  * get rid of the unnecessary page
1371                                  */
1372                                 vm_page_protect(fs->first_m, VM_PROT_NONE);
1373                                 vm_page_free(fs->first_m);
1374                                 fs->first_m = NULL;
1375
1376                                 /*
1377                                  * grab the page and put it into the 
1378                                  * process'es object.  The page is 
1379                                  * automatically made dirty.
1380                                  */
1381                                 vm_page_rename(fs->m, fs->first_object, first_pindex);
1382                                 fs->first_m = fs->m;
1383                                 vm_page_busy(fs->first_m);
1384                                 fs->m = NULL;
1385                                 mycpu->gd_cnt.v_cow_optim++;
1386                         } else {
1387                                 /*
1388                                  * Oh, well, lets copy it.
1389                                  */
1390                                 vm_page_copy(fs->m, fs->first_m);
1391                                 vm_page_event(fs->m, VMEVENT_COW);
1392                         }
1393
1394                         if (fs->m) {
1395                                 /*
1396                                  * We no longer need the old page or object.
1397                                  */
1398                                 release_page(fs);
1399                         }
1400
1401                         /*
1402                          * fs->object != fs->first_object due to above 
1403                          * conditional
1404                          */
1405                         vm_object_pip_wakeup(fs->object);
1406
1407                         /*
1408                          * Only use the new page below...
1409                          */
1410
1411                         mycpu->gd_cnt.v_cow_faults++;
1412                         fs->m = fs->first_m;
1413                         fs->object = fs->first_object;
1414                         pindex = first_pindex;
1415                 } else {
1416                         /*
1417                          * If it wasn't a write fault avoid having to copy
1418                          * the page by mapping it read-only.
1419                          */
1420                         fs->prot &= ~VM_PROT_WRITE;
1421                 }
1422         }
1423
1424         /*
1425          * We may have had to unlock a map to do I/O.  If we did then
1426          * lookup_still_valid will be FALSE.  If the map generation count
1427          * also changed then all sorts of things could have happened while
1428          * we were doing the I/O and we need to retry.
1429          */
1430
1431         if (!fs->lookup_still_valid &&
1432             fs->map != NULL &&
1433             (fs->map->timestamp != fs->map_generation)) {
1434                 release_page(fs);
1435                 unlock_and_deallocate(fs);
1436                 return (KERN_TRY_AGAIN);
1437         }
1438
1439         /*
1440          * If the fault is a write, we know that this page is being
1441          * written NOW so dirty it explicitly to save on pmap_is_modified()
1442          * calls later.
1443          *
1444          * If this is a NOSYNC mmap we do not want to set PG_NOSYNC
1445          * if the page is already dirty to prevent data written with
1446          * the expectation of being synced from not being synced.
1447          * Likewise if this entry does not request NOSYNC then make
1448          * sure the page isn't marked NOSYNC.  Applications sharing
1449          * data should use the same flags to avoid ping ponging.
1450          *
1451          * Also tell the backing pager, if any, that it should remove
1452          * any swap backing since the page is now dirty.
1453          */
1454         if (fs->prot & VM_PROT_WRITE) {
1455                 vm_object_set_writeable_dirty(fs->m->object);
1456                 if (fs->entry->eflags & MAP_ENTRY_NOSYNC) {
1457                         if (fs->m->dirty == 0)
1458                                 vm_page_flag_set(fs->m, PG_NOSYNC);
1459                 } else {
1460                         vm_page_flag_clear(fs->m, PG_NOSYNC);
1461                 }
1462                 if (fs->fault_flags & VM_FAULT_DIRTY) {
1463                         crit_enter();
1464                         vm_page_dirty(fs->m);
1465                         swap_pager_unswapped(fs->m);
1466                         crit_exit();
1467                 }
1468         }
1469
1470         /*
1471          * Page had better still be busy.  We are still locked up and 
1472          * fs->object will have another PIP reference if it is not equal
1473          * to fs->first_object.
1474          */
1475         KASSERT(fs->m->flags & PG_BUSY,
1476                 ("vm_fault: page %p not busy!", fs->m));
1477
1478         /*
1479          * Sanity check: page must be completely valid or it is not fit to
1480          * map into user space.  vm_pager_get_pages() ensures this.
1481          */
1482         if (fs->m->valid != VM_PAGE_BITS_ALL) {
1483                 vm_page_zero_invalid(fs->m, TRUE);
1484                 kprintf("Warning: page %p partially invalid on fault\n", fs->m);
1485         }
1486
1487         return (KERN_SUCCESS);
1488 }
1489
1490 /*
1491  * Wire down a range of virtual addresses in a map.  The entry in question
1492  * should be marked in-transition and the map must be locked.  We must
1493  * release the map temporarily while faulting-in the page to avoid a
1494  * deadlock.  Note that the entry may be clipped while we are blocked but
1495  * will never be freed.
1496  */
1497 int
1498 vm_fault_wire(vm_map_t map, vm_map_entry_t entry, boolean_t user_wire)
1499 {
1500         boolean_t fictitious;
1501         vm_offset_t start;
1502         vm_offset_t end;
1503         vm_offset_t va;
1504         vm_paddr_t pa;
1505         pmap_t pmap;
1506         int rv;
1507
1508         pmap = vm_map_pmap(map);
1509         start = entry->start;
1510         end = entry->end;
1511         fictitious = entry->object.vm_object &&
1512                         (entry->object.vm_object->type == OBJT_DEVICE);
1513
1514         vm_map_unlock(map);
1515         map->timestamp++;
1516
1517         /*
1518          * We simulate a fault to get the page and enter it in the physical
1519          * map.
1520          */
1521         for (va = start; va < end; va += PAGE_SIZE) {
1522                 if (user_wire) {
1523                         rv = vm_fault(map, va, VM_PROT_READ, 
1524                                         VM_FAULT_USER_WIRE);
1525                 } else {
1526                         rv = vm_fault(map, va, VM_PROT_READ|VM_PROT_WRITE,
1527                                         VM_FAULT_CHANGE_WIRING);
1528                 }
1529                 if (rv) {
1530                         while (va > start) {
1531                                 va -= PAGE_SIZE;
1532                                 if ((pa = pmap_extract(pmap, va)) == 0)
1533                                         continue;
1534                                 pmap_change_wiring(pmap, va, FALSE);
1535                                 if (!fictitious)
1536                                         vm_page_unwire(PHYS_TO_VM_PAGE(pa), 1);
1537                         }
1538                         vm_map_lock(map);
1539                         return (rv);
1540                 }
1541         }
1542         vm_map_lock(map);
1543         return (KERN_SUCCESS);
1544 }
1545
1546 /*
1547  * Unwire a range of virtual addresses in a map.  The map should be
1548  * locked.
1549  */
1550 void
1551 vm_fault_unwire(vm_map_t map, vm_map_entry_t entry)
1552 {
1553         boolean_t fictitious;
1554         vm_offset_t start;
1555         vm_offset_t end;
1556         vm_offset_t va;
1557         vm_paddr_t pa;
1558         pmap_t pmap;
1559
1560         pmap = vm_map_pmap(map);
1561         start = entry->start;
1562         end = entry->end;
1563         fictitious = entry->object.vm_object &&
1564                         (entry->object.vm_object->type == OBJT_DEVICE);
1565
1566         /*
1567          * Since the pages are wired down, we must be able to get their
1568          * mappings from the physical map system.
1569          */
1570         for (va = start; va < end; va += PAGE_SIZE) {
1571                 pa = pmap_extract(pmap, va);
1572                 if (pa != 0) {
1573                         pmap_change_wiring(pmap, va, FALSE);
1574                         if (!fictitious)
1575                                 vm_page_unwire(PHYS_TO_VM_PAGE(pa), 1);
1576                 }
1577         }
1578 }
1579
1580 /*
1581  * Reduce the rate at which memory is allocated to a process based
1582  * on the perceived load on the VM system. As the load increases
1583  * the allocation burst rate goes down and the delay increases. 
1584  *
1585  * Rate limiting does not apply when faulting active or inactive
1586  * pages.  When faulting 'cache' pages, rate limiting only applies
1587  * if the system currently has a severe page deficit.
1588  *
1589  * XXX vm_pagesupply should be increased when a page is freed.
1590  *
1591  * We sleep up to 1/10 of a second.
1592  */
1593 static int
1594 vm_fault_ratelimit(struct vmspace *vmspace)
1595 {
1596         if (vm_load_enable == 0)
1597                 return(0);
1598         if (vmspace->vm_pagesupply > 0) {
1599                 --vmspace->vm_pagesupply;
1600                 return(0);
1601         }
1602 #ifdef INVARIANTS
1603         if (vm_load_debug) {
1604                 kprintf("load %-4d give %d pgs, wait %d, pid %-5d (%s)\n",
1605                         vm_load, 
1606                         (1000 - vm_load ) / 10, vm_load * hz / 10000,
1607                         curproc->p_pid, curproc->p_comm);
1608         }
1609 #endif
1610         vmspace->vm_pagesupply = (1000 - vm_load) / 10;
1611         return(vm_load * hz / 10000);
1612 }
1613
1614 /*
1615  *      Routine:
1616  *              vm_fault_copy_entry
1617  *      Function:
1618  *              Copy all of the pages from a wired-down map entry to another.
1619  *
1620  *      In/out conditions:
1621  *              The source and destination maps must be locked for write.
1622  *              The source map entry must be wired down (or be a sharing map
1623  *              entry corresponding to a main map entry that is wired down).
1624  */
1625
1626 void
1627 vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map,
1628     vm_map_entry_t dst_entry, vm_map_entry_t src_entry)
1629 {
1630         vm_object_t dst_object;
1631         vm_object_t src_object;
1632         vm_ooffset_t dst_offset;
1633         vm_ooffset_t src_offset;
1634         vm_prot_t prot;
1635         vm_offset_t vaddr;
1636         vm_page_t dst_m;
1637         vm_page_t src_m;
1638
1639 #ifdef  lint
1640         src_map++;
1641 #endif  /* lint */
1642
1643         src_object = src_entry->object.vm_object;
1644         src_offset = src_entry->offset;
1645
1646         /*
1647          * Create the top-level object for the destination entry. (Doesn't
1648          * actually shadow anything - we copy the pages directly.)
1649          */
1650         vm_map_entry_allocate_object(dst_entry);
1651         dst_object = dst_entry->object.vm_object;
1652
1653         prot = dst_entry->max_protection;
1654
1655         /*
1656          * Loop through all of the pages in the entry's range, copying each
1657          * one from the source object (it should be there) to the destination
1658          * object.
1659          */
1660         for (vaddr = dst_entry->start, dst_offset = 0;
1661             vaddr < dst_entry->end;
1662             vaddr += PAGE_SIZE, dst_offset += PAGE_SIZE) {
1663
1664                 /*
1665                  * Allocate a page in the destination object
1666                  */
1667                 do {
1668                         dst_m = vm_page_alloc(dst_object,
1669                                 OFF_TO_IDX(dst_offset), VM_ALLOC_NORMAL);
1670                         if (dst_m == NULL) {
1671                                 vm_wait(0);
1672                         }
1673                 } while (dst_m == NULL);
1674
1675                 /*
1676                  * Find the page in the source object, and copy it in.
1677                  * (Because the source is wired down, the page will be in
1678                  * memory.)
1679                  */
1680                 src_m = vm_page_lookup(src_object,
1681                         OFF_TO_IDX(dst_offset + src_offset));
1682                 if (src_m == NULL)
1683                         panic("vm_fault_copy_wired: page missing");
1684
1685                 vm_page_copy(src_m, dst_m);
1686                 vm_page_event(src_m, VMEVENT_COW);
1687
1688                 /*
1689                  * Enter it in the pmap...
1690                  */
1691
1692                 vm_page_flag_clear(dst_m, PG_ZERO);
1693                 pmap_enter(dst_map->pmap, vaddr, dst_m, prot, FALSE);
1694
1695                 /*
1696                  * Mark it no longer busy, and put it on the active list.
1697                  */
1698                 vm_page_activate(dst_m);
1699                 vm_page_wakeup(dst_m);
1700         }
1701 }
1702
1703 #if 0
1704
1705 /*
1706  * This routine checks around the requested page for other pages that
1707  * might be able to be faulted in.  This routine brackets the viable
1708  * pages for the pages to be paged in.
1709  *
1710  * Inputs:
1711  *      m, rbehind, rahead
1712  *
1713  * Outputs:
1714  *  marray (array of vm_page_t), reqpage (index of requested page)
1715  *
1716  * Return value:
1717  *  number of pages in marray
1718  */
1719 static int
1720 vm_fault_additional_pages(vm_page_t m, int rbehind, int rahead,
1721                           vm_page_t *marray, int *reqpage)
1722 {
1723         int i,j;
1724         vm_object_t object;
1725         vm_pindex_t pindex, startpindex, endpindex, tpindex;
1726         vm_page_t rtm;
1727         int cbehind, cahead;
1728
1729         object = m->object;
1730         pindex = m->pindex;
1731
1732         /*
1733          * we don't fault-ahead for device pager
1734          */
1735         if (object->type == OBJT_DEVICE) {
1736                 *reqpage = 0;
1737                 marray[0] = m;
1738                 return 1;
1739         }
1740
1741         /*
1742          * if the requested page is not available, then give up now
1743          */
1744         if (!vm_pager_has_page(object, pindex, &cbehind, &cahead)) {
1745                 *reqpage = 0;   /* not used by caller, fix compiler warn */
1746                 return 0;
1747         }
1748
1749         if ((cbehind == 0) && (cahead == 0)) {
1750                 *reqpage = 0;
1751                 marray[0] = m;
1752                 return 1;
1753         }
1754
1755         if (rahead > cahead) {
1756                 rahead = cahead;
1757         }
1758
1759         if (rbehind > cbehind) {
1760                 rbehind = cbehind;
1761         }
1762
1763         /*
1764          * Do not do any readahead if we have insufficient free memory.
1765          *
1766          * XXX code was broken disabled before and has instability
1767          * with this conditonal fixed, so shortcut for now.
1768          */
1769         if (burst_fault == 0 || vm_page_count_severe()) {
1770                 marray[0] = m;
1771                 *reqpage = 0;
1772                 return 1;
1773         }
1774
1775         /*
1776          * scan backward for the read behind pages -- in memory 
1777          *
1778          * Assume that if the page is not found an interrupt will not
1779          * create it.  Theoretically interrupts can only remove (busy)
1780          * pages, not create new associations.
1781          */
1782         if (pindex > 0) {
1783                 if (rbehind > pindex) {
1784                         rbehind = pindex;
1785                         startpindex = 0;
1786                 } else {
1787                         startpindex = pindex - rbehind;
1788                 }
1789
1790                 crit_enter();
1791                 for (tpindex = pindex; tpindex > startpindex; --tpindex) {
1792                         if (vm_page_lookup(object, tpindex - 1))
1793                                 break;
1794                 }
1795
1796                 i = 0;
1797                 while (tpindex < pindex) {
1798                         rtm = vm_page_alloc(object, tpindex, VM_ALLOC_SYSTEM);
1799                         if (rtm == NULL) {
1800                                 crit_exit();
1801                                 for (j = 0; j < i; j++) {
1802                                         vm_page_free(marray[j]);
1803                                 }
1804                                 marray[0] = m;
1805                                 *reqpage = 0;
1806                                 return 1;
1807                         }
1808                         marray[i] = rtm;
1809                         ++i;
1810                         ++tpindex;
1811                 }
1812                 crit_exit();
1813         } else {
1814                 i = 0;
1815         }
1816
1817         /*
1818          * Assign requested page
1819          */
1820         marray[i] = m;
1821         *reqpage = i;
1822         ++i;
1823
1824         /*
1825          * Scan forwards for read-ahead pages
1826          */
1827         tpindex = pindex + 1;
1828         endpindex = tpindex + rahead;
1829         if (endpindex > object->size)
1830                 endpindex = object->size;
1831
1832         crit_enter();
1833         while (tpindex < endpindex) {
1834                 if (vm_page_lookup(object, tpindex))
1835                         break;
1836                 rtm = vm_page_alloc(object, tpindex, VM_ALLOC_SYSTEM);
1837                 if (rtm == NULL)
1838                         break;
1839                 marray[i] = rtm;
1840                 ++i;
1841                 ++tpindex;
1842         }
1843         crit_exit();
1844
1845         return (i);
1846 }
1847
1848 #endif
1849
1850 /*
1851  * vm_prefault() provides a quick way of clustering pagefaults into a
1852  * processes address space.  It is a "cousin" of pmap_object_init_pt,
1853  * except it runs at page fault time instead of mmap time.
1854  *
1855  * This code used to be per-platform pmap_prefault().  It is now
1856  * machine-independent and enhanced to also pre-fault zero-fill pages
1857  * (see vm.fast_fault) as well as make them writable, which greatly
1858  * reduces the number of page faults programs incur.
1859  *
1860  * Application performance when pre-faulting zero-fill pages is heavily
1861  * dependent on the application.  Very tiny applications like /bin/echo
1862  * lose a little performance while applications of any appreciable size
1863  * gain performance.  Prefaulting multiple pages also reduces SMP
1864  * congestion and can improve SMP performance significantly.
1865  *
1866  * NOTE!  prot may allow writing but this only applies to the top level
1867  *        object.  If we wind up mapping a page extracted from a backing
1868  *        object we have to make sure it is read-only.
1869  *
1870  * NOTE!  The caller has already handled any COW operations on the
1871  *        vm_map_entry via the normal fault code.  Do NOT call this
1872  *        shortcut unless the normal fault code has run on this entry.
1873  */
1874 #define PFBAK 4
1875 #define PFFOR 4
1876 #define PAGEORDER_SIZE (PFBAK+PFFOR)
1877
1878 static int vm_prefault_pageorder[] = {
1879         -PAGE_SIZE, PAGE_SIZE,
1880         -2 * PAGE_SIZE, 2 * PAGE_SIZE,
1881         -3 * PAGE_SIZE, 3 * PAGE_SIZE,
1882         -4 * PAGE_SIZE, 4 * PAGE_SIZE
1883 };
1884
1885 static void
1886 vm_prefault(pmap_t pmap, vm_offset_t addra, vm_map_entry_t entry, int prot)
1887 {
1888         struct lwp *lp;
1889         vm_page_t m;
1890         vm_offset_t starta;
1891         vm_offset_t addr;
1892         vm_pindex_t index;
1893         vm_pindex_t pindex;
1894         vm_object_t object;
1895         int pprot;
1896         int i;
1897
1898         /*
1899          * We do not currently prefault mappings that use virtual page
1900          * tables.  We do not prefault foreign pmaps.
1901          */
1902         if (entry->maptype == VM_MAPTYPE_VPAGETABLE)
1903                 return;
1904         lp = curthread->td_lwp;
1905         if (lp == NULL || (pmap != vmspace_pmap(lp->lwp_vmspace)))
1906                 return;
1907
1908         object = entry->object.vm_object;
1909
1910         starta = addra - PFBAK * PAGE_SIZE;
1911         if (starta < entry->start)
1912                 starta = entry->start;
1913         else if (starta > addra)
1914                 starta = 0;
1915
1916         /*
1917          * critical section protection is required to maintain the
1918          * page/object association, interrupts can free pages and remove
1919          * them from their objects.
1920          */
1921         crit_enter();
1922         for (i = 0; i < PAGEORDER_SIZE; i++) {
1923                 vm_object_t lobject;
1924                 int allocated = 0;
1925
1926                 addr = addra + vm_prefault_pageorder[i];
1927                 if (addr > addra + (PFFOR * PAGE_SIZE))
1928                         addr = 0;
1929
1930                 if (addr < starta || addr >= entry->end)
1931                         continue;
1932
1933                 if (pmap_prefault_ok(pmap, addr) == 0)
1934                         continue;
1935
1936                 /*
1937                  * Follow the VM object chain to obtain the page to be mapped
1938                  * into the pmap.
1939                  *
1940                  * If we reach the terminal object without finding a page
1941                  * and we determine it would be advantageous, then allocate
1942                  * a zero-fill page for the base object.  The base object
1943                  * is guaranteed to be OBJT_DEFAULT for this case.
1944                  *
1945                  * In order to not have to check the pager via *haspage*()
1946                  * we stop if any non-default object is encountered.  e.g.
1947                  * a vnode or swap object would stop the loop.
1948                  */
1949                 index = ((addr - entry->start) + entry->offset) >> PAGE_SHIFT;
1950                 lobject = object;
1951                 pindex = index;
1952                 pprot = prot;
1953
1954                 while ((m = vm_page_lookup(lobject, pindex)) == NULL) {
1955                         if (lobject->type != OBJT_DEFAULT)
1956                                 break;
1957                         if (lobject->backing_object == NULL) {
1958                                 if (vm_fast_fault == 0)
1959                                         break;
1960                                 if (vm_prefault_pageorder[i] < 0 ||
1961                                     (prot & VM_PROT_WRITE) == 0 ||
1962                                     vm_page_count_min(0)) {
1963                                         break;
1964                                 }
1965                                 /* note: allocate from base object */
1966                                 m = vm_page_alloc(object, index,
1967                                               VM_ALLOC_NORMAL | VM_ALLOC_ZERO);
1968
1969                                 if ((m->flags & PG_ZERO) == 0) {
1970                                         vm_page_zero_fill(m);
1971                                 } else {
1972                                         vm_page_flag_clear(m, PG_ZERO);
1973                                         mycpu->gd_cnt.v_ozfod++;
1974                                 }
1975                                 mycpu->gd_cnt.v_zfod++;
1976                                 m->valid = VM_PAGE_BITS_ALL;
1977                                 allocated = 1;
1978                                 pprot = prot;
1979                                 /* lobject = object .. not needed */
1980                                 break;
1981                         }
1982                         if (lobject->backing_object_offset & PAGE_MASK)
1983                                 break;
1984                         pindex += lobject->backing_object_offset >> PAGE_SHIFT;
1985                         lobject = lobject->backing_object;
1986                         pprot &= ~VM_PROT_WRITE;
1987                 }
1988                 /*
1989                  * NOTE: lobject now invalid (if we did a zero-fill we didn't
1990                  *       bother assigning lobject = object).
1991                  *
1992                  * Give-up if the page is not available.
1993                  */
1994                 if (m == NULL)
1995                         break;
1996
1997                 /*
1998                  * Do not conditionalize on PG_RAM.  If pages are present in
1999                  * the VM system we assume optimal caching.  If caching is
2000                  * not optimal the I/O gravy train will be restarted when we
2001                  * hit an unavailable page.  We do not want to try to restart
2002                  * the gravy train now because we really don't know how much
2003                  * of the object has been cached.  The cost for restarting
2004                  * the gravy train should be low (since accesses will likely
2005                  * be I/O bound anyway).
2006                  *
2007                  * The object must be marked dirty if we are mapping a
2008                  * writable page.
2009                  */
2010                 if (pprot & VM_PROT_WRITE)
2011                         vm_object_set_writeable_dirty(m->object);
2012
2013                 /*
2014                  * Enter the page into the pmap if appropriate.  If we had
2015                  * allocated the page we have to place it on a queue.  If not
2016                  * we just have to make sure it isn't on the cache queue
2017                  * (pages on the cache queue are not allowed to be mapped).
2018                  */
2019                 if (allocated) {
2020                         pmap_enter(pmap, addr, m, pprot, 0);
2021                         vm_page_deactivate(m);
2022                         vm_page_wakeup(m);
2023                 } else if (((m->valid & VM_PAGE_BITS_ALL) == VM_PAGE_BITS_ALL) &&
2024                     (m->busy == 0) &&
2025                     (m->flags & (PG_BUSY | PG_FICTITIOUS)) == 0) {
2026
2027                         if ((m->queue - m->pc) == PQ_CACHE) {
2028                                 vm_page_deactivate(m);
2029                         }
2030                         vm_page_busy(m);
2031                         pmap_enter(pmap, addr, m, pprot, 0);
2032                         vm_page_wakeup(m);
2033                 }
2034         }
2035         crit_exit();
2036 }