xref: /dragonfly/sys/vm/vm_page.h (revision 4e7eb5cc)
1 /*
2  * Copyright (c) 1991, 1993
3  *	The Regents of the University of California.  All rights reserved.
4  *
5  * This code is derived from software contributed to Berkeley by
6  * The Mach Operating System project at Carnegie-Mellon University.
7  *
8  * Redistribution and use in source and binary forms, with or without
9  * modification, are permitted provided that the following conditions
10  * are met:
11  * 1. Redistributions of source code must retain the above copyright
12  *    notice, this list of conditions and the following disclaimer.
13  * 2. Redistributions in binary form must reproduce the above copyright
14  *    notice, this list of conditions and the following disclaimer in the
15  *    documentation and/or other materials provided with the distribution.
16  * 3. All advertising materials mentioning features or use of this software
17  *    must display the following acknowledgement:
18  *	This product includes software developed by the University of
19  *	California, Berkeley and its contributors.
20  * 4. Neither the name of the University nor the names of its contributors
21  *    may be used to endorse or promote products derived from this software
22  *    without specific prior written permission.
23  *
24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34  * SUCH DAMAGE.
35  *
36  *	from: @(#)vm_page.h	8.2 (Berkeley) 12/13/93
37  *
38  *
39  * Copyright (c) 1987, 1990 Carnegie-Mellon University.
40  * All rights reserved.
41  *
42  * Authors: Avadis Tevanian, Jr., Michael Wayne Young
43  *
44  * Permission to use, copy, modify and distribute this software and
45  * its documentation is hereby granted, provided that both the copyright
46  * notice and this permission notice appear in all copies of the
47  * software, derivative works or modified versions, and any portions
48  * thereof, and that both notices appear in supporting documentation.
49  *
50  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
51  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
52  * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
53  *
54  * Carnegie Mellon requests users of this software to return to
55  *
56  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
57  *  School of Computer Science
58  *  Carnegie Mellon University
59  *  Pittsburgh PA 15213-3890
60  *
61  * any improvements or extensions that they make and grant Carnegie the
62  * rights to redistribute these changes.
63  *
64  * $FreeBSD: src/sys/vm/vm_page.h,v 1.75.2.8 2002/03/06 01:07:09 dillon Exp $
65  * $DragonFly: src/sys/vm/vm_page.h,v 1.9 2004/01/20 05:04:08 dillon Exp $
66  */
67 
68 /*
69  *	Resident memory system definitions.
70  */
71 
72 #ifndef	_VM_PAGE_
73 #define	_VM_PAGE_
74 
75 #if !defined(KLD_MODULE)
76 #include "opt_vmpage.h"
77 #endif
78 
79 #include <vm/pmap.h>
80 #include <machine/atomic.h>
81 
82 /*
83  *	Management of resident (logical) pages.
84  *
85  *	A small structure is kept for each resident
86  *	page, indexed by page number.  Each structure
87  *	is an element of several lists:
88  *
89  *		A hash table bucket used to quickly
90  *		perform object/offset lookups
91  *
92  *		A list of all pages for a given object,
93  *		so they can be quickly deactivated at
94  *		time of deallocation.
95  *
96  *		An ordered list of pages due for pageout.
97  *
98  *	In addition, the structure contains the object
99  *	and offset to which this page belongs (for pageout),
100  *	and sundry status bits.
101  *
102  *	Fields in this structure are locked either by the lock on the
103  *	object that the page belongs to (O) or by the lock on the page
104  *	queues (P).
105  *
106  *	The 'valid' and 'dirty' fields are distinct.  A page may have dirty
107  *	bits set without having associated valid bits set.  This is used by
108  *	NFS to implement piecemeal writes.
109  */
110 
111 TAILQ_HEAD(pglist, vm_page);
112 
113 struct vm_page {
114 	TAILQ_ENTRY(vm_page) pageq;	/* queue info for FIFO queue or free list (P) */
115 	struct vm_page	*hnext;		/* hash table link (O,P)	*/
116 	TAILQ_ENTRY(vm_page) listq;	/* pages in same object (O) 	*/
117 
118 	vm_object_t object;		/* which object am I in (O,P)*/
119 	vm_pindex_t pindex;		/* offset into object (O,P) */
120 	vm_paddr_t phys_addr;		/* physical address of page */
121 	struct md_page md;		/* machine dependant stuff */
122 	u_short	queue;			/* page queue index */
123 	u_short	flags,			/* see below */
124 		pc;			/* page color */
125 	u_short wire_count;		/* wired down maps refs (P) */
126 	short hold_count;		/* page hold count */
127 	u_char	act_count;		/* page usage count */
128 	u_char	busy;			/* page busy count */
129 	/* NOTE that these must support one bit per DEV_BSIZE in a page!!! */
130 	/* so, on normal X86 kernels, they must be at least 8 bits wide */
131 #if PAGE_SIZE == 4096
132 	u_char	valid;			/* map of valid DEV_BSIZE chunks */
133 	u_char	dirty;			/* map of dirty DEV_BSIZE chunks */
134 #elif PAGE_SIZE == 8192
135 	u_short	valid;			/* map of valid DEV_BSIZE chunks */
136 	u_short	dirty;			/* map of dirty DEV_BSIZE chunks */
137 #endif
138 };
139 
140 /*
141  * note: currently use SWAPBLK_NONE as an absolute value rather then
142  * a flag bit.
143  */
144 
145 #define SWAPBLK_MASK	((daddr_t)((u_daddr_t)-1 >> 1))		/* mask */
146 #define SWAPBLK_NONE	((daddr_t)((u_daddr_t)SWAPBLK_MASK + 1))/* flag */
147 
148 #if !defined(KLD_MODULE)
149 
150 /*
151  * Page coloring parameters
152  */
153 /* Each of PQ_FREE, and PQ_CACHE have PQ_HASH_SIZE entries */
154 
155 /* Backward compatibility for existing PQ_*CACHE config options. */
156 #if !defined(PQ_CACHESIZE)
157 #if defined(PQ_HUGECACHE)
158 #define PQ_CACHESIZE 1024
159 #elif defined(PQ_LARGECACHE)
160 #define PQ_CACHESIZE 512
161 #elif defined(PQ_MEDIUMCACHE)
162 #define PQ_CACHESIZE 256
163 #elif defined(PQ_NORMALCACHE)
164 #define PQ_CACHESIZE 64
165 #elif defined(PQ_NOOPT)
166 #define PQ_CACHESIZE 0
167 #else
168 #define PQ_CACHESIZE 128
169 #endif
170 #endif
171 
172 #if PQ_CACHESIZE >= 1024
173 #define PQ_PRIME1 31	/* Prime number somewhat less than PQ_HASH_SIZE */
174 #define PQ_PRIME2 23	/* Prime number somewhat less than PQ_HASH_SIZE */
175 #define PQ_L2_SIZE 256	/* A number of colors opt for 1M cache */
176 
177 #elif PQ_CACHESIZE >= 512
178 #define PQ_PRIME1 31	/* Prime number somewhat less than PQ_HASH_SIZE */
179 #define PQ_PRIME2 23	/* Prime number somewhat less than PQ_HASH_SIZE */
180 #define PQ_L2_SIZE 128	/* A number of colors opt for 512K cache */
181 
182 #elif PQ_CACHESIZE >= 256
183 #define PQ_PRIME1 13	/* Prime number somewhat less than PQ_HASH_SIZE */
184 #define PQ_PRIME2 7	/* Prime number somewhat less than PQ_HASH_SIZE */
185 #define PQ_L2_SIZE 64	/* A number of colors opt for 256K cache */
186 
187 #elif PQ_CACHESIZE >= 128
188 #define PQ_PRIME1 9	/* Produces a good PQ_L2_SIZE/3 + PQ_PRIME1 */
189 #define PQ_PRIME2 5	/* Prime number somewhat less than PQ_HASH_SIZE */
190 #define PQ_L2_SIZE 32	/* A number of colors opt for 128k cache */
191 
192 #elif PQ_CACHESIZE >= 64
193 #define PQ_PRIME1 5	/* Prime number somewhat less than PQ_HASH_SIZE */
194 #define PQ_PRIME2 3	/* Prime number somewhat less than PQ_HASH_SIZE */
195 #define PQ_L2_SIZE 16	/* A reasonable number of colors (opt for 64K cache) */
196 
197 #else
198 #define PQ_PRIME1 1	/* Disable page coloring. */
199 #define PQ_PRIME2 1
200 #define PQ_L2_SIZE 1
201 
202 #endif
203 
204 #define PQ_L2_MASK (PQ_L2_SIZE - 1)
205 
206 #define PQ_NONE 0
207 #define PQ_FREE	1
208 #define PQ_INACTIVE (1 + 1*PQ_L2_SIZE)
209 #define PQ_ACTIVE (2 + 1*PQ_L2_SIZE)
210 #define PQ_CACHE (3 + 1*PQ_L2_SIZE)
211 #define PQ_HOLD  (3 + 2*PQ_L2_SIZE)
212 #define PQ_COUNT (4 + 2*PQ_L2_SIZE)
213 
214 struct vpgqueues {
215 	struct pglist pl;
216 	int	*cnt;
217 	int	lcnt;
218 	int	flipflop;	/* probably not the best place */
219 };
220 
221 extern struct vpgqueues vm_page_queues[PQ_COUNT];
222 
223 #endif
224 
225 /*
226  * These are the flags defined for vm_page.
227  *
228  * Note: PG_FILLED and PG_DIRTY are added for the filesystems.
229  *
230  * Note: PG_UNMANAGED (used by OBJT_PHYS) indicates that the page is
231  * 	 not under PV management but otherwise should be treated as a
232  *	 normal page.  Pages not under PV management cannot be paged out
233  *	 via the object/vm_page_t because there is no knowledge of their
234  *	 pte mappings, nor can they be removed from their objects via
235  *	 the object, and such pages are also not on any PQ queue.
236  */
237 #define	PG_BUSY		0x0001		/* page is in transit (O) */
238 #define	PG_WANTED	0x0002		/* someone is waiting for page (O) */
239 #define PG_WINATCFLS	0x0004		/* flush dirty page on inactive q */
240 #define	PG_FICTITIOUS	0x0008		/* physical page doesn't exist (O) */
241 #define	PG_WRITEABLE	0x0010		/* page is mapped writeable */
242 #define PG_MAPPED	0x0020		/* page is mapped */
243 #define	PG_ZERO		0x0040		/* page is zeroed */
244 #define PG_REFERENCED	0x0080		/* page has been referenced */
245 #define PG_CLEANCHK	0x0100		/* page will be checked for cleaning */
246 #define PG_SWAPINPROG	0x0200		/* swap I/O in progress on page	     */
247 #define PG_NOSYNC	0x0400		/* do not collect for syncer */
248 #define PG_UNMANAGED	0x0800		/* No PV management for page */
249 #define PG_MARKER	0x1000		/* special queue marker page */
250 
251 /*
252  * Misc constants.
253  */
254 
255 #define ACT_DECLINE		1
256 #define ACT_ADVANCE		3
257 #define ACT_INIT		5
258 #define ACT_MAX			64
259 #define PFCLUSTER_BEHIND	3
260 #define PFCLUSTER_AHEAD		3
261 
262 #ifdef _KERNEL
263 /*
264  * Each pageable resident page falls into one of four lists:
265  *
266  *	free
267  *		Available for allocation now.
268  *
269  * The following are all LRU sorted:
270  *
271  *	cache
272  *		Almost available for allocation. Still in an
273  *		object, but clean and immediately freeable at
274  *		non-interrupt times.
275  *
276  *	inactive
277  *		Low activity, candidates for reclamation.
278  *		This is the list of pages that should be
279  *		paged out next.
280  *
281  *	active
282  *		Pages that are "active" i.e. they have been
283  *		recently referenced.
284  *
285  *	zero
286  *		Pages that are really free and have been pre-zeroed
287  *
288  */
289 
290 extern int vm_page_zero_count;
291 
292 extern vm_page_t vm_page_array;		/* First resident page in table */
293 extern int vm_page_array_size;		/* number of vm_page_t's */
294 extern long first_page;			/* first physical page number */
295 
296 #define VM_PAGE_TO_PHYS(entry)	((entry)->phys_addr)
297 
298 #define PHYS_TO_VM_PAGE(pa) \
299 		(&vm_page_array[atop(pa) - first_page ])
300 
301 /*
302  *	Functions implemented as macros
303  */
304 
305 static __inline void
306 vm_page_flag_set(vm_page_t m, unsigned int bits)
307 {
308 	atomic_set_short(&(m)->flags, bits);
309 }
310 
311 static __inline void
312 vm_page_flag_clear(vm_page_t m, unsigned int bits)
313 {
314 	atomic_clear_short(&(m)->flags, bits);
315 }
316 
317 #if 0
318 static __inline void
319 vm_page_assert_wait(vm_page_t m, int interruptible)
320 {
321 	vm_page_flag_set(m, PG_WANTED);
322 	assert_wait((int) m, interruptible);
323 }
324 #endif
325 
326 static __inline void
327 vm_page_busy(vm_page_t m)
328 {
329 	KASSERT((m->flags & PG_BUSY) == 0, ("vm_page_busy: page already busy!!!"));
330 	vm_page_flag_set(m, PG_BUSY);
331 }
332 
333 /*
334  *	vm_page_flash:
335  *
336  *	wakeup anyone waiting for the page.
337  */
338 
339 static __inline void
340 vm_page_flash(vm_page_t m)
341 {
342 	if (m->flags & PG_WANTED) {
343 		vm_page_flag_clear(m, PG_WANTED);
344 		wakeup(m);
345 	}
346 }
347 
348 /*
349  *	vm_page_wakeup:
350  *
351  *	clear the PG_BUSY flag and wakeup anyone waiting for the
352  *	page.
353  *
354  */
355 
356 static __inline void
357 vm_page_wakeup(vm_page_t m)
358 {
359 	KASSERT(m->flags & PG_BUSY, ("vm_page_wakeup: page not busy!!!"));
360 	vm_page_flag_clear(m, PG_BUSY);
361 	vm_page_flash(m);
362 }
363 
364 /*
365  *
366  *
367  */
368 
369 static __inline void
370 vm_page_io_start(vm_page_t m)
371 {
372 	atomic_add_char(&(m)->busy, 1);
373 }
374 
375 static __inline void
376 vm_page_io_finish(vm_page_t m)
377 {
378 	atomic_subtract_char(&m->busy, 1);
379 	if (m->busy == 0)
380 		vm_page_flash(m);
381 }
382 
383 
384 #if PAGE_SIZE == 4096
385 #define VM_PAGE_BITS_ALL 0xff
386 #endif
387 
388 #if PAGE_SIZE == 8192
389 #define VM_PAGE_BITS_ALL 0xffff
390 #endif
391 
392 /*
393  * Note: the code will always use nominally free pages from the free list
394  * before trying other flag-specified sources.
395  *
396  * At least one of VM_ALLOC_NORMAL|VM_ALLOC_SYSTEM|VM_ALLOC_INTERRUPT
397  * must be specified.  VM_ALLOC_RETRY may only be specified if VM_ALLOC_NORMAL
398  * is also specified.
399  */
400 #define VM_ALLOC_NORMAL		0x01	/* ok to use cache pages */
401 #define VM_ALLOC_SYSTEM		0x02	/* ok to exhaust most of free list */
402 #define VM_ALLOC_INTERRUPT	0x04	/* ok to exhaust entire free list */
403 #define	VM_ALLOC_ZERO		0x08	/* req pre-zero'd memory if avail */
404 #define	VM_ALLOC_RETRY		0x80	/* indefinite block (vm_page_grab()) */
405 
406 void vm_page_unhold(vm_page_t mem);
407 
408 void vm_page_activate (vm_page_t);
409 vm_page_t vm_page_alloc (vm_object_t, vm_pindex_t, int);
410 vm_page_t vm_page_grab (vm_object_t, vm_pindex_t, int);
411 void vm_page_cache (vm_page_t);
412 int vm_page_try_to_cache (vm_page_t);
413 int vm_page_try_to_free (vm_page_t);
414 void vm_page_dontneed (vm_page_t);
415 static __inline void vm_page_copy (vm_page_t, vm_page_t);
416 static __inline void vm_page_free (vm_page_t);
417 static __inline void vm_page_free_zero (vm_page_t);
418 void vm_page_deactivate (vm_page_t);
419 void vm_page_insert (vm_page_t, vm_object_t, vm_pindex_t);
420 vm_page_t vm_page_lookup (vm_object_t, vm_pindex_t);
421 void vm_page_remove (vm_page_t);
422 void vm_page_rename (vm_page_t, vm_object_t, vm_pindex_t);
423 vm_offset_t vm_page_startup (vm_offset_t, vm_offset_t, vm_offset_t);
424 vm_page_t vm_add_new_page (vm_paddr_t pa);
425 void vm_page_unmanage (vm_page_t);
426 void vm_page_unwire (vm_page_t, int);
427 void vm_page_wire (vm_page_t);
428 void vm_page_unqueue (vm_page_t);
429 void vm_page_unqueue_nowakeup (vm_page_t);
430 void vm_page_set_validclean (vm_page_t, int, int);
431 void vm_page_set_dirty (vm_page_t, int, int);
432 void vm_page_clear_dirty (vm_page_t, int, int);
433 void vm_page_set_invalid (vm_page_t, int, int);
434 static __inline boolean_t vm_page_zero_fill (vm_page_t);
435 int vm_page_is_valid (vm_page_t, int, int);
436 void vm_page_test_dirty (vm_page_t);
437 int vm_page_bits (int, int);
438 vm_page_t _vm_page_list_find (int, int);
439 void vm_page_zero_invalid(vm_page_t m, boolean_t setvalid);
440 void vm_page_free_toq(vm_page_t m);
441 
442 int vm_contig_pg_alloc(u_long, vm_paddr_t, vm_paddr_t, u_long, u_long);
443 vm_offset_t vm_contig_pg_kmap(int, u_long, vm_map_t);
444 void vm_contig_pg_free(int, u_long);
445 
446 /*
447  * Keep page from being freed by the page daemon
448  * much of the same effect as wiring, except much lower
449  * overhead and should be used only for *very* temporary
450  * holding ("wiring").
451  */
452 static __inline void
453 vm_page_hold(vm_page_t mem)
454 {
455 	mem->hold_count++;
456 }
457 
458 /*
459  * 	vm_page_protect:
460  *
461  *	Reduce the protection of a page.  This routine never raises the
462  *	protection and therefore can be safely called if the page is already
463  *	at VM_PROT_NONE (it will be a NOP effectively ).
464  */
465 
466 static __inline void
467 vm_page_protect(vm_page_t mem, int prot)
468 {
469 	if (prot == VM_PROT_NONE) {
470 		if (mem->flags & (PG_WRITEABLE|PG_MAPPED)) {
471 			pmap_page_protect(mem, VM_PROT_NONE);
472 			vm_page_flag_clear(mem, PG_WRITEABLE|PG_MAPPED);
473 		}
474 	} else if ((prot == VM_PROT_READ) && (mem->flags & PG_WRITEABLE)) {
475 		pmap_page_protect(mem, VM_PROT_READ);
476 		vm_page_flag_clear(mem, PG_WRITEABLE);
477 	}
478 }
479 
480 /*
481  *	vm_page_zero_fill:
482  *
483  *	Zero-fill the specified page.
484  *	Written as a standard pagein routine, to
485  *	be used by the zero-fill object.
486  */
487 static __inline boolean_t
488 vm_page_zero_fill(m)
489 	vm_page_t m;
490 {
491 	pmap_zero_page(VM_PAGE_TO_PHYS(m));
492 	return (TRUE);
493 }
494 
495 /*
496  *	vm_page_copy:
497  *
498  *	Copy one page to another
499  */
500 static __inline void
501 vm_page_copy(src_m, dest_m)
502 	vm_page_t src_m;
503 	vm_page_t dest_m;
504 {
505 	pmap_copy_page(VM_PAGE_TO_PHYS(src_m), VM_PAGE_TO_PHYS(dest_m));
506 	dest_m->valid = VM_PAGE_BITS_ALL;
507 }
508 
509 /*
510  *	vm_page_free:
511  *
512  *	Free a page
513  *
514  *	The clearing of PG_ZERO is a temporary safety until the code can be
515  *	reviewed to determine that PG_ZERO is being properly cleared on
516  *	write faults or maps.  PG_ZERO was previously cleared in
517  *	vm_page_alloc().
518  */
519 static __inline void
520 vm_page_free(m)
521 	vm_page_t m;
522 {
523 	vm_page_flag_clear(m, PG_ZERO);
524 	vm_page_free_toq(m);
525 }
526 
527 /*
528  *	vm_page_free_zero:
529  *
530  *	Free a page to the zerod-pages queue
531  */
532 static __inline void
533 vm_page_free_zero(m)
534 	vm_page_t m;
535 {
536 	vm_page_flag_set(m, PG_ZERO);
537 	vm_page_free_toq(m);
538 }
539 
540 /*
541  *	vm_page_sleep_busy:
542  *
543  *	Wait until page is no longer PG_BUSY or (if also_m_busy is TRUE)
544  *	m->busy is zero.  Returns TRUE if it had to sleep ( including if
545  *	it almost had to sleep and made temporary spl*() mods), FALSE
546  *	otherwise.
547  *
548  *	This routine assumes that interrupts can only remove the busy
549  *	status from a page, not set the busy status or change it from
550  *	PG_BUSY to m->busy or vise versa (which would create a timing
551  *	window).
552  *
553  *	Note that being an inline, this code will be well optimized.
554  */
555 
556 static __inline int
557 vm_page_sleep_busy(vm_page_t m, int also_m_busy, const char *msg)
558 {
559 	if ((m->flags & PG_BUSY) || (also_m_busy && m->busy))  {
560 		int s = splvm();
561 		if ((m->flags & PG_BUSY) || (also_m_busy && m->busy)) {
562 			/*
563 			 * Page is busy. Wait and retry.
564 			 */
565 			vm_page_flag_set(m, PG_WANTED | PG_REFERENCED);
566 			tsleep(m, 0, msg, 0);
567 		}
568 		splx(s);
569 		return(TRUE);
570 		/* not reached */
571 	}
572 	return(FALSE);
573 }
574 
575 /*
576  *	vm_page_dirty:
577  *
578  *	make page all dirty
579  */
580 
581 static __inline void
582 vm_page_dirty(vm_page_t m)
583 {
584 #if !defined(KLD_MODULE)
585 	KASSERT(m->queue - m->pc != PQ_CACHE, ("vm_page_dirty: page in cache!"));
586 #endif
587 	m->dirty = VM_PAGE_BITS_ALL;
588 }
589 
590 /*
591  *	vm_page_undirty:
592  *
593  *	Set page to not be dirty.  Note: does not clear pmap modify bits
594  */
595 
596 static __inline void
597 vm_page_undirty(vm_page_t m)
598 {
599 	m->dirty = 0;
600 }
601 
602 #if !defined(KLD_MODULE)
603 
604 static __inline vm_page_t
605 vm_page_list_find(int basequeue, int index, boolean_t prefer_zero)
606 {
607 	vm_page_t m;
608 
609 #if PQ_L2_SIZE > 1
610 	if (prefer_zero) {
611 		m = TAILQ_LAST(&vm_page_queues[basequeue+index].pl, pglist);
612 	} else {
613 		m = TAILQ_FIRST(&vm_page_queues[basequeue+index].pl);
614 	}
615 	if (m == NULL)
616 		m = _vm_page_list_find(basequeue, index);
617 #else
618 	if (prefer_zero) {
619 		m = TAILQ_LAST(&vm_page_queues[basequeue].pl, pglist);
620 	} else {
621 		m = TAILQ_FIRST(&vm_page_queues[basequeue].pl);
622 	}
623 #endif
624 	return(m);
625 }
626 
627 #endif
628 
629 #endif				/* _KERNEL */
630 #endif				/* !_VM_PAGE_ */
631