The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/vm/vm_pager.c

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    1 /*-
    2  * SPDX-License-Identifier: (BSD-3-Clause AND MIT-CMU)
    3  *
    4  * Copyright (c) 1991, 1993
    5  *      The Regents of the University of California.  All rights reserved.
    6  *
    7  * This code is derived from software contributed to Berkeley by
    8  * The Mach Operating System project at Carnegie-Mellon University.
    9  *
   10  * Redistribution and use in source and binary forms, with or without
   11  * modification, are permitted provided that the following conditions
   12  * are met:
   13  * 1. Redistributions of source code must retain the above copyright
   14  *    notice, this list of conditions and the following disclaimer.
   15  * 2. Redistributions in binary form must reproduce the above copyright
   16  *    notice, this list of conditions and the following disclaimer in the
   17  *    documentation and/or other materials provided with the distribution.
   18  * 3. Neither the name of the University nor the names of its contributors
   19  *    may be used to endorse or promote products derived from this software
   20  *    without specific prior written permission.
   21  *
   22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   32  * SUCH DAMAGE.
   33  *
   34  *      from: @(#)vm_pager.c    8.6 (Berkeley) 1/12/94
   35  *
   36  *
   37  * Copyright (c) 1987, 1990 Carnegie-Mellon University.
   38  * All rights reserved.
   39  *
   40  * Authors: Avadis Tevanian, Jr., Michael Wayne Young
   41  *
   42  * Permission to use, copy, modify and distribute this software and
   43  * its documentation is hereby granted, provided that both the copyright
   44  * notice and this permission notice appear in all copies of the
   45  * software, derivative works or modified versions, and any portions
   46  * thereof, and that both notices appear in supporting documentation.
   47  *
   48  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
   49  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
   50  * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
   51  *
   52  * Carnegie Mellon requests users of this software to return to
   53  *
   54  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
   55  *  School of Computer Science
   56  *  Carnegie Mellon University
   57  *  Pittsburgh PA 15213-3890
   58  *
   59  * any improvements or extensions that they make and grant Carnegie the
   60  * rights to redistribute these changes.
   61  */
   62 
   63 /*
   64  *      Paging space routine stubs.  Emulates a matchmaker-like interface
   65  *      for builtin pagers.
   66  */
   67 
   68 #include <sys/cdefs.h>
   69 __FBSDID("$FreeBSD$");
   70 
   71 #include <sys/param.h>
   72 #include <sys/systm.h>
   73 #include <sys/kernel.h>
   74 #include <sys/vnode.h>
   75 #include <sys/bio.h>
   76 #include <sys/buf.h>
   77 #include <sys/ucred.h>
   78 #include <sys/malloc.h>
   79 #include <sys/rwlock.h>
   80 
   81 #include <vm/vm.h>
   82 #include <vm/vm_param.h>
   83 #include <vm/vm_kern.h>
   84 #include <vm/vm_object.h>
   85 #include <vm/vm_page.h>
   86 #include <vm/vm_pager.h>
   87 #include <vm/vm_extern.h>
   88 
   89 int cluster_pbuf_freecnt = -1;  /* unlimited to begin with */
   90 
   91 struct buf *swbuf;
   92 
   93 static int dead_pager_getpages(vm_object_t, vm_page_t *, int, int *, int *);
   94 static vm_object_t dead_pager_alloc(void *, vm_ooffset_t, vm_prot_t,
   95     vm_ooffset_t, struct ucred *);
   96 static void dead_pager_putpages(vm_object_t, vm_page_t *, int, int, int *);
   97 static boolean_t dead_pager_haspage(vm_object_t, vm_pindex_t, int *, int *);
   98 static void dead_pager_dealloc(vm_object_t);
   99 
  100 static int
  101 dead_pager_getpages(vm_object_t obj, vm_page_t *ma, int count, int *rbehind,
  102     int *rahead)
  103 {
  104 
  105         return (VM_PAGER_FAIL);
  106 }
  107 
  108 static vm_object_t
  109 dead_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
  110     vm_ooffset_t off, struct ucred *cred)
  111 {
  112 
  113         return (NULL);
  114 }
  115 
  116 static void
  117 dead_pager_putpages(vm_object_t object, vm_page_t *m, int count,
  118     int flags, int *rtvals)
  119 {
  120         int i;
  121 
  122         for (i = 0; i < count; i++)
  123                 rtvals[i] = VM_PAGER_AGAIN;
  124 }
  125 
  126 static int
  127 dead_pager_haspage(vm_object_t object, vm_pindex_t pindex, int *prev, int *next)
  128 {
  129 
  130         if (prev != NULL)
  131                 *prev = 0;
  132         if (next != NULL)
  133                 *next = 0;
  134         return (FALSE);
  135 }
  136 
  137 static void
  138 dead_pager_dealloc(vm_object_t object)
  139 {
  140 
  141 }
  142 
  143 static struct pagerops deadpagerops = {
  144         .pgo_alloc =    dead_pager_alloc,
  145         .pgo_dealloc =  dead_pager_dealloc,
  146         .pgo_getpages = dead_pager_getpages,
  147         .pgo_putpages = dead_pager_putpages,
  148         .pgo_haspage =  dead_pager_haspage,
  149 };
  150 
  151 struct pagerops *pagertab[] = {
  152         &defaultpagerops,       /* OBJT_DEFAULT */
  153         &swappagerops,          /* OBJT_SWAP */
  154         &vnodepagerops,         /* OBJT_VNODE */
  155         &devicepagerops,        /* OBJT_DEVICE */
  156         &physpagerops,          /* OBJT_PHYS */
  157         &deadpagerops,          /* OBJT_DEAD */
  158         &sgpagerops,            /* OBJT_SG */
  159         &mgtdevicepagerops,     /* OBJT_MGTDEVICE */
  160 };
  161 
  162 /*
  163  * Kernel address space for mapping pages.
  164  * Used by pagers where KVAs are needed for IO.
  165  *
  166  * XXX needs to be large enough to support the number of pending async
  167  * cleaning requests (NPENDINGIO == 64) * the maximum swap cluster size
  168  * (MAXPHYS == 64k) if you want to get the most efficiency.
  169  */
  170 struct mtx_padalign __exclusive_cache_line pbuf_mtx;
  171 static TAILQ_HEAD(swqueue, buf) bswlist;
  172 static int bswneeded;
  173 vm_offset_t swapbkva;           /* swap buffers kva */
  174 
  175 void
  176 vm_pager_init(void)
  177 {
  178         struct pagerops **pgops;
  179 
  180         TAILQ_INIT(&bswlist);
  181         /*
  182          * Initialize known pagers
  183          */
  184         for (pgops = pagertab; pgops < &pagertab[nitems(pagertab)]; pgops++)
  185                 if ((*pgops)->pgo_init != NULL)
  186                         (*(*pgops)->pgo_init)();
  187 }
  188 
  189 void
  190 vm_pager_bufferinit(void)
  191 {
  192         struct buf *bp;
  193         int i;
  194 
  195         mtx_init(&pbuf_mtx, "pbuf mutex", NULL, MTX_DEF);
  196         bp = swbuf;
  197         /*
  198          * Now set up swap and physical I/O buffer headers.
  199          */
  200         for (i = 0; i < nswbuf; i++, bp++) {
  201                 TAILQ_INSERT_HEAD(&bswlist, bp, b_freelist);
  202                 BUF_LOCKINIT(bp);
  203                 LIST_INIT(&bp->b_dep);
  204                 bp->b_rcred = bp->b_wcred = NOCRED;
  205                 bp->b_xflags = 0;
  206         }
  207 
  208         cluster_pbuf_freecnt = nswbuf / 2;
  209         vnode_pbuf_freecnt = nswbuf / 2 + 1;
  210         vnode_async_pbuf_freecnt = nswbuf / 2;
  211 }
  212 
  213 /*
  214  * Allocate an instance of a pager of the given type.
  215  * Size, protection and offset parameters are passed in for pagers that
  216  * need to perform page-level validation (e.g. the device pager).
  217  */
  218 vm_object_t
  219 vm_pager_allocate(objtype_t type, void *handle, vm_ooffset_t size,
  220     vm_prot_t prot, vm_ooffset_t off, struct ucred *cred)
  221 {
  222         vm_object_t ret;
  223         struct pagerops *ops;
  224 
  225         ops = pagertab[type];
  226         if (ops)
  227                 ret = (*ops->pgo_alloc)(handle, size, prot, off, cred);
  228         else
  229                 ret = NULL;
  230         return (ret);
  231 }
  232 
  233 /*
  234  *      The object must be locked.
  235  */
  236 void
  237 vm_pager_deallocate(vm_object_t object)
  238 {
  239 
  240         VM_OBJECT_ASSERT_WLOCKED(object);
  241         (*pagertab[object->type]->pgo_dealloc) (object);
  242 }
  243 
  244 static void
  245 vm_pager_assert_in(vm_object_t object, vm_page_t *m, int count)
  246 {
  247 #ifdef INVARIANTS
  248 
  249         VM_OBJECT_ASSERT_WLOCKED(object);
  250         KASSERT(count > 0, ("%s: 0 count", __func__));
  251         /*
  252          * All pages must be busied, not mapped, not fully valid,
  253          * not dirty and belong to the proper object.
  254          */
  255         for (int i = 0 ; i < count; i++) {
  256                 if (m[i] == bogus_page)
  257                         continue;
  258                 vm_page_assert_xbusied(m[i]);
  259                 KASSERT(!pmap_page_is_mapped(m[i]),
  260                     ("%s: page %p is mapped", __func__, m[i]));
  261                 KASSERT(m[i]->valid != VM_PAGE_BITS_ALL,
  262                     ("%s: request for a valid page %p", __func__, m[i]));
  263                 KASSERT(m[i]->dirty == 0,
  264                     ("%s: page %p is dirty", __func__, m[i]));
  265                 KASSERT(m[i]->object == object,
  266                     ("%s: wrong object %p/%p", __func__, object, m[i]->object));
  267         }
  268 #endif
  269 }
  270 
  271 /*
  272  * Page in the pages for the object using its associated pager.
  273  * The requested page must be fully valid on successful return.
  274  */
  275 int
  276 vm_pager_get_pages(vm_object_t object, vm_page_t *m, int count, int *rbehind,
  277     int *rahead)
  278 {
  279 #ifdef INVARIANTS
  280         vm_pindex_t pindex = m[0]->pindex;
  281 #endif
  282         int r;
  283 
  284         vm_pager_assert_in(object, m, count);
  285 
  286         r = (*pagertab[object->type]->pgo_getpages)(object, m, count, rbehind,
  287             rahead);
  288         if (r != VM_PAGER_OK)
  289                 return (r);
  290 
  291         for (int i = 0; i < count; i++) {
  292                 /*
  293                  * If pager has replaced a page, assert that it had
  294                  * updated the array.
  295                  */
  296                 KASSERT(m[i] == vm_page_lookup(object, pindex++),
  297                     ("%s: mismatch page %p pindex %ju", __func__,
  298                     m[i], (uintmax_t )pindex - 1));
  299                 /*
  300                  * Zero out partially filled data.
  301                  */
  302                 if (m[i]->valid != VM_PAGE_BITS_ALL)
  303                         vm_page_zero_invalid(m[i], TRUE);
  304         }
  305         return (VM_PAGER_OK);
  306 }
  307 
  308 int
  309 vm_pager_get_pages_async(vm_object_t object, vm_page_t *m, int count,
  310     int *rbehind, int *rahead, pgo_getpages_iodone_t iodone, void *arg)
  311 {
  312 
  313         vm_pager_assert_in(object, m, count);
  314 
  315         return ((*pagertab[object->type]->pgo_getpages_async)(object, m,
  316             count, rbehind, rahead, iodone, arg));
  317 }
  318 
  319 /*
  320  * vm_pager_put_pages() - inline, see vm/vm_pager.h
  321  * vm_pager_has_page() - inline, see vm/vm_pager.h
  322  */
  323 
  324 /*
  325  * Search the specified pager object list for an object with the
  326  * specified handle.  If an object with the specified handle is found,
  327  * increase its reference count and return it.  Otherwise, return NULL.
  328  *
  329  * The pager object list must be locked.
  330  */
  331 vm_object_t
  332 vm_pager_object_lookup(struct pagerlst *pg_list, void *handle)
  333 {
  334         vm_object_t object;
  335 
  336         TAILQ_FOREACH(object, pg_list, pager_object_list) {
  337                 if (object->handle == handle) {
  338                         VM_OBJECT_WLOCK(object);
  339                         if ((object->flags & OBJ_DEAD) == 0) {
  340                                 vm_object_reference_locked(object);
  341                                 VM_OBJECT_WUNLOCK(object);
  342                                 break;
  343                         }
  344                         VM_OBJECT_WUNLOCK(object);
  345                 }
  346         }
  347         return (object);
  348 }
  349 
  350 /*
  351  * initialize a physical buffer
  352  */
  353 
  354 /*
  355  * XXX This probably belongs in vfs_bio.c
  356  */
  357 static void
  358 initpbuf(struct buf *bp)
  359 {
  360 
  361         KASSERT(bp->b_bufobj == NULL, ("initpbuf with bufobj"));
  362         KASSERT(bp->b_vp == NULL, ("initpbuf with vp"));
  363         bp->b_rcred = NOCRED;
  364         bp->b_wcred = NOCRED;
  365         bp->b_qindex = 0;       /* On no queue (QUEUE_NONE) */
  366         bp->b_kvabase = (caddr_t)(MAXPHYS * (bp - swbuf)) + swapbkva;
  367         bp->b_data = bp->b_kvabase;
  368         bp->b_kvasize = MAXPHYS;
  369         bp->b_flags = 0;
  370         bp->b_xflags = 0;
  371         bp->b_ioflags = 0;
  372         bp->b_iodone = NULL;
  373         bp->b_error = 0;
  374         BUF_LOCK(bp, LK_EXCLUSIVE, NULL);
  375         buf_track(bp, __func__);
  376 }
  377 
  378 /*
  379  * allocate a physical buffer
  380  *
  381  *      There are a limited number (nswbuf) of physical buffers.  We need
  382  *      to make sure that no single subsystem is able to hog all of them,
  383  *      so each subsystem implements a counter which is typically initialized
  384  *      to 1/2 nswbuf.  getpbuf() decrements this counter in allocation and
  385  *      increments it on release, and blocks if the counter hits zero.  A
  386  *      subsystem may initialize the counter to -1 to disable the feature,
  387  *      but it must still be sure to match up all uses of getpbuf() with 
  388  *      relpbuf() using the same variable.
  389  *
  390  *      NOTE: pfreecnt can be NULL, but this 'feature' will be removed
  391  *      relatively soon when the rest of the subsystems get smart about it. XXX
  392  */
  393 struct buf *
  394 getpbuf(int *pfreecnt)
  395 {
  396         struct buf *bp;
  397 
  398         mtx_lock(&pbuf_mtx);
  399         for (;;) {
  400                 if (pfreecnt != NULL) {
  401                         while (*pfreecnt == 0) {
  402                                 msleep(pfreecnt, &pbuf_mtx, PVM, "wswbuf0", 0);
  403                         }
  404                 }
  405 
  406                 /* get a bp from the swap buffer header pool */
  407                 if ((bp = TAILQ_FIRST(&bswlist)) != NULL)
  408                         break;
  409 
  410                 bswneeded = 1;
  411                 msleep(&bswneeded, &pbuf_mtx, PVM, "wswbuf1", 0);
  412                 /* loop in case someone else grabbed one */
  413         }
  414         TAILQ_REMOVE(&bswlist, bp, b_freelist);
  415         if (pfreecnt)
  416                 --*pfreecnt;
  417         mtx_unlock(&pbuf_mtx);
  418         initpbuf(bp);
  419         return (bp);
  420 }
  421 
  422 /*
  423  * allocate a physical buffer, if one is available.
  424  *
  425  *      Note that there is no NULL hack here - all subsystems using this
  426  *      call understand how to use pfreecnt.
  427  */
  428 struct buf *
  429 trypbuf(int *pfreecnt)
  430 {
  431         struct buf *bp;
  432 
  433         mtx_lock(&pbuf_mtx);
  434         if (*pfreecnt == 0 || (bp = TAILQ_FIRST(&bswlist)) == NULL) {
  435                 mtx_unlock(&pbuf_mtx);
  436                 return NULL;
  437         }
  438         TAILQ_REMOVE(&bswlist, bp, b_freelist);
  439         --*pfreecnt;
  440         mtx_unlock(&pbuf_mtx);
  441         initpbuf(bp);
  442         return (bp);
  443 }
  444 
  445 /*
  446  * release a physical buffer
  447  *
  448  *      NOTE: pfreecnt can be NULL, but this 'feature' will be removed
  449  *      relatively soon when the rest of the subsystems get smart about it. XXX
  450  */
  451 void
  452 relpbuf(struct buf *bp, int *pfreecnt)
  453 {
  454 
  455         if (bp->b_rcred != NOCRED) {
  456                 crfree(bp->b_rcred);
  457                 bp->b_rcred = NOCRED;
  458         }
  459         if (bp->b_wcred != NOCRED) {
  460                 crfree(bp->b_wcred);
  461                 bp->b_wcred = NOCRED;
  462         }
  463 
  464         KASSERT(bp->b_vp == NULL, ("relpbuf with vp"));
  465         KASSERT(bp->b_bufobj == NULL, ("relpbuf with bufobj"));
  466 
  467         buf_track(bp, __func__);
  468         BUF_UNLOCK(bp);
  469 
  470         mtx_lock(&pbuf_mtx);
  471         TAILQ_INSERT_HEAD(&bswlist, bp, b_freelist);
  472 
  473         if (bswneeded) {
  474                 bswneeded = 0;
  475                 wakeup(&bswneeded);
  476         }
  477         if (pfreecnt) {
  478                 if (++*pfreecnt == 1)
  479                         wakeup(pfreecnt);
  480         }
  481         mtx_unlock(&pbuf_mtx);
  482 }
  483 
  484 /*
  485  * Associate a p-buffer with a vnode.
  486  *
  487  * Also sets B_PAGING flag to indicate that vnode is not fully associated
  488  * with the buffer.  i.e. the bp has not been linked into the vnode or
  489  * ref-counted.
  490  */
  491 void
  492 pbgetvp(struct vnode *vp, struct buf *bp)
  493 {
  494 
  495         KASSERT(bp->b_vp == NULL, ("pbgetvp: not free"));
  496         KASSERT(bp->b_bufobj == NULL, ("pbgetvp: not free (bufobj)"));
  497 
  498         bp->b_vp = vp;
  499         bp->b_flags |= B_PAGING;
  500         bp->b_bufobj = &vp->v_bufobj;
  501 }
  502 
  503 /*
  504  * Associate a p-buffer with a vnode.
  505  *
  506  * Also sets B_PAGING flag to indicate that vnode is not fully associated
  507  * with the buffer.  i.e. the bp has not been linked into the vnode or
  508  * ref-counted.
  509  */
  510 void
  511 pbgetbo(struct bufobj *bo, struct buf *bp)
  512 {
  513 
  514         KASSERT(bp->b_vp == NULL, ("pbgetbo: not free (vnode)"));
  515         KASSERT(bp->b_bufobj == NULL, ("pbgetbo: not free (bufobj)"));
  516 
  517         bp->b_flags |= B_PAGING;
  518         bp->b_bufobj = bo;
  519 }
  520 
  521 /*
  522  * Disassociate a p-buffer from a vnode.
  523  */
  524 void
  525 pbrelvp(struct buf *bp)
  526 {
  527 
  528         KASSERT(bp->b_vp != NULL, ("pbrelvp: NULL"));
  529         KASSERT(bp->b_bufobj != NULL, ("pbrelvp: NULL bufobj"));
  530         KASSERT((bp->b_xflags & (BX_VNDIRTY | BX_VNCLEAN)) == 0,
  531             ("pbrelvp: pager buf on vnode list."));
  532 
  533         bp->b_vp = NULL;
  534         bp->b_bufobj = NULL;
  535         bp->b_flags &= ~B_PAGING;
  536 }
  537 
  538 /*
  539  * Disassociate a p-buffer from a bufobj.
  540  */
  541 void
  542 pbrelbo(struct buf *bp)
  543 {
  544 
  545         KASSERT(bp->b_vp == NULL, ("pbrelbo: vnode"));
  546         KASSERT(bp->b_bufobj != NULL, ("pbrelbo: NULL bufobj"));
  547         KASSERT((bp->b_xflags & (BX_VNDIRTY | BX_VNCLEAN)) == 0,
  548             ("pbrelbo: pager buf on vnode list."));
  549 
  550         bp->b_bufobj = NULL;
  551         bp->b_flags &= ~B_PAGING;
  552 }

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