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  * 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  * 4. Neither the name of the University nor the names of its contributors
   17  *    may be used to endorse or promote products derived from this software
   18  *    without specific prior written permission.
   19  *
   20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   30  * SUCH DAMAGE.
   31  *
   32  *      from: @(#)vm_pager.c    8.6 (Berkeley) 1/12/94
   33  *
   34  *
   35  * Copyright (c) 1987, 1990 Carnegie-Mellon University.
   36  * All rights reserved.
   37  *
   38  * Authors: Avadis Tevanian, Jr., Michael Wayne Young
   39  *
   40  * Permission to use, copy, modify and distribute this software and
   41  * its documentation is hereby granted, provided that both the copyright
   42  * notice and this permission notice appear in all copies of the
   43  * software, derivative works or modified versions, and any portions
   44  * thereof, and that both notices appear in supporting documentation.
   45  *
   46  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
   47  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
   48  * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
   49  *
   50  * Carnegie Mellon requests users of this software to return to
   51  *
   52  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
   53  *  School of Computer Science
   54  *  Carnegie Mellon University
   55  *  Pittsburgh PA 15213-3890
   56  *
   57  * any improvements or extensions that they make and grant Carnegie the
   58  * rights to redistribute these changes.
   59  */
   60 
   61 /*
   62  *      Paging space routine stubs.  Emulates a matchmaker-like interface
   63  *      for builtin pagers.
   64  */
   65 
   66 #include <sys/cdefs.h>
   67 __FBSDID("$FreeBSD: releng/10.4/sys/vm/vm_pager.c 311645 2017-01-07 12:04:30Z kib $");
   68 
   69 #include <sys/param.h>
   70 #include <sys/systm.h>
   71 #include <sys/kernel.h>
   72 #include <sys/vnode.h>
   73 #include <sys/bio.h>
   74 #include <sys/buf.h>
   75 #include <sys/ucred.h>
   76 #include <sys/malloc.h>
   77 #include <sys/rwlock.h>
   78 
   79 #include <vm/vm.h>
   80 #include <vm/vm_param.h>
   81 #include <vm/vm_kern.h>
   82 #include <vm/vm_object.h>
   83 #include <vm/vm_page.h>
   84 #include <vm/vm_pager.h>
   85 #include <vm/vm_extern.h>
   86 
   87 int cluster_pbuf_freecnt = -1;  /* unlimited to begin with */
   88 
   89 static int dead_pager_getpages(vm_object_t, vm_page_t *, int, int);
   90 static vm_object_t dead_pager_alloc(void *, vm_ooffset_t, vm_prot_t,
   91     vm_ooffset_t, struct ucred *);
   92 static void dead_pager_putpages(vm_object_t, vm_page_t *, int, int, int *);
   93 static boolean_t dead_pager_haspage(vm_object_t, vm_pindex_t, int *, int *);
   94 static void dead_pager_dealloc(vm_object_t);
   95 
   96 static int
   97 dead_pager_getpages(obj, ma, count, req)
   98         vm_object_t obj;
   99         vm_page_t *ma;
  100         int count;
  101         int req;
  102 {
  103         return VM_PAGER_FAIL;
  104 }
  105 
  106 static vm_object_t
  107 dead_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
  108     vm_ooffset_t off, struct ucred *cred)
  109 {
  110 
  111         return (NULL);
  112 }
  113 
  114 static void
  115 dead_pager_putpages(vm_object_t object, vm_page_t *m, int count,
  116     int flags, int *rtvals)
  117 {
  118         int i;
  119 
  120         for (i = 0; i < count; i++)
  121                 rtvals[i] = VM_PAGER_AGAIN;
  122 }
  123 
  124 static int
  125 dead_pager_haspage(vm_object_t object, vm_pindex_t pindex, int *prev, int *next)
  126 {
  127 
  128         if (prev != NULL)
  129                 *prev = 0;
  130         if (next != NULL)
  131                 *next = 0;
  132         return (FALSE);
  133 }
  134 
  135 static void
  136 dead_pager_dealloc(vm_object_t object)
  137 {
  138 
  139 }
  140 
  141 static struct pagerops deadpagerops = {
  142         .pgo_alloc =    dead_pager_alloc,
  143         .pgo_dealloc =  dead_pager_dealloc,
  144         .pgo_getpages = dead_pager_getpages,
  145         .pgo_putpages = dead_pager_putpages,
  146         .pgo_haspage =  dead_pager_haspage,
  147 };
  148 
  149 struct pagerops *pagertab[] = {
  150         &defaultpagerops,       /* OBJT_DEFAULT */
  151         &swappagerops,          /* OBJT_SWAP */
  152         &vnodepagerops,         /* OBJT_VNODE */
  153         &devicepagerops,        /* OBJT_DEVICE */
  154         &physpagerops,          /* OBJT_PHYS */
  155         &deadpagerops,          /* OBJT_DEAD */
  156         &sgpagerops,            /* OBJT_SG */
  157         &mgtdevicepagerops,     /* OBJT_MGTDEVICE */
  158 };
  159 
  160 static const int npagers = sizeof(pagertab) / sizeof(pagertab[0]);
  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 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[npagers]; 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 }
  211 
  212 /*
  213  * Allocate an instance of a pager of the given type.
  214  * Size, protection and offset parameters are passed in for pagers that
  215  * need to perform page-level validation (e.g. the device pager).
  216  */
  217 vm_object_t
  218 vm_pager_allocate(objtype_t type, void *handle, vm_ooffset_t size,
  219     vm_prot_t prot, vm_ooffset_t off, struct ucred *cred)
  220 {
  221         vm_object_t ret;
  222         struct pagerops *ops;
  223 
  224         ops = pagertab[type];
  225         if (ops)
  226                 ret = (*ops->pgo_alloc)(handle, size, prot, off, cred);
  227         else
  228                 ret = NULL;
  229         return (ret);
  230 }
  231 
  232 /*
  233  *      The object must be locked.
  234  */
  235 void
  236 vm_pager_deallocate(vm_object_t object)
  237 {
  238 
  239         VM_OBJECT_ASSERT_WLOCKED(object);
  240         (*pagertab[object->type]->pgo_dealloc) (object);
  241 }
  242 
  243 /*
  244  * vm_pager_get_pages() - inline, see vm/vm_pager.h
  245  * vm_pager_put_pages() - inline, see vm/vm_pager.h
  246  * vm_pager_has_page() - inline, see vm/vm_pager.h
  247  */
  248 
  249 /*
  250  * Search the specified pager object list for an object with the
  251  * specified handle.  If an object with the specified handle is found,
  252  * increase its reference count and return it.  Otherwise, return NULL.
  253  *
  254  * The pager object list must be locked.
  255  */
  256 vm_object_t
  257 vm_pager_object_lookup(struct pagerlst *pg_list, void *handle)
  258 {
  259         vm_object_t object;
  260 
  261         TAILQ_FOREACH(object, pg_list, pager_object_list) {
  262                 if (object->handle == handle) {
  263                         VM_OBJECT_WLOCK(object);
  264                         if ((object->flags & OBJ_DEAD) == 0) {
  265                                 vm_object_reference_locked(object);
  266                                 VM_OBJECT_WUNLOCK(object);
  267                                 break;
  268                         }
  269                         VM_OBJECT_WUNLOCK(object);
  270                 }
  271         }
  272         return (object);
  273 }
  274 
  275 /*
  276  * initialize a physical buffer
  277  */
  278 
  279 /*
  280  * XXX This probably belongs in vfs_bio.c
  281  */
  282 static void
  283 initpbuf(struct buf *bp)
  284 {
  285 
  286         KASSERT(bp->b_bufobj == NULL, ("initpbuf with bufobj"));
  287         KASSERT(bp->b_vp == NULL, ("initpbuf with vp"));
  288         bp->b_rcred = NOCRED;
  289         bp->b_wcred = NOCRED;
  290         bp->b_qindex = 0;       /* On no queue (QUEUE_NONE) */
  291         bp->b_saveaddr = (caddr_t)(MAXPHYS * (bp - swbuf)) + swapbkva;
  292         bp->b_data = bp->b_saveaddr;
  293         bp->b_kvabase = bp->b_saveaddr;
  294         bp->b_kvasize = MAXPHYS;
  295         bp->b_xflags = 0;
  296         bp->b_flags = 0;
  297         bp->b_ioflags = 0;
  298         bp->b_iodone = NULL;
  299         bp->b_error = 0;
  300         BUF_LOCK(bp, LK_EXCLUSIVE, NULL);
  301 }
  302 
  303 /*
  304  * allocate a physical buffer
  305  *
  306  *      There are a limited number (nswbuf) of physical buffers.  We need
  307  *      to make sure that no single subsystem is able to hog all of them,
  308  *      so each subsystem implements a counter which is typically initialized
  309  *      to 1/2 nswbuf.  getpbuf() decrements this counter in allocation and
  310  *      increments it on release, and blocks if the counter hits zero.  A
  311  *      subsystem may initialize the counter to -1 to disable the feature,
  312  *      but it must still be sure to match up all uses of getpbuf() with 
  313  *      relpbuf() using the same variable.
  314  *
  315  *      NOTE: pfreecnt can be NULL, but this 'feature' will be removed
  316  *      relatively soon when the rest of the subsystems get smart about it. XXX
  317  */
  318 struct buf *
  319 getpbuf(int *pfreecnt)
  320 {
  321         struct buf *bp;
  322 
  323         mtx_lock(&pbuf_mtx);
  324         for (;;) {
  325                 if (pfreecnt != NULL) {
  326                         while (*pfreecnt == 0) {
  327                                 msleep(pfreecnt, &pbuf_mtx, PVM, "wswbuf0", 0);
  328                         }
  329                 }
  330 
  331                 /* get a bp from the swap buffer header pool */
  332                 if ((bp = TAILQ_FIRST(&bswlist)) != NULL)
  333                         break;
  334 
  335                 bswneeded = 1;
  336                 msleep(&bswneeded, &pbuf_mtx, PVM, "wswbuf1", 0);
  337                 /* loop in case someone else grabbed one */
  338         }
  339         TAILQ_REMOVE(&bswlist, bp, b_freelist);
  340         if (pfreecnt)
  341                 --*pfreecnt;
  342         mtx_unlock(&pbuf_mtx);
  343         initpbuf(bp);
  344         return (bp);
  345 }
  346 
  347 /*
  348  * allocate a physical buffer, if one is available.
  349  *
  350  *      Note that there is no NULL hack here - all subsystems using this
  351  *      call understand how to use pfreecnt.
  352  */
  353 struct buf *
  354 trypbuf(int *pfreecnt)
  355 {
  356         struct buf *bp;
  357 
  358         mtx_lock(&pbuf_mtx);
  359         if (*pfreecnt == 0 || (bp = TAILQ_FIRST(&bswlist)) == NULL) {
  360                 mtx_unlock(&pbuf_mtx);
  361                 return NULL;
  362         }
  363         TAILQ_REMOVE(&bswlist, bp, b_freelist);
  364         --*pfreecnt;
  365         mtx_unlock(&pbuf_mtx);
  366         initpbuf(bp);
  367         return (bp);
  368 }
  369 
  370 /*
  371  * release a physical buffer
  372  *
  373  *      NOTE: pfreecnt can be NULL, but this 'feature' will be removed
  374  *      relatively soon when the rest of the subsystems get smart about it. XXX
  375  */
  376 void
  377 relpbuf(struct buf *bp, int *pfreecnt)
  378 {
  379 
  380         if (bp->b_rcred != NOCRED) {
  381                 crfree(bp->b_rcred);
  382                 bp->b_rcred = NOCRED;
  383         }
  384         if (bp->b_wcred != NOCRED) {
  385                 crfree(bp->b_wcred);
  386                 bp->b_wcred = NOCRED;
  387         }
  388 
  389         KASSERT(bp->b_vp == NULL, ("relpbuf with vp"));
  390         KASSERT(bp->b_bufobj == NULL, ("relpbuf with bufobj"));
  391 
  392         BUF_UNLOCK(bp);
  393 
  394         mtx_lock(&pbuf_mtx);
  395         TAILQ_INSERT_HEAD(&bswlist, bp, b_freelist);
  396 
  397         if (bswneeded) {
  398                 bswneeded = 0;
  399                 wakeup(&bswneeded);
  400         }
  401         if (pfreecnt) {
  402                 if (++*pfreecnt == 1)
  403                         wakeup(pfreecnt);
  404         }
  405         mtx_unlock(&pbuf_mtx);
  406 }
  407 
  408 /*
  409  * Associate a p-buffer with a vnode.
  410  *
  411  * Also sets B_PAGING flag to indicate that vnode is not fully associated
  412  * with the buffer.  i.e. the bp has not been linked into the vnode or
  413  * ref-counted.
  414  */
  415 void
  416 pbgetvp(struct vnode *vp, struct buf *bp)
  417 {
  418 
  419         KASSERT(bp->b_vp == NULL, ("pbgetvp: not free"));
  420         KASSERT(bp->b_bufobj == NULL, ("pbgetvp: not free (bufobj)"));
  421 
  422         bp->b_vp = vp;
  423         bp->b_flags |= B_PAGING;
  424         bp->b_bufobj = &vp->v_bufobj;
  425 }
  426 
  427 /*
  428  * Associate a p-buffer with a vnode.
  429  *
  430  * Also sets B_PAGING flag to indicate that vnode is not fully associated
  431  * with the buffer.  i.e. the bp has not been linked into the vnode or
  432  * ref-counted.
  433  */
  434 void
  435 pbgetbo(struct bufobj *bo, struct buf *bp)
  436 {
  437 
  438         KASSERT(bp->b_vp == NULL, ("pbgetbo: not free (vnode)"));
  439         KASSERT(bp->b_bufobj == NULL, ("pbgetbo: not free (bufobj)"));
  440 
  441         bp->b_flags |= B_PAGING;
  442         bp->b_bufobj = bo;
  443 }
  444 
  445 /*
  446  * Disassociate a p-buffer from a vnode.
  447  */
  448 void
  449 pbrelvp(struct buf *bp)
  450 {
  451 
  452         KASSERT(bp->b_vp != NULL, ("pbrelvp: NULL"));
  453         KASSERT(bp->b_bufobj != NULL, ("pbrelvp: NULL bufobj"));
  454         KASSERT((bp->b_xflags & (BX_VNDIRTY | BX_VNCLEAN)) == 0,
  455             ("pbrelvp: pager buf on vnode list."));
  456 
  457         bp->b_vp = NULL;
  458         bp->b_bufobj = NULL;
  459         bp->b_flags &= ~B_PAGING;
  460 }
  461 
  462 /*
  463  * Disassociate a p-buffer from a bufobj.
  464  */
  465 void
  466 pbrelbo(struct buf *bp)
  467 {
  468 
  469         KASSERT(bp->b_vp == NULL, ("pbrelbo: vnode"));
  470         KASSERT(bp->b_bufobj != NULL, ("pbrelbo: NULL bufobj"));
  471         KASSERT((bp->b_xflags & (BX_VNDIRTY | BX_VNCLEAN)) == 0,
  472             ("pbrelbo: pager buf on vnode list."));
  473 
  474         bp->b_bufobj = NULL;
  475         bp->b_flags &= ~B_PAGING;
  476 }

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