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/10.0/sys/vm/vm_pager.c 252330 2013-06-28 03:51:20Z jeff $");
   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         return NULL;
  111 }
  112 
  113 static void
  114 dead_pager_putpages(object, m, count, flags, rtvals)
  115         vm_object_t object;
  116         vm_page_t *m;
  117         int count;
  118         int flags;
  119         int *rtvals;
  120 {
  121         int i;
  122 
  123         for (i = 0; i < count; i++) {
  124                 rtvals[i] = VM_PAGER_AGAIN;
  125         }
  126 }
  127 
  128 static int
  129 dead_pager_haspage(object, pindex, prev, next)
  130         vm_object_t object;
  131         vm_pindex_t pindex;
  132         int *prev;
  133         int *next;
  134 {
  135         if (prev)
  136                 *prev = 0;
  137         if (next)
  138                 *next = 0;
  139         return FALSE;
  140 }
  141 
  142 static void
  143 dead_pager_dealloc(object)
  144         vm_object_t object;
  145 {
  146         return;
  147 }
  148 
  149 static struct pagerops deadpagerops = {
  150         .pgo_alloc =    dead_pager_alloc,
  151         .pgo_dealloc =  dead_pager_dealloc,
  152         .pgo_getpages = dead_pager_getpages,
  153         .pgo_putpages = dead_pager_putpages,
  154         .pgo_haspage =  dead_pager_haspage,
  155 };
  156 
  157 struct pagerops *pagertab[] = {
  158         &defaultpagerops,       /* OBJT_DEFAULT */
  159         &swappagerops,          /* OBJT_SWAP */
  160         &vnodepagerops,         /* OBJT_VNODE */
  161         &devicepagerops,        /* OBJT_DEVICE */
  162         &physpagerops,          /* OBJT_PHYS */
  163         &deadpagerops,          /* OBJT_DEAD */
  164         &sgpagerops,            /* OBJT_SG */
  165         &mgtdevicepagerops,     /* OBJT_MGTDEVICE */
  166 };
  167 
  168 static const int npagers = sizeof(pagertab) / sizeof(pagertab[0]);
  169 
  170 /*
  171  * Kernel address space for mapping pages.
  172  * Used by pagers where KVAs are needed for IO.
  173  *
  174  * XXX needs to be large enough to support the number of pending async
  175  * cleaning requests (NPENDINGIO == 64) * the maximum swap cluster size
  176  * (MAXPHYS == 64k) if you want to get the most efficiency.
  177  */
  178 struct mtx_padalign pbuf_mtx;
  179 static TAILQ_HEAD(swqueue, buf) bswlist;
  180 static int bswneeded;
  181 vm_offset_t swapbkva;           /* swap buffers kva */
  182 
  183 void
  184 vm_pager_init()
  185 {
  186         struct pagerops **pgops;
  187 
  188         TAILQ_INIT(&bswlist);
  189         /*
  190          * Initialize known pagers
  191          */
  192         for (pgops = pagertab; pgops < &pagertab[npagers]; pgops++)
  193                 if ((*pgops)->pgo_init != NULL)
  194                         (*(*pgops)->pgo_init) ();
  195 }
  196 
  197 void
  198 vm_pager_bufferinit()
  199 {
  200         struct buf *bp;
  201         int i;
  202 
  203         mtx_init(&pbuf_mtx, "pbuf mutex", NULL, MTX_DEF);
  204         bp = swbuf;
  205         /*
  206          * Now set up swap and physical I/O buffer headers.
  207          */
  208         for (i = 0; i < nswbuf; i++, bp++) {
  209                 TAILQ_INSERT_HEAD(&bswlist, bp, b_freelist);
  210                 BUF_LOCKINIT(bp);
  211                 LIST_INIT(&bp->b_dep);
  212                 bp->b_rcred = bp->b_wcred = NOCRED;
  213                 bp->b_xflags = 0;
  214         }
  215 
  216         cluster_pbuf_freecnt = nswbuf / 2;
  217         vnode_pbuf_freecnt = nswbuf / 2 + 1;
  218 }
  219 
  220 /*
  221  * Allocate an instance of a pager of the given type.
  222  * Size, protection and offset parameters are passed in for pagers that
  223  * need to perform page-level validation (e.g. the device pager).
  224  */
  225 vm_object_t
  226 vm_pager_allocate(objtype_t type, void *handle, vm_ooffset_t size,
  227     vm_prot_t prot, vm_ooffset_t off, struct ucred *cred)
  228 {
  229         vm_object_t ret;
  230         struct pagerops *ops;
  231 
  232         ops = pagertab[type];
  233         if (ops)
  234                 ret = (*ops->pgo_alloc) (handle, size, prot, off, cred);
  235         else
  236                 ret = NULL;
  237         return (ret);
  238 }
  239 
  240 /*
  241  *      The object must be locked.
  242  */
  243 void
  244 vm_pager_deallocate(object)
  245         vm_object_t object;
  246 {
  247 
  248         VM_OBJECT_ASSERT_WLOCKED(object);
  249         (*pagertab[object->type]->pgo_dealloc) (object);
  250 }
  251 
  252 /*
  253  * vm_pager_get_pages() - inline, see vm/vm_pager.h
  254  * vm_pager_put_pages() - inline, see vm/vm_pager.h
  255  * vm_pager_has_page() - inline, see vm/vm_pager.h
  256  */
  257 
  258 /*
  259  * Search the specified pager object list for an object with the
  260  * specified handle.  If an object with the specified handle is found,
  261  * increase its reference count and return it.  Otherwise, return NULL.
  262  *
  263  * The pager object list must be locked.
  264  */
  265 vm_object_t
  266 vm_pager_object_lookup(struct pagerlst *pg_list, void *handle)
  267 {
  268         vm_object_t object;
  269 
  270         TAILQ_FOREACH(object, pg_list, pager_object_list) {
  271                 if (object->handle == handle) {
  272                         VM_OBJECT_WLOCK(object);
  273                         if ((object->flags & OBJ_DEAD) == 0) {
  274                                 vm_object_reference_locked(object);
  275                                 VM_OBJECT_WUNLOCK(object);
  276                                 break;
  277                         }
  278                         VM_OBJECT_WUNLOCK(object);
  279                 }
  280         }
  281         return (object);
  282 }
  283 
  284 /*
  285  * initialize a physical buffer
  286  */
  287 
  288 /*
  289  * XXX This probably belongs in vfs_bio.c
  290  */
  291 static void
  292 initpbuf(struct buf *bp)
  293 {
  294         KASSERT(bp->b_bufobj == NULL, ("initpbuf with bufobj"));
  295         KASSERT(bp->b_vp == NULL, ("initpbuf with vp"));
  296         bp->b_rcred = NOCRED;
  297         bp->b_wcred = NOCRED;
  298         bp->b_qindex = 0;       /* On no queue (QUEUE_NONE) */
  299         bp->b_saveaddr = (caddr_t) (MAXPHYS * (bp - swbuf)) + swapbkva;
  300         bp->b_data = bp->b_saveaddr;
  301         bp->b_kvabase = bp->b_saveaddr;
  302         bp->b_kvasize = MAXPHYS;
  303         bp->b_xflags = 0;
  304         bp->b_flags = 0;
  305         bp->b_ioflags = 0;
  306         bp->b_iodone = NULL;
  307         bp->b_error = 0;
  308         BUF_LOCK(bp, LK_EXCLUSIVE, NULL);
  309 }
  310 
  311 /*
  312  * allocate a physical buffer
  313  *
  314  *      There are a limited number (nswbuf) of physical buffers.  We need
  315  *      to make sure that no single subsystem is able to hog all of them,
  316  *      so each subsystem implements a counter which is typically initialized
  317  *      to 1/2 nswbuf.  getpbuf() decrements this counter in allocation and
  318  *      increments it on release, and blocks if the counter hits zero.  A
  319  *      subsystem may initialize the counter to -1 to disable the feature,
  320  *      but it must still be sure to match up all uses of getpbuf() with 
  321  *      relpbuf() using the same variable.
  322  *
  323  *      NOTE: pfreecnt can be NULL, but this 'feature' will be removed
  324  *      relatively soon when the rest of the subsystems get smart about it. XXX
  325  */
  326 struct buf *
  327 getpbuf(int *pfreecnt)
  328 {
  329         struct buf *bp;
  330 
  331         mtx_lock(&pbuf_mtx);
  332 
  333         for (;;) {
  334                 if (pfreecnt) {
  335                         while (*pfreecnt == 0) {
  336                                 msleep(pfreecnt, &pbuf_mtx, PVM, "wswbuf0", 0);
  337                         }
  338                 }
  339 
  340                 /* get a bp from the swap buffer header pool */
  341                 if ((bp = TAILQ_FIRST(&bswlist)) != NULL)
  342                         break;
  343 
  344                 bswneeded = 1;
  345                 msleep(&bswneeded, &pbuf_mtx, PVM, "wswbuf1", 0);
  346                 /* loop in case someone else grabbed one */
  347         }
  348         TAILQ_REMOVE(&bswlist, bp, b_freelist);
  349         if (pfreecnt)
  350                 --*pfreecnt;
  351         mtx_unlock(&pbuf_mtx);
  352 
  353         initpbuf(bp);
  354         return bp;
  355 }
  356 
  357 /*
  358  * allocate a physical buffer, if one is available.
  359  *
  360  *      Note that there is no NULL hack here - all subsystems using this
  361  *      call understand how to use pfreecnt.
  362  */
  363 struct buf *
  364 trypbuf(int *pfreecnt)
  365 {
  366         struct buf *bp;
  367 
  368         mtx_lock(&pbuf_mtx);
  369         if (*pfreecnt == 0 || (bp = TAILQ_FIRST(&bswlist)) == NULL) {
  370                 mtx_unlock(&pbuf_mtx);
  371                 return NULL;
  372         }
  373         TAILQ_REMOVE(&bswlist, bp, b_freelist);
  374 
  375         --*pfreecnt;
  376 
  377         mtx_unlock(&pbuf_mtx);
  378 
  379         initpbuf(bp);
  380 
  381         return bp;
  382 }
  383 
  384 /*
  385  * release a physical buffer
  386  *
  387  *      NOTE: pfreecnt can be NULL, but this 'feature' will be removed
  388  *      relatively soon when the rest of the subsystems get smart about it. XXX
  389  */
  390 void
  391 relpbuf(struct buf *bp, int *pfreecnt)
  392 {
  393 
  394         if (bp->b_rcred != NOCRED) {
  395                 crfree(bp->b_rcred);
  396                 bp->b_rcred = NOCRED;
  397         }
  398         if (bp->b_wcred != NOCRED) {
  399                 crfree(bp->b_wcred);
  400                 bp->b_wcred = NOCRED;
  401         }
  402 
  403         KASSERT(bp->b_vp == NULL, ("relpbuf with vp"));
  404         KASSERT(bp->b_bufobj == NULL, ("relpbuf with bufobj"));
  405 
  406         BUF_UNLOCK(bp);
  407 
  408         mtx_lock(&pbuf_mtx);
  409         TAILQ_INSERT_HEAD(&bswlist, bp, b_freelist);
  410 
  411         if (bswneeded) {
  412                 bswneeded = 0;
  413                 wakeup(&bswneeded);
  414         }
  415         if (pfreecnt) {
  416                 if (++*pfreecnt == 1)
  417                         wakeup(pfreecnt);
  418         }
  419         mtx_unlock(&pbuf_mtx);
  420 }
  421 
  422 /*
  423  * Associate a p-buffer with a vnode.
  424  *
  425  * Also sets B_PAGING flag to indicate that vnode is not fully associated
  426  * with the buffer.  i.e. the bp has not been linked into the vnode or
  427  * ref-counted.
  428  */
  429 void
  430 pbgetvp(struct vnode *vp, struct buf *bp)
  431 {
  432 
  433         KASSERT(bp->b_vp == NULL, ("pbgetvp: not free"));
  434         KASSERT(bp->b_bufobj == NULL, ("pbgetvp: not free (bufobj)"));
  435 
  436         bp->b_vp = vp;
  437         bp->b_flags |= B_PAGING;
  438         bp->b_bufobj = &vp->v_bufobj;
  439 }
  440 
  441 /*
  442  * Associate a p-buffer with a vnode.
  443  *
  444  * Also sets B_PAGING flag to indicate that vnode is not fully associated
  445  * with the buffer.  i.e. the bp has not been linked into the vnode or
  446  * ref-counted.
  447  */
  448 void
  449 pbgetbo(struct bufobj *bo, struct buf *bp)
  450 {
  451 
  452         KASSERT(bp->b_vp == NULL, ("pbgetbo: not free (vnode)"));
  453         KASSERT(bp->b_bufobj == NULL, ("pbgetbo: not free (bufobj)"));
  454 
  455         bp->b_flags |= B_PAGING;
  456         bp->b_bufobj = bo;
  457 }
  458 
  459 /*
  460  * Disassociate a p-buffer from a vnode.
  461  */
  462 void
  463 pbrelvp(struct buf *bp)
  464 {
  465 
  466         KASSERT(bp->b_vp != NULL, ("pbrelvp: NULL"));
  467         KASSERT(bp->b_bufobj != NULL, ("pbrelvp: NULL bufobj"));
  468         KASSERT((bp->b_xflags & (BX_VNDIRTY | BX_VNCLEAN)) == 0,
  469             ("pbrelvp: pager buf on vnode list."));
  470 
  471         bp->b_vp = NULL;
  472         bp->b_bufobj = NULL;
  473         bp->b_flags &= ~B_PAGING;
  474 }
  475 
  476 /*
  477  * Disassociate a p-buffer from a bufobj.
  478  */
  479 void
  480 pbrelbo(struct buf *bp)
  481 {
  482 
  483         KASSERT(bp->b_vp == NULL, ("pbrelbo: vnode"));
  484         KASSERT(bp->b_bufobj != NULL, ("pbrelbo: NULL bufobj"));
  485         KASSERT((bp->b_xflags & (BX_VNDIRTY | BX_VNCLEAN)) == 0,
  486             ("pbrelbo: pager buf on vnode list."));
  487 
  488         bp->b_bufobj = NULL;
  489         bp->b_flags &= ~B_PAGING;
  490 }

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