sys/vm/default_pager.c

   1 /*
   2  * Copyright (c) 1995, David Greenman
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. All advertising materials mentioning features or use of this software
  14  *    must display the following acknowledgement:
  15  *      This product includes software developed by David Greenman.
  16  * 4. The name of the author may not be used to endorse or promote products
  17  *    derived from this software without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  29  * SUCH DAMAGE.
  30  *
  31  * The default pager is responsible for supplying backing store to unbacked
  32  * storage.  The backing store is usually swap so we just fall through to
  33  * the swap routines.  However, since swap metadata has not been assigned,
  34  * the swap routines assign and manage the swap backing store through the
  35  * vm_page->swapblk field.  The object is only converted when the page is
  36  * physically freed after having been cleaned and even then vm_page->swapblk
  37  * is maintained whenever a resident page also has swap backing store.
  38  *
  39  * $FreeBSD: src/sys/vm/default_pager.c,v 1.23 1999/11/07 20:03:53 alc Exp $
  40  * $DragonFly: src/sys/vm/default_pager.c,v 1.5 2006/03/27 01:54:18 dillon Exp $
  41  */
  42
  43 #include <sys/param.h>
  44 #include <sys/systm.h>
  45
  46 #include <vm/vm.h>
  47 #include <vm/vm_object.h>
  48 #include <vm/vm_page.h>
  49 #include <vm/vm_pager.h>
  50 #include <vm/swap_pager.h>
  51
  52 static void default_pager_dealloc (vm_object_t);
  53 static int default_pager_getpage (vm_object_t, vm_page_t *, int);
  54 static void default_pager_putpages (vm_object_t, vm_page_t *, int,
  55                 boolean_t, int *);
  56 static boolean_t default_pager_haspage (vm_object_t, vm_pindex_t);
  57 /*
  58  * pagerops for OBJT_DEFAULT - "default pager".
  59  */
  60 struct pagerops defaultpagerops = {
  61         default_pager_dealloc,
  62         default_pager_getpage,
  63         default_pager_putpages,
  64         default_pager_haspage
  65 };
  66
  67 /*
  68  * no_pager_alloc just returns an initialized object.
  69  */
  70 vm_object_t
  71 default_pager_alloc(void *handle, off_t size, vm_prot_t prot, off_t offset)
  72 {
  73         vm_object_t object;
  74
  75         if (handle != NULL)
  76                 panic("default_pager_alloc: handle specified");
  77
  78         object = vm_object_allocate(OBJT_DEFAULT,
  79                                     OFF_TO_IDX(round_page64(offset + size)));
  80         return (object);
  81 }
  82
  83 /*
  84  * deallocate resources associated with default objects.   The default objects
  85  * have no special resources allocated to them, but the vm_page's being used
  86  * in this object might.  Still, we do not have to do anything - we will free
  87  * the swapblk in the underlying vm_page's when we free the vm_page or
  88  * garbage collect the vm_page cache list.
  89  */
  90
  91 static void
  92 default_pager_dealloc(vm_object_t object)
  93 {
  94         /*
  95          * OBJT_DEFAULT objects have no special resources allocated to them.
  96          */
  97         KKASSERT(object->swblock_count == 0);
  98 }
  99
 100 /*
 101  * Load pages from backing store.  Since OBJT_DEFAULT is converted to
 102  * OBJT_SWAP at the time a swap-backed vm_page_t is freed, we will never
 103  * see a vm_page with assigned swap here.
 104  */
 105
 106 static int
 107 default_pager_getpage(vm_object_t object, vm_page_t *mpp, int seqaccess)
 108 {
 109         return VM_PAGER_FAIL;
 110 }
 111
 112 /*
 113  * Store pages to backing store.  We should assign swap and initiate
 114  * I/O.  We do not actually convert the object to OBJT_SWAP here.  The
 115  * object will be converted when the written-out vm_page_t is moved from the
 116  * cache to the free list.
 117  */
 118
 119 static void
 120 default_pager_putpages(vm_object_t object, vm_page_t *m, int c, boolean_t sync,
 121     int *rtvals)
 122 {
 123         swap_pager_putpages(object, m, c, sync, rtvals);
 124 }
 125
 126 /*
 127  * Tell us whether the backing store for the requested (object,index) is
 128  * synchronized.  i.e. tell us whether we can throw the page away and
 129  * reload it later.  So, for example, if we are in the process of writing
 130  * the page to its backing store, or if no backing store has been assigned,
 131  * it is not yet synchronized.
 132  *
 133  * It is possible to have fully-synchronized swap assigned without the
 134  * object having been converted.  We just call swap_pager_haspage() to
 135  * deal with it since it must already deal with it plus deal with swap
 136  * meta-data structures.
 137  */
 138
 139 static boolean_t
 140 default_pager_haspage(vm_object_t object, vm_pindex_t pindex)
 141 {
 142         return FALSE;
 143 }