sys/vm/default_pager.c

   1 /*
   2  * (MPSAFE)
   3  *
   4  * Copyright (c) 1995, David Greenman
   5  * All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  * 3. All advertising materials mentioning features or use of this software
  16  *    must display the following acknowledgement:
  17  *      This product includes software developed by David Greenman.
  18  * 4. The name of the author may not be used to endorse or promote products
  19  *    derived from this software without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  *
  33  * The default pager is responsible for supplying backing store to unbacked
  34  * storage.  The backing store is usually swap so we just fall through to
  35  * the swap routines.  However, since swap metadata has not been assigned,
  36  * the swap routines assign and manage the swap backing store through the
  37  * vm_page->swapblk field.  The object is only converted when the page is
  38  * physically freed after having been cleaned and even then vm_page->swapblk
  39  * is maintained whenever a resident page also has swap backing store.
  40  *
  41  * $FreeBSD: src/sys/vm/default_pager.c,v 1.23 1999/11/07 20:03:53 alc Exp $
  42  */
  43
  44 #include <sys/param.h>
  45 #include <sys/systm.h>
  46
  47 #include <vm/vm.h>
  48 #include <vm/vm_object.h>
  49 #include <vm/vm_page.h>
  50 #include <vm/vm_pager.h>
  51 #include <vm/swap_pager.h>
  52
  53 static void default_pager_dealloc (vm_object_t);
  54 static int default_pager_getpage (vm_object_t, vm_page_t *, int);
  55 static void default_pager_putpages (vm_object_t, vm_page_t *, int,
  56                 int, int *);
  57 static boolean_t default_pager_haspage (vm_object_t, vm_pindex_t);
  58 /*
  59  * pagerops for OBJT_DEFAULT - "default pager".
  60  */
  61 struct pagerops defaultpagerops = {
  62         default_pager_dealloc,
  63         default_pager_getpage,
  64         default_pager_putpages,
  65         default_pager_haspage
  66 };
  67
  68 /*
  69  * no_pager_alloc just returns an initialized object.
  70  */
  71 vm_object_t
  72 default_pager_alloc(void *handle, off_t size, vm_prot_t prot, off_t offset)
  73 {
  74         vm_object_t object;
  75
  76         if (handle != NULL)
  77                 panic("default_pager_alloc: handle specified");
  78
  79         object = vm_object_allocate(OBJT_DEFAULT,
  80                                     OFF_TO_IDX(round_page64(offset + size)));
  81         return (object);
  82 }
  83
  84 /*
  85  * deallocate resources associated with default objects.   The default objects
  86  * have no special resources allocated to them, but the vm_page's being used
  87  * in this object might.  Still, we do not have to do anything - we will free
  88  * the swapblk in the underlying vm_page's when we free the vm_page or
  89  * garbage collect the vm_page cache list.
  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 static int
 106 default_pager_getpage(vm_object_t object, vm_page_t *mpp, int seqaccess)
 107 {
 108         return VM_PAGER_FAIL;
 109 }
 110
 111 /*
 112  * Store pages to backing store.  We should assign swap and initiate
 113  * I/O.  We do not actually convert the object to OBJT_SWAP here.  The
 114  * object will be converted when the written-out vm_page_t is moved from the
 115  * cache to the free list.
 116  */
 117 static void
 118 default_pager_putpages(vm_object_t object, vm_page_t *mpp, int count,
 119                        int sync, int *rtvals)
 120 {
 121         swap_pager_putpages(object, mpp, count, sync, rtvals);
 122 }
 123
 124 /*
 125  * Tell us whether the backing store for the requested (object,index) is
 126  * synchronized.  i.e. tell us whether we can throw the page away and
 127  * reload it later.  So, for example, if we are in the process of writing
 128  * the page to its backing store, or if no backing store has been assigned,
 129  * it is not yet synchronized.
 130  *
 131  * It is possible to have fully-synchronized swap assigned without the
 132  * object having been converted.  We just call swap_pager_haspage() to
 133  * deal with it since it must already deal with it plus deal with swap
 134  * meta-data structures.
 135  */
 136 static boolean_t
 137 default_pager_haspage(vm_object_t object, vm_pindex_t pindex)
 138 {
 139         return FALSE;
 140 }