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/default_pager.c

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    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 
   40 #include <sys/cdefs.h>
   41 __FBSDID("$FreeBSD: src/sys/vm/default_pager.c,v 1.35 2005/01/07 02:29:26 imp Exp $");
   42 
   43 #include <sys/param.h>
   44 #include <sys/systm.h>
   45 #include <sys/lock.h>
   46 #include <sys/proc.h>
   47 #include <sys/mutex.h>
   48 
   49 #include <vm/vm.h>
   50 #include <vm/vm_object.h>
   51 #include <vm/vm_page.h>
   52 #include <vm/vm_pager.h>
   53 #include <vm/swap_pager.h>
   54 
   55 static vm_object_t default_pager_alloc(void *, vm_ooffset_t, vm_prot_t,
   56                 vm_ooffset_t);
   57 static void default_pager_dealloc(vm_object_t);
   58 static int default_pager_getpages(vm_object_t, vm_page_t *, int, int);
   59 static void default_pager_putpages(vm_object_t, vm_page_t *, int, 
   60                 boolean_t, int *);
   61 static boolean_t default_pager_haspage(vm_object_t, vm_pindex_t, int *, 
   62                 int *);
   63 /*
   64  * pagerops for OBJT_DEFAULT - "default pager".
   65  */
   66 struct pagerops defaultpagerops = {
   67         .pgo_alloc =    default_pager_alloc,
   68         .pgo_dealloc =  default_pager_dealloc,
   69         .pgo_getpages = default_pager_getpages,
   70         .pgo_putpages = default_pager_putpages,
   71         .pgo_haspage =  default_pager_haspage,
   72 };
   73 
   74 /*
   75  * no_pager_alloc just returns an initialized object.
   76  */
   77 static vm_object_t
   78 default_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
   79                     vm_ooffset_t offset)
   80 {
   81         if (handle != NULL)
   82                 panic("default_pager_alloc: handle specified");
   83 
   84         return vm_object_allocate(OBJT_DEFAULT, OFF_TO_IDX(round_page(offset + size)));
   85 }
   86 
   87 /*
   88  * deallocate resources associated with default objects.   The default objects
   89  * have no special resources allocated to them, but the vm_page's being used
   90  * in this object might.  Still, we do not have to do anything - we will free
   91  * the swapblk in the underlying vm_page's when we free the vm_page or
   92  * garbage collect the vm_page cache list.
   93  */
   94 static void
   95 default_pager_dealloc(object)
   96         vm_object_t object;
   97 {
   98         /*
   99          * OBJT_DEFAULT objects have no special resources allocated to them.
  100          */
  101 }
  102 
  103 /*
  104  * Load pages from backing store.  Since OBJT_DEFAULT is converted to
  105  * OBJT_SWAP at the time a swap-backed vm_page_t is freed, we will never
  106  * see a vm_page with assigned swap here.
  107  */
  108 static int
  109 default_pager_getpages(object, m, count, reqpage)
  110         vm_object_t object;
  111         vm_page_t *m;
  112         int count;
  113         int reqpage;
  114 {
  115         return VM_PAGER_FAIL;
  116 }
  117 
  118 /*
  119  * Store pages to backing store.  We should assign swap and initiate
  120  * I/O.  We do not actually convert the object to OBJT_SWAP here.  The
  121  * object will be converted when the written-out vm_page_t is moved from the
  122  * cache to the free list.
  123  */
  124 static void
  125 default_pager_putpages(object, m, c, sync, rtvals)
  126         vm_object_t object;
  127         vm_page_t *m;
  128         int c;
  129         boolean_t sync;
  130         int *rtvals;
  131 {
  132         swappagerops.pgo_putpages(object, m, c, sync, rtvals);
  133 }
  134 
  135 /*
  136  * Tell us whether the backing store for the requested (object,index) is
  137  * synchronized.  i.e. tell us whether we can throw the page away and 
  138  * reload it later.  So, for example, if we are in the process of writing
  139  * the page to its backing store, or if no backing store has been assigned,
  140  * it is not yet synchronized.
  141  *
  142  * It is possible to have fully-synchronized swap assigned without the
  143  * object having been converted.  We just call swap_pager_haspage() to
  144  * deal with it since it must already deal with it plus deal with swap
  145  * meta-data structures.
  146  */
  147 static boolean_t
  148 default_pager_haspage(object, pindex, before, after)
  149         vm_object_t object;
  150         vm_pindex_t pindex;
  151         int *before;
  152         int *after;
  153 {
  154         return FALSE;
  155 }
  156 

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