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: releng/8.2/sys/vm/default_pager.c 199583 2009-11-20 15:27:52Z jhb $");
   42 
   43 #include <sys/param.h>
   44 #include <sys/systm.h>
   45 #include <sys/lock.h>
   46 #include <sys/proc.h>
   47 #include <sys/resourcevar.h>
   48 #include <sys/mutex.h>
   49 
   50 #include <vm/vm.h>
   51 #include <vm/vm_object.h>
   52 #include <vm/vm_page.h>
   53 #include <vm/vm_pager.h>
   54 #include <vm/swap_pager.h>
   55 
   56 static vm_object_t default_pager_alloc(void *, vm_ooffset_t, vm_prot_t,
   57     vm_ooffset_t, struct ucred *);
   58 static void default_pager_dealloc(vm_object_t);
   59 static int default_pager_getpages(vm_object_t, vm_page_t *, int, int);
   60 static void default_pager_putpages(vm_object_t, vm_page_t *, int, 
   61                 boolean_t, int *);
   62 static boolean_t default_pager_haspage(vm_object_t, vm_pindex_t, int *, 
   63                 int *);
   64 /*
   65  * pagerops for OBJT_DEFAULT - "default pager".
   66  */
   67 struct pagerops defaultpagerops = {
   68         .pgo_alloc =    default_pager_alloc,
   69         .pgo_dealloc =  default_pager_dealloc,
   70         .pgo_getpages = default_pager_getpages,
   71         .pgo_putpages = default_pager_putpages,
   72         .pgo_haspage =  default_pager_haspage,
   73 };
   74 
   75 /*
   76  * no_pager_alloc just returns an initialized object.
   77  */
   78 static vm_object_t
   79 default_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
   80     vm_ooffset_t offset, struct ucred *cred)
   81 {
   82         vm_object_t object;
   83         struct uidinfo *uip;
   84 
   85         if (handle != NULL)
   86                 panic("default_pager_alloc: handle specified");
   87         if (cred != NULL) {
   88                 uip = cred->cr_ruidinfo;
   89                 if (!swap_reserve_by_uid(size, uip))
   90                         return (NULL);
   91                 uihold(uip);
   92         }
   93         object = vm_object_allocate(OBJT_DEFAULT,
   94             OFF_TO_IDX(round_page(offset + size)));
   95         if (cred != NULL) {
   96                 VM_OBJECT_LOCK(object);
   97                 object->uip = uip;
   98                 object->charge = size;
   99                 VM_OBJECT_UNLOCK(object);
  100         }
  101         return (object);
  102 }
  103 
  104 /*
  105  * deallocate resources associated with default objects.   The default objects
  106  * have no special resources allocated to them, but the vm_page's being used
  107  * in this object might.  Still, we do not have to do anything - we will free
  108  * the swapblk in the underlying vm_page's when we free the vm_page or
  109  * garbage collect the vm_page cache list.
  110  */
  111 static void
  112 default_pager_dealloc(object)
  113         vm_object_t object;
  114 {
  115         /*
  116          * OBJT_DEFAULT objects have no special resources allocated to them.
  117          */
  118 }
  119 
  120 /*
  121  * Load pages from backing store.  Since OBJT_DEFAULT is converted to
  122  * OBJT_SWAP at the time a swap-backed vm_page_t is freed, we will never
  123  * see a vm_page with assigned swap here.
  124  */
  125 static int
  126 default_pager_getpages(object, m, count, reqpage)
  127         vm_object_t object;
  128         vm_page_t *m;
  129         int count;
  130         int reqpage;
  131 {
  132         return VM_PAGER_FAIL;
  133 }
  134 
  135 /*
  136  * Store pages to backing store.  We should assign swap and initiate
  137  * I/O.  We do not actually convert the object to OBJT_SWAP here.  The
  138  * object will be converted when the written-out vm_page_t is moved from the
  139  * cache to the free list.
  140  */
  141 static void
  142 default_pager_putpages(object, m, c, sync, rtvals)
  143         vm_object_t object;
  144         vm_page_t *m;
  145         int c;
  146         boolean_t sync;
  147         int *rtvals;
  148 {
  149         swappagerops.pgo_putpages(object, m, c, sync, rtvals);
  150 }
  151 
  152 /*
  153  * Tell us whether the backing store for the requested (object,index) is
  154  * synchronized.  i.e. tell us whether we can throw the page away and 
  155  * reload it later.  So, for example, if we are in the process of writing
  156  * the page to its backing store, or if no backing store has been assigned,
  157  * it is not yet synchronized.
  158  *
  159  * It is possible to have fully-synchronized swap assigned without the
  160  * object having been converted.  We just call swap_pager_haspage() to
  161  * deal with it since it must already deal with it plus deal with swap
  162  * meta-data structures.
  163  */
  164 static boolean_t
  165 default_pager_haspage(object, pindex, before, after)
  166         vm_object_t object;
  167         vm_pindex_t pindex;
  168         int *before;
  169         int *after;
  170 {
  171         return FALSE;
  172 }
  173 

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