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: stable/10/sys/vm/default_pager.c 310363 2016-12-21 11:32:08Z kib $");
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/rwlock.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 * This pager handles anonymous (no handle) swap-backed memory, just
68 * like the swap pager. It allows several optimizations based on the
69 * fact that no pages of a default object can be swapped out. The
70 * most important optimization is in vm_fault(), where the pager is
71 * never asked for a non-resident page. Instead, a freshly allocated
72 * zeroed page is used.
73 *
74 * On the first request to page out a page from a default object, the
75 * object is converted to swap pager type.
76 */
77 struct pagerops defaultpagerops = {
78 .pgo_alloc = default_pager_alloc,
79 .pgo_dealloc = default_pager_dealloc,
80 .pgo_getpages = default_pager_getpages,
81 .pgo_putpages = default_pager_putpages,
82 .pgo_haspage = default_pager_haspage,
83 };
84
85 /*
86 * no_pager_alloc just returns an initialized object.
87 */
88 static vm_object_t
default_pager_alloc(void * handle,vm_ooffset_t size,vm_prot_t prot,vm_ooffset_t offset,struct ucred * cred)89 default_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
90 vm_ooffset_t offset, struct ucred *cred)
91 {
92 vm_object_t object;
93
94 if (handle != NULL)
95 panic("default_pager_alloc: handle specified");
96 if (cred != NULL) {
97 if (!swap_reserve_by_cred(size, cred))
98 return (NULL);
99 crhold(cred);
100 }
101 object = vm_object_allocate(OBJT_DEFAULT,
102 OFF_TO_IDX(round_page(offset + size)));
103 if (cred != NULL) {
104 VM_OBJECT_WLOCK(object);
105 object->cred = cred;
106 object->charge = size;
107 VM_OBJECT_WUNLOCK(object);
108 }
109 return (object);
110 }
111
112 /*
113 * deallocate resources associated with default objects. The default objects
114 * have no special resources allocated to them, but the vm_page's being used
115 * in this object might. Still, we do not have to do anything - we will free
116 * the swapblk in the underlying vm_page's when we free the vm_page or
117 * garbage collect the vm_page cache list.
118 */
119 static void
default_pager_dealloc(object)120 default_pager_dealloc(object)
121 vm_object_t object;
122 {
123 /*
124 * OBJT_DEFAULT objects have no special resources allocated to them.
125 */
126 object->type = OBJT_DEAD;
127 }
128
129 /*
130 * Load pages from backing store. Since OBJT_DEFAULT is converted to
131 * OBJT_SWAP at the time a swap-backed vm_page_t is freed, we will never
132 * see a vm_page with assigned swap here.
133 */
134 static int
default_pager_getpages(object,m,count,reqpage)135 default_pager_getpages(object, m, count, reqpage)
136 vm_object_t object;
137 vm_page_t *m;
138 int count;
139 int reqpage;
140 {
141 return VM_PAGER_FAIL;
142 }
143
144 /*
145 * Store pages to backing store. We should assign swap and initiate
146 * I/O. We do not actually convert the object to OBJT_SWAP here. The
147 * object will be converted when the written-out vm_page_t is moved from the
148 * cache to the free list.
149 */
150 static void
default_pager_putpages(vm_object_t object,vm_page_t * m,int count,int flags,int * rtvals)151 default_pager_putpages(vm_object_t object, vm_page_t *m, int count,
152 int flags, int *rtvals)
153 {
154
155 swappagerops.pgo_putpages(object, m, count, flags, rtvals);
156 }
157
158 /*
159 * Tell us whether the backing store for the requested (object,index) is
160 * synchronized. i.e. tell us whether we can throw the page away and
161 * reload it later. So, for example, if we are in the process of writing
162 * the page to its backing store, or if no backing store has been assigned,
163 * it is not yet synchronized.
164 *
165 * It is possible to have fully-synchronized swap assigned without the
166 * object having been converted. We just call swap_pager_haspage() to
167 * deal with it since it must already deal with it plus deal with swap
168 * meta-data structures.
169 */
170 static boolean_t
default_pager_haspage(object,pindex,before,after)171 default_pager_haspage(object, pindex, before, after)
172 vm_object_t object;
173 vm_pindex_t pindex;
174 int *before;
175 int *after;
176 {
177 return FALSE;
178 }
179
180