1 /******************************************************************************
2 *
3 * Xen domain paging default policy.
4 *
5 * Copyright (c) 2009 Citrix Systems, Inc. (Patrick Colp)
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation; either version 2 of the License, or
10 * (at your option) any later version.
11 *
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with this program; If not, see <http://www.gnu.org/licenses/>.
19 */
20
21
22 #include "xc_bitops.h"
23 #include "policy.h"
24
25
26 #define DEFAULT_MRU_SIZE (1024 * 16)
27
28
29 static unsigned long *mru;
30 static unsigned int i_mru;
31 static unsigned int mru_size;
32 static unsigned long *bitmap;
33 static unsigned long *unconsumed;
34 static unsigned int unconsumed_cleared;
35 static unsigned long current_gfn;
36 static unsigned long max_pages;
37
38
policy_init(struct xenpaging * paging)39 int policy_init(struct xenpaging *paging)
40 {
41 int i;
42 int rc = -ENOMEM;
43
44 max_pages = paging->max_pages;
45
46 /* Allocate bitmap for pages not to page out */
47 bitmap = bitmap_alloc(max_pages);
48 if ( !bitmap )
49 goto out;
50 /* Allocate bitmap to track unusable pages */
51 unconsumed = bitmap_alloc(max_pages);
52 if ( !unconsumed )
53 goto out;
54
55 /* Initialise MRU list of paged in pages */
56 if ( paging->policy_mru_size > 0 )
57 mru_size = paging->policy_mru_size;
58 else
59 mru_size = paging->policy_mru_size = DEFAULT_MRU_SIZE;
60
61 mru = malloc(sizeof(*mru) * mru_size);
62 if ( mru == NULL )
63 goto out;
64
65 for ( i = 0; i < mru_size; i++ )
66 mru[i] = INVALID_MFN;
67
68 /* Don't page out page 0 */
69 set_bit(0, bitmap);
70
71 /* Start in the middle to avoid paging during BIOS startup */
72 current_gfn = max_pages / 2;
73
74 rc = 0;
75 out:
76 return rc;
77 }
78
policy_choose_victim(struct xenpaging * paging)79 unsigned long policy_choose_victim(struct xenpaging *paging)
80 {
81 xc_interface *xch = paging->xc_handle;
82 unsigned long i;
83
84 /* One iteration over all possible gfns */
85 for ( i = 0; i < max_pages; i++ )
86 {
87 /* Try next gfn */
88 current_gfn++;
89
90 /* Restart on wrap */
91 if ( current_gfn >= max_pages )
92 current_gfn = 0;
93
94 if ( (current_gfn & (BITS_PER_LONG - 1)) == 0 )
95 {
96 /* All gfns busy */
97 if ( ~bitmap[current_gfn >> ORDER_LONG] == 0 || ~unconsumed[current_gfn >> ORDER_LONG] == 0 )
98 {
99 current_gfn += BITS_PER_LONG;
100 i += BITS_PER_LONG;
101 continue;
102 }
103 }
104
105 /* gfn busy */
106 if ( test_bit(current_gfn, bitmap) )
107 continue;
108
109 /* gfn already tested */
110 if ( test_bit(current_gfn, unconsumed) )
111 continue;
112
113 /* gfn found */
114 break;
115 }
116
117 /* Could not nominate any gfn */
118 if ( i >= max_pages )
119 {
120 /* No more pages, wait in poll */
121 paging->use_poll_timeout = 1;
122 /* Count wrap arounds */
123 unconsumed_cleared++;
124 /* Force retry every few seconds (depends on poll() timeout) */
125 if ( unconsumed_cleared > 123)
126 {
127 /* Force retry of unconsumed gfns on next call */
128 bitmap_clear(unconsumed, max_pages);
129 unconsumed_cleared = 0;
130 DPRINTF("clearing unconsumed, current_gfn %lx", current_gfn);
131 }
132 return INVALID_MFN;
133 }
134
135 set_bit(current_gfn, unconsumed);
136 return current_gfn;
137 }
138
policy_notify_paged_out(unsigned long gfn)139 void policy_notify_paged_out(unsigned long gfn)
140 {
141 set_bit(gfn, bitmap);
142 clear_bit(gfn, unconsumed);
143 }
144
policy_handle_paged_in(unsigned long gfn,int do_mru)145 static void policy_handle_paged_in(unsigned long gfn, int do_mru)
146 {
147 unsigned long old_gfn = mru[i_mru & (mru_size - 1)];
148
149 if ( old_gfn != INVALID_MFN )
150 clear_bit(old_gfn, bitmap);
151
152 if (do_mru) {
153 mru[i_mru & (mru_size - 1)] = gfn;
154 } else {
155 clear_bit(gfn, bitmap);
156 mru[i_mru & (mru_size - 1)] = INVALID_MFN;
157 }
158
159 i_mru++;
160 }
161
policy_notify_paged_in(unsigned long gfn)162 void policy_notify_paged_in(unsigned long gfn)
163 {
164 policy_handle_paged_in(gfn, 1);
165 }
166
policy_notify_paged_in_nomru(unsigned long gfn)167 void policy_notify_paged_in_nomru(unsigned long gfn)
168 {
169 policy_handle_paged_in(gfn, 0);
170 }
171
policy_notify_dropped(unsigned long gfn)172 void policy_notify_dropped(unsigned long gfn)
173 {
174 clear_bit(gfn, bitmap);
175 }
176
177
178 /*
179 * Local variables:
180 * mode: C
181 * c-file-style: "BSD"
182 * c-basic-offset: 4
183 * tab-width: 4
184 * indent-tabs-mode: nil
185 * End:
186 */
187