Postcopy: Add stats on page requests
[qemu.git] / page_cache.c
1 /*
2 * Page cache for QEMU
3 * The cache is base on a hash of the page address
4 *
5 * Copyright 2012 Red Hat, Inc. and/or its affiliates
6 *
7 * Authors:
8 * Orit Wasserman <owasserm@redhat.com>
9 *
10 * This work is licensed under the terms of the GNU GPL, version 2 or later.
11 * See the COPYING file in the top-level directory.
12 *
13 */
14
15 #include "qemu/osdep.h"
16
17 #include "qemu-common.h"
18 #include "qemu/host-utils.h"
19 #include "migration/page_cache.h"
20
21 #ifdef DEBUG_CACHE
22 #define DPRINTF(fmt, ...) \
23 do { fprintf(stdout, "cache: " fmt, ## __VA_ARGS__); } while (0)
24 #else
25 #define DPRINTF(fmt, ...) \
26 do { } while (0)
27 #endif
28
29 /* the page in cache will not be replaced in two cycles */
30 #define CACHED_PAGE_LIFETIME 2
31
32 typedef struct CacheItem CacheItem;
33
34 struct CacheItem {
35 uint64_t it_addr;
36 uint64_t it_age;
37 uint8_t *it_data;
38 };
39
40 struct PageCache {
41 CacheItem *page_cache;
42 unsigned int page_size;
43 int64_t max_num_items;
44 uint64_t max_item_age;
45 int64_t num_items;
46 };
47
48 PageCache *cache_init(int64_t num_pages, unsigned int page_size)
49 {
50 int64_t i;
51
52 PageCache *cache;
53
54 if (num_pages <= 0) {
55 DPRINTF("invalid number of pages\n");
56 return NULL;
57 }
58
59 /* We prefer not to abort if there is no memory */
60 cache = g_try_malloc(sizeof(*cache));
61 if (!cache) {
62 DPRINTF("Failed to allocate cache\n");
63 return NULL;
64 }
65 /* round down to the nearest power of 2 */
66 if (!is_power_of_2(num_pages)) {
67 num_pages = pow2floor(num_pages);
68 DPRINTF("rounding down to %" PRId64 "\n", num_pages);
69 }
70 cache->page_size = page_size;
71 cache->num_items = 0;
72 cache->max_item_age = 0;
73 cache->max_num_items = num_pages;
74
75 DPRINTF("Setting cache buckets to %" PRId64 "\n", cache->max_num_items);
76
77 /* We prefer not to abort if there is no memory */
78 cache->page_cache = g_try_malloc((cache->max_num_items) *
79 sizeof(*cache->page_cache));
80 if (!cache->page_cache) {
81 DPRINTF("Failed to allocate cache->page_cache\n");
82 g_free(cache);
83 return NULL;
84 }
85
86 for (i = 0; i < cache->max_num_items; i++) {
87 cache->page_cache[i].it_data = NULL;
88 cache->page_cache[i].it_age = 0;
89 cache->page_cache[i].it_addr = -1;
90 }
91
92 return cache;
93 }
94
95 void cache_fini(PageCache *cache)
96 {
97 int64_t i;
98
99 g_assert(cache);
100 g_assert(cache->page_cache);
101
102 for (i = 0; i < cache->max_num_items; i++) {
103 g_free(cache->page_cache[i].it_data);
104 }
105
106 g_free(cache->page_cache);
107 cache->page_cache = NULL;
108 g_free(cache);
109 }
110
111 static size_t cache_get_cache_pos(const PageCache *cache,
112 uint64_t address)
113 {
114 size_t pos;
115
116 g_assert(cache->max_num_items);
117 pos = (address / cache->page_size) & (cache->max_num_items - 1);
118 return pos;
119 }
120
121 static CacheItem *cache_get_by_addr(const PageCache *cache, uint64_t addr)
122 {
123 size_t pos;
124
125 g_assert(cache);
126 g_assert(cache->page_cache);
127
128 pos = cache_get_cache_pos(cache, addr);
129
130 return &cache->page_cache[pos];
131 }
132
133 uint8_t *get_cached_data(const PageCache *cache, uint64_t addr)
134 {
135 return cache_get_by_addr(cache, addr)->it_data;
136 }
137
138 bool cache_is_cached(const PageCache *cache, uint64_t addr,
139 uint64_t current_age)
140 {
141 CacheItem *it;
142
143 it = cache_get_by_addr(cache, addr);
144
145 if (it->it_addr == addr) {
146 /* update the it_age when the cache hit */
147 it->it_age = current_age;
148 return true;
149 }
150 return false;
151 }
152
153 int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata,
154 uint64_t current_age)
155 {
156
157 CacheItem *it;
158
159 /* actual update of entry */
160 it = cache_get_by_addr(cache, addr);
161
162 if (it->it_data && it->it_addr != addr &&
163 it->it_age + CACHED_PAGE_LIFETIME > current_age) {
164 /* the cache page is fresh, don't replace it */
165 return -1;
166 }
167 /* allocate page */
168 if (!it->it_data) {
169 it->it_data = g_try_malloc(cache->page_size);
170 if (!it->it_data) {
171 DPRINTF("Error allocating page\n");
172 return -1;
173 }
174 cache->num_items++;
175 }
176
177 memcpy(it->it_data, pdata, cache->page_size);
178
179 it->it_age = current_age;
180 it->it_addr = addr;
181
182 return 0;
183 }
184
185 int64_t cache_resize(PageCache *cache, int64_t new_num_pages)
186 {
187 PageCache *new_cache;
188 int64_t i;
189
190 CacheItem *old_it, *new_it;
191
192 g_assert(cache);
193
194 /* cache was not inited */
195 if (cache->page_cache == NULL) {
196 return -1;
197 }
198
199 /* same size */
200 if (pow2floor(new_num_pages) == cache->max_num_items) {
201 return cache->max_num_items;
202 }
203
204 new_cache = cache_init(new_num_pages, cache->page_size);
205 if (!(new_cache)) {
206 DPRINTF("Error creating new cache\n");
207 return -1;
208 }
209
210 /* move all data from old cache */
211 for (i = 0; i < cache->max_num_items; i++) {
212 old_it = &cache->page_cache[i];
213 if (old_it->it_addr != -1) {
214 /* check for collision, if there is, keep MRU page */
215 new_it = cache_get_by_addr(new_cache, old_it->it_addr);
216 if (new_it->it_data && new_it->it_age >= old_it->it_age) {
217 /* keep the MRU page */
218 g_free(old_it->it_data);
219 } else {
220 if (!new_it->it_data) {
221 new_cache->num_items++;
222 }
223 g_free(new_it->it_data);
224 new_it->it_data = old_it->it_data;
225 new_it->it_age = old_it->it_age;
226 new_it->it_addr = old_it->it_addr;
227 }
228 }
229 }
230
231 g_free(cache->page_cache);
232 cache->page_cache = new_cache->page_cache;
233 cache->max_num_items = new_cache->max_num_items;
234 cache->num_items = new_cache->num_items;
235
236 g_free(new_cache);
237
238 return cache->max_num_items;
239 }