Merge remote-tracking branch 'remotes/dgilbert/tags/pull-migration-20200925a' into...
[qemu.git] / migration / 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 "qapi/qmp/qerror.h"
18 #include "qapi/error.h"
19 #include "qemu/host-utils.h"
20 #include "page_cache.h"
21
22 #ifdef DEBUG_CACHE
23 #define DPRINTF(fmt, ...) \
24 do { fprintf(stdout, "cache: " fmt, ## __VA_ARGS__); } while (0)
25 #else
26 #define DPRINTF(fmt, ...) \
27 do { } while (0)
28 #endif
29
30 /* the page in cache will not be replaced in two cycles */
31 #define CACHED_PAGE_LIFETIME 2
32
33 typedef struct CacheItem CacheItem;
34
35 struct CacheItem {
36 uint64_t it_addr;
37 uint64_t it_age;
38 uint8_t *it_data;
39 };
40
41 struct PageCache {
42 CacheItem *page_cache;
43 size_t page_size;
44 size_t max_num_items;
45 size_t num_items;
46 };
47
48 PageCache *cache_init(int64_t new_size, size_t page_size, Error **errp)
49 {
50 int64_t i;
51 size_t num_pages = new_size / page_size;
52 PageCache *cache;
53
54 if (new_size < page_size) {
55 error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "cache size",
56 "is smaller than one target page size");
57 return NULL;
58 }
59
60 /* round down to the nearest power of 2 */
61 if (!is_power_of_2(num_pages)) {
62 error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "cache size",
63 "is not a power of two number of pages");
64 return NULL;
65 }
66
67 /* We prefer not to abort if there is no memory */
68 cache = g_try_malloc(sizeof(*cache));
69 if (!cache) {
70 error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "cache size",
71 "Failed to allocate cache");
72 return NULL;
73 }
74 cache->page_size = page_size;
75 cache->num_items = 0;
76 cache->max_num_items = num_pages;
77
78 DPRINTF("Setting cache buckets to %" PRId64 "\n", cache->max_num_items);
79
80 /* We prefer not to abort if there is no memory */
81 cache->page_cache = g_try_malloc((cache->max_num_items) *
82 sizeof(*cache->page_cache));
83 if (!cache->page_cache) {
84 error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "cache size",
85 "Failed to allocate page cache");
86 g_free(cache);
87 return NULL;
88 }
89
90 for (i = 0; i < cache->max_num_items; i++) {
91 cache->page_cache[i].it_data = NULL;
92 cache->page_cache[i].it_age = 0;
93 cache->page_cache[i].it_addr = -1;
94 }
95
96 return cache;
97 }
98
99 void cache_fini(PageCache *cache)
100 {
101 int64_t i;
102
103 g_assert(cache);
104 g_assert(cache->page_cache);
105
106 for (i = 0; i < cache->max_num_items; i++) {
107 g_free(cache->page_cache[i].it_data);
108 }
109
110 g_free(cache->page_cache);
111 cache->page_cache = NULL;
112 g_free(cache);
113 }
114
115 static size_t cache_get_cache_pos(const PageCache *cache,
116 uint64_t address)
117 {
118 g_assert(cache->max_num_items);
119 return (address / cache->page_size) & (cache->max_num_items - 1);
120 }
121
122 static CacheItem *cache_get_by_addr(const PageCache *cache, uint64_t addr)
123 {
124 size_t pos;
125
126 g_assert(cache);
127 g_assert(cache->page_cache);
128
129 pos = cache_get_cache_pos(cache, addr);
130
131 return &cache->page_cache[pos];
132 }
133
134 uint8_t *get_cached_data(const PageCache *cache, uint64_t addr)
135 {
136 return cache_get_by_addr(cache, addr)->it_data;
137 }
138
139 bool cache_is_cached(const PageCache *cache, uint64_t addr,
140 uint64_t current_age)
141 {
142 CacheItem *it;
143
144 it = cache_get_by_addr(cache, addr);
145
146 if (it->it_addr == addr) {
147 /* update the it_age when the cache hit */
148 it->it_age = current_age;
149 return true;
150 }
151 return false;
152 }
153
154 int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata,
155 uint64_t current_age)
156 {
157
158 CacheItem *it;
159
160 /* actual update of entry */
161 it = cache_get_by_addr(cache, addr);
162
163 if (it->it_data && it->it_addr != addr &&
164 it->it_age + CACHED_PAGE_LIFETIME > current_age) {
165 /* the cache page is fresh, don't replace it */
166 return -1;
167 }
168 /* allocate page */
169 if (!it->it_data) {
170 it->it_data = g_try_malloc(cache->page_size);
171 if (!it->it_data) {
172 DPRINTF("Error allocating page\n");
173 return -1;
174 }
175 cache->num_items++;
176 }
177
178 memcpy(it->it_data, pdata, cache->page_size);
179
180 it->it_age = current_age;
181 it->it_addr = addr;
182
183 return 0;
184 }