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