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 } 185