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-common.h" 20 #include "qemu/host-utils.h" 21 #include "page_cache.h" 22 23 #ifdef DEBUG_CACHE 24 #define DPRINTF(fmt, ...) \ 25 do { fprintf(stdout, "cache: " fmt, ## __VA_ARGS__); } while (0) 26 #else 27 #define DPRINTF(fmt, ...) \ 28 do { } while (0) 29 #endif 30 31 /* the page in cache will not be replaced in two cycles */ 32 #define CACHED_PAGE_LIFETIME 2 33 34 typedef struct CacheItem CacheItem; 35 36 struct CacheItem { 37 uint64_t it_addr; 38 uint64_t it_age; 39 uint8_t *it_data; 40 }; 41 42 struct PageCache { 43 CacheItem *page_cache; 44 size_t page_size; 45 size_t max_num_items; 46 size_t num_items; 47 }; 48 49 PageCache *cache_init(int64_t new_size, size_t page_size, Error **errp) 50 { 51 int64_t i; 52 size_t num_pages = new_size / page_size; 53 PageCache *cache; 54 55 if (new_size < page_size) { 56 error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "cache size", 57 "is smaller than one target page size"); 58 return NULL; 59 } 60 61 /* round down to the nearest power of 2 */ 62 if (!is_power_of_2(num_pages)) { 63 error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "cache size", 64 "is not a power of two number of pages"); 65 return NULL; 66 } 67 68 /* We prefer not to abort if there is no memory */ 69 cache = g_try_malloc(sizeof(*cache)); 70 if (!cache) { 71 error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "cache size", 72 "Failed to allocate cache"); 73 return NULL; 74 } 75 cache->page_size = page_size; 76 cache->num_items = 0; 77 cache->max_num_items = num_pages; 78 79 DPRINTF("Setting cache buckets to %" PRId64 "\n", cache->max_num_items); 80 81 /* We prefer not to abort if there is no memory */ 82 cache->page_cache = g_try_malloc((cache->max_num_items) * 83 sizeof(*cache->page_cache)); 84 if (!cache->page_cache) { 85 error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "cache size", 86 "Failed to allocate page cache"); 87 g_free(cache); 88 return NULL; 89 } 90 91 for (i = 0; i < cache->max_num_items; i++) { 92 cache->page_cache[i].it_data = NULL; 93 cache->page_cache[i].it_age = 0; 94 cache->page_cache[i].it_addr = -1; 95 } 96 97 return cache; 98 } 99 100 void cache_fini(PageCache *cache) 101 { 102 int64_t i; 103 104 g_assert(cache); 105 g_assert(cache->page_cache); 106 107 for (i = 0; i < cache->max_num_items; i++) { 108 g_free(cache->page_cache[i].it_data); 109 } 110 111 g_free(cache->page_cache); 112 cache->page_cache = NULL; 113 g_free(cache); 114 } 115 116 static size_t cache_get_cache_pos(const PageCache *cache, 117 uint64_t address) 118 { 119 g_assert(cache->max_num_items); 120 return (address / cache->page_size) & (cache->max_num_items - 1); 121 } 122 123 static CacheItem *cache_get_by_addr(const PageCache *cache, uint64_t addr) 124 { 125 size_t pos; 126 127 g_assert(cache); 128 g_assert(cache->page_cache); 129 130 pos = cache_get_cache_pos(cache, addr); 131 132 return &cache->page_cache[pos]; 133 } 134 135 uint8_t *get_cached_data(const PageCache *cache, uint64_t addr) 136 { 137 return cache_get_by_addr(cache, addr)->it_data; 138 } 139 140 bool cache_is_cached(const PageCache *cache, uint64_t addr, 141 uint64_t current_age) 142 { 143 CacheItem *it; 144 145 it = cache_get_by_addr(cache, addr); 146 147 if (it->it_addr == addr) { 148 /* update the it_age when the cache hit */ 149 it->it_age = current_age; 150 return true; 151 } 152 return false; 153 } 154 155 int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata, 156 uint64_t current_age) 157 { 158 159 CacheItem *it; 160 161 /* actual update of entry */ 162 it = cache_get_by_addr(cache, addr); 163 164 if (it->it_data && it->it_addr != addr && 165 it->it_age + CACHED_PAGE_LIFETIME > current_age) { 166 /* the cache page is fresh, don't replace it */ 167 return -1; 168 } 169 /* allocate page */ 170 if (!it->it_data) { 171 it->it_data = g_try_malloc(cache->page_size); 172 if (!it->it_data) { 173 DPRINTF("Error allocating page\n"); 174 return -1; 175 } 176 cache->num_items++; 177 } 178 179 memcpy(it->it_data, pdata, cache->page_size); 180 181 it->it_age = current_age; 182 it->it_addr = addr; 183 184 return 0; 185 } 186