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(int64_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, QERR_INVALID_PARAMETER_VALUE, "cache size", 49 "is smaller than one target page size"); 50 return NULL; 51 } 52 53 /* round down to the nearest power of 2 */ 54 if (!is_power_of_2(num_pages)) { 55 error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "cache size", 56 "is not a power of two number of pages"); 57 return NULL; 58 } 59 60 /* We prefer not to abort if there is no memory */ 61 cache = g_try_malloc(sizeof(*cache)); 62 if (!cache) { 63 error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "cache size", 64 "Failed to allocate cache"); 65 return NULL; 66 } 67 cache->page_size = page_size; 68 cache->num_items = 0; 69 cache->max_num_items = num_pages; 70 71 trace_migration_pagecache_init(cache->max_num_items); 72 73 /* We prefer not to abort if there is no memory */ 74 cache->page_cache = g_try_malloc((cache->max_num_items) * 75 sizeof(*cache->page_cache)); 76 if (!cache->page_cache) { 77 error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "cache size", 78 "Failed to allocate page cache"); 79 g_free(cache); 80 return NULL; 81 } 82 83 for (i = 0; i < cache->max_num_items; i++) { 84 cache->page_cache[i].it_data = NULL; 85 cache->page_cache[i].it_age = 0; 86 cache->page_cache[i].it_addr = -1; 87 } 88 89 return cache; 90 } 91 92 void cache_fini(PageCache *cache) 93 { 94 int64_t i; 95 96 g_assert(cache); 97 g_assert(cache->page_cache); 98 99 for (i = 0; i < cache->max_num_items; i++) { 100 g_free(cache->page_cache[i].it_data); 101 } 102 103 g_free(cache->page_cache); 104 cache->page_cache = NULL; 105 g_free(cache); 106 } 107 108 static size_t cache_get_cache_pos(const PageCache *cache, 109 uint64_t address) 110 { 111 g_assert(cache->max_num_items); 112 return (address / cache->page_size) & (cache->max_num_items - 1); 113 } 114 115 static CacheItem *cache_get_by_addr(const PageCache *cache, uint64_t addr) 116 { 117 size_t pos; 118 119 g_assert(cache); 120 g_assert(cache->page_cache); 121 122 pos = cache_get_cache_pos(cache, addr); 123 124 return &cache->page_cache[pos]; 125 } 126 127 uint8_t *get_cached_data(const PageCache *cache, uint64_t addr) 128 { 129 return cache_get_by_addr(cache, addr)->it_data; 130 } 131 132 bool cache_is_cached(const PageCache *cache, uint64_t addr, 133 uint64_t current_age) 134 { 135 CacheItem *it; 136 137 it = cache_get_by_addr(cache, addr); 138 139 if (it->it_addr == addr) { 140 /* update the it_age when the cache hit */ 141 it->it_age = current_age; 142 return true; 143 } 144 return false; 145 } 146 147 int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata, 148 uint64_t current_age) 149 { 150 151 CacheItem *it; 152 153 /* actual update of entry */ 154 it = cache_get_by_addr(cache, addr); 155 156 if (it->it_data && it->it_addr != addr && 157 it->it_age + CACHED_PAGE_LIFETIME > current_age) { 158 /* the cache page is fresh, don't replace it */ 159 return -1; 160 } 161 /* allocate page */ 162 if (!it->it_data) { 163 it->it_data = g_try_malloc(cache->page_size); 164 if (!it->it_data) { 165 trace_migration_pagecache_insert(); 166 return -1; 167 } 168 cache->num_items++; 169 } 170 171 memcpy(it->it_data, pdata, cache->page_size); 172 173 it->it_age = current_age; 174 it->it_addr = addr; 175 176 return 0; 177 } 178