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