migration/page_cache.c

   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 "qemu-common.h"
  18 #include "qemu/host-utils.h"
  19 #include "migration/page_cache.h"
  20
  21 #ifdef DEBUG_CACHE
  22 #define DPRINTF(fmt, ...) \
  23     do { fprintf(stdout, "cache: " fmt, ## __VA_ARGS__); } while (0)
  24 #else
  25 #define DPRINTF(fmt, ...) \
  26     do { } while (0)
  27 #endif
  28
  29 /* the page in cache will not be replaced in two cycles */
  30 #define CACHED_PAGE_LIFETIME 2
  31
  32 typedef struct CacheItem CacheItem;
  33
  34 struct CacheItem {
  35     uint64_t it_addr;
  36     uint64_t it_age;
  37     uint8_t *it_data;
  38 };
  39
  40 struct PageCache {
  41     CacheItem *page_cache;
  42     unsigned int page_size;
  43     int64_t max_num_items;
  44     int64_t num_items;
  45 };
  46
  47 PageCache *cache_init(int64_t num_pages, unsigned int page_size)
  48 {
  49     int64_t i;
  50
  51     PageCache *cache;
  52
  53     if (num_pages <= 0) {
  54         DPRINTF("invalid number of pages\n");
  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         DPRINTF("Failed to allocate cache\n");
  62         return NULL;
  63     }
  64     /* round down to the nearest power of 2 */
  65     if (!is_power_of_2(num_pages)) {
  66         num_pages = pow2floor(num_pages);
  67         DPRINTF("rounding down to %" PRId64 "\n", num_pages);
  68     }
  69     cache->page_size = page_size;
  70     cache->num_items = 0;
  71     cache->max_num_items = num_pages;
  72
  73     DPRINTF("Setting cache buckets to %" PRId64 "\n", cache->max_num_items);
  74
  75     /* We prefer not to abort if there is no memory */
  76     cache->page_cache = g_try_malloc((cache->max_num_items) *
  77                                      sizeof(*cache->page_cache));
  78     if (!cache->page_cache) {
  79         DPRINTF("Failed to allocate cache->page_cache\n");
  80         g_free(cache);
  81         return NULL;
  82     }
  83
  84     for (i = 0; i < cache->max_num_items; i++) {
  85         cache->page_cache[i].it_data = NULL;
  86         cache->page_cache[i].it_age = 0;
  87         cache->page_cache[i].it_addr = -1;
  88     }
  89
  90     return cache;
  91 }
  92
  93 void cache_fini(PageCache *cache)
  94 {
  95     int64_t i;
  96
  97     g_assert(cache);
  98     g_assert(cache->page_cache);
  99
 100     for (i = 0; i < cache->max_num_items; i++) {
 101         g_free(cache->page_cache[i].it_data);
 102     }
 103
 104     g_free(cache->page_cache);
 105     cache->page_cache = NULL;
 106     g_free(cache);
 107 }
 108
 109 static size_t cache_get_cache_pos(const PageCache *cache,
 110                                   uint64_t address)
 111 {
 112     g_assert(cache->max_num_items);
 113     return (address / cache->page_size) & (cache->max_num_items - 1);
 114 }
 115
 116 static CacheItem *cache_get_by_addr(const PageCache *cache, uint64_t addr)
 117 {
 118     size_t pos;
 119
 120     g_assert(cache);
 121     g_assert(cache->page_cache);
 122
 123     pos = cache_get_cache_pos(cache, addr);
 124
 125     return &cache->page_cache[pos];
 126 }
 127
 128 uint8_t *get_cached_data(const PageCache *cache, uint64_t addr)
 129 {
 130     return cache_get_by_addr(cache, addr)->it_data;
 131 }
 132
 133 bool cache_is_cached(const PageCache *cache, uint64_t addr,
 134                      uint64_t current_age)
 135 {
 136     CacheItem *it;
 137
 138     it = cache_get_by_addr(cache, addr);
 139
 140     if (it->it_addr == addr) {
 141         /* update the it_age when the cache hit */
 142         it->it_age = current_age;
 143         return true;
 144     }
 145     return false;
 146 }
 147
 148 int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata,
 149                  uint64_t current_age)
 150 {
 151
 152     CacheItem *it;
 153
 154     /* actual update of entry */
 155     it = cache_get_by_addr(cache, addr);
 156
 157     if (it->it_data && it->it_addr != addr &&
 158         it->it_age + CACHED_PAGE_LIFETIME > current_age) {
 159         /* the cache page is fresh, don't replace it */
 160         return -1;
 161     }
 162     /* allocate page */
 163     if (!it->it_data) {
 164         it->it_data = g_try_malloc(cache->page_size);
 165         if (!it->it_data) {
 166             DPRINTF("Error allocating page\n");
 167             return -1;
 168         }
 169         cache->num_items++;
 170     }
 171
 172     memcpy(it->it_data, pdata, cache->page_size);
 173
 174     it->it_age = current_age;
 175     it->it_addr = addr;
 176
 177     return 0;
 178 }