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 "qapi/qmp/qerror.h"
  18 #include "qapi/error.h"
  19 #include "qemu-common.h"
  20 #include "qemu/host-utils.h"
  21 #include "migration/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 }