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