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 <stdint.h>
  16 #include <stdio.h>
  17 #include <stdlib.h>
  18 #include <strings.h>
  19 #include <string.h>
  20 #include <sys/time.h>
  21 #include <sys/types.h>
  22 #include <stdbool.h>
  23 #include <glib.h>
  24
  25 #include "qemu-common.h"
  26 #include "migration/page_cache.h"
  27
  28 #ifdef DEBUG_CACHE
  29 #define DPRINTF(fmt, ...) \
  30     do { fprintf(stdout, "cache: " fmt, ## __VA_ARGS__); } while (0)
  31 #else
  32 #define DPRINTF(fmt, ...) \
  33     do { } while (0)
  34 #endif
  35
  36 typedef struct CacheItem CacheItem;
  37
  38 struct CacheItem {
  39     uint64_t it_addr;
  40     uint64_t it_age;
  41     uint8_t *it_data;
  42 };
  43
  44 struct PageCache {
  45     CacheItem *page_cache;
  46     unsigned int page_size;
  47     int64_t max_num_items;
  48     uint64_t max_item_age;
  49     int64_t num_items;
  50 };
  51
  52 PageCache *cache_init(int64_t num_pages, unsigned int page_size)
  53 {
  54     int64_t i;
  55
  56     PageCache *cache;
  57
  58     if (num_pages <= 0) {
  59         DPRINTF("invalid number of pages\n");
  60         return NULL;
  61     }
  62
  63     cache = g_malloc(sizeof(*cache));
  64
  65     /* round down to the nearest power of 2 */
  66     if (!is_power_of_2(num_pages)) {
  67         num_pages = pow2floor(num_pages);
  68         DPRINTF("rounding down to %" PRId64 "\n", num_pages);
  69     }
  70     cache->page_size = page_size;
  71     cache->num_items = 0;
  72     cache->max_item_age = 0;
  73     cache->max_num_items = num_pages;
  74
  75     DPRINTF("Setting cache buckets to %" PRId64 "\n", cache->max_num_items);
  76
  77     cache->page_cache = g_malloc((cache->max_num_items) *
  78                                  sizeof(*cache->page_cache));
  79
  80     for (i = 0; i < cache->max_num_items; i++) {
  81         cache->page_cache[i].it_data = NULL;
  82         cache->page_cache[i].it_age = 0;
  83         cache->page_cache[i].it_addr = -1;
  84     }
  85
  86     return cache;
  87 }
  88
  89 void cache_fini(PageCache *cache)
  90 {
  91     int64_t i;
  92
  93     g_assert(cache);
  94     g_assert(cache->page_cache);
  95
  96     for (i = 0; i < cache->max_num_items; i++) {
  97         g_free(cache->page_cache[i].it_data);
  98     }
  99
 100     g_free(cache->page_cache);
 101     cache->page_cache = NULL;
 102 }
 103
 104 static size_t cache_get_cache_pos(const PageCache *cache,
 105                                   uint64_t address)
 106 {
 107     size_t pos;
 108
 109     g_assert(cache->max_num_items);
 110     pos = (address / cache->page_size) & (cache->max_num_items - 1);
 111     return pos;
 112 }
 113
 114 bool cache_is_cached(const PageCache *cache, uint64_t addr)
 115 {
 116     size_t pos;
 117
 118     g_assert(cache);
 119     g_assert(cache->page_cache);
 120
 121     pos = cache_get_cache_pos(cache, addr);
 122
 123     return (cache->page_cache[pos].it_addr == addr);
 124 }
 125
 126 static CacheItem *cache_get_by_addr(const PageCache *cache, uint64_t addr)
 127 {
 128     size_t pos;
 129
 130     g_assert(cache);
 131     g_assert(cache->page_cache);
 132
 133     pos = cache_get_cache_pos(cache, addr);
 134
 135     return &cache->page_cache[pos];
 136 }
 137
 138 uint8_t *get_cached_data(const PageCache *cache, uint64_t addr)
 139 {
 140     return cache_get_by_addr(cache, addr)->it_data;
 141 }
 142
 143 void cache_insert(PageCache *cache, uint64_t addr, uint8_t *pdata)
 144 {
 145
 146     CacheItem *it = NULL;
 147
 148     g_assert(cache);
 149     g_assert(cache->page_cache);
 150
 151     /* actual update of entry */
 152     it = cache_get_by_addr(cache, addr);
 153
 154     /* free old cached data if any */
 155     g_free(it->it_data);
 156
 157     if (!it->it_data) {
 158         cache->num_items++;
 159     }
 160
 161     it->it_data = g_memdup(pdata, cache->page_size);
 162     it->it_age = ++cache->max_item_age;
 163     it->it_addr = addr;
 164 }
 165
 166 int64_t cache_resize(PageCache *cache, int64_t new_num_pages)
 167 {
 168     PageCache *new_cache;
 169     int64_t i;
 170
 171     CacheItem *old_it, *new_it;
 172
 173     g_assert(cache);
 174
 175     /* cache was not inited */
 176     if (cache->page_cache == NULL) {
 177         return -1;
 178     }
 179
 180     /* same size */
 181     if (pow2floor(new_num_pages) == cache->max_num_items) {
 182         return cache->max_num_items;
 183     }
 184
 185     new_cache = cache_init(new_num_pages, cache->page_size);
 186     if (!(new_cache)) {
 187         DPRINTF("Error creating new cache\n");
 188         return -1;
 189     }
 190
 191     /* move all data from old cache */
 192     for (i = 0; i < cache->max_num_items; i++) {
 193         old_it = &cache->page_cache[i];
 194         if (old_it->it_addr != -1) {
 195             /* check for collision, if there is, keep MRU page */
 196             new_it = cache_get_by_addr(new_cache, old_it->it_addr);
 197             if (new_it->it_data && new_it->it_age >= old_it->it_age) {
 198                 /* keep the MRU page */
 199                 g_free(old_it->it_data);
 200             } else {
 201                 if (!new_it->it_data) {
 202                     new_cache->num_items++;
 203                 }
 204                 g_free(new_it->it_data);
 205                 new_it->it_data = old_it->it_data;
 206                 new_it->it_age = old_it->it_age;
 207                 new_it->it_addr = old_it->it_addr;
 208             }
 209         }
 210     }
 211
 212     g_free(cache->page_cache);
 213     cache->page_cache = new_cache->page_cache;
 214     cache->max_num_items = new_cache->max_num_items;
 215     cache->num_items = new_cache->num_items;
 216
 217     g_free(new_cache);
 218
 219     return cache->max_num_items;
 220 }