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     /* We prefer not to abort if there is no memory */
  64     cache = g_try_malloc(sizeof(*cache));
  65     if (!cache) {
  66         DPRINTF("Failed to allocate cache\n");
  67         return NULL;
  68     }
  69     /* round down to the nearest power of 2 */
  70     if (!is_power_of_2(num_pages)) {
  71         num_pages = pow2floor(num_pages);
  72         DPRINTF("rounding down to %" PRId64 "\n", num_pages);
  73     }
  74     cache->page_size = page_size;
  75     cache->num_items = 0;
  76     cache->max_item_age = 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         DPRINTF("Failed to allocate cache->page_cache\n");
  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     size_t pos;
 119
 120     g_assert(cache->max_num_items);
 121     pos = (address / cache->page_size) & (cache->max_num_items - 1);
 122     return pos;
 123 }
 124
 125 bool cache_is_cached(const PageCache *cache, uint64_t addr)
 126 {
 127     size_t pos;
 128
 129     g_assert(cache);
 130     g_assert(cache->page_cache);
 131
 132     pos = cache_get_cache_pos(cache, addr);
 133
 134     return (cache->page_cache[pos].it_addr == addr);
 135 }
 136
 137 static CacheItem *cache_get_by_addr(const PageCache *cache, uint64_t addr)
 138 {
 139     size_t pos;
 140
 141     g_assert(cache);
 142     g_assert(cache->page_cache);
 143
 144     pos = cache_get_cache_pos(cache, addr);
 145
 146     return &cache->page_cache[pos];
 147 }
 148
 149 uint8_t *get_cached_data(const PageCache *cache, uint64_t addr)
 150 {
 151     return cache_get_by_addr(cache, addr)->it_data;
 152 }
 153
 154 int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata)
 155 {
 156
 157     CacheItem *it = NULL;
 158
 159     g_assert(cache);
 160     g_assert(cache->page_cache);
 161
 162     /* actual update of entry */
 163     it = cache_get_by_addr(cache, addr);
 164
 165     /* allocate page */
 166     if (!it->it_data) {
 167         it->it_data = g_try_malloc(cache->page_size);
 168         if (!it->it_data) {
 169             DPRINTF("Error allocating page\n");
 170             return -1;
 171         }
 172         cache->num_items++;
 173     }
 174
 175     memcpy(it->it_data, pdata, cache->page_size);
 176
 177     it->it_age = ++cache->max_item_age;
 178     it->it_addr = addr;
 179
 180     return 0;
 181 }
 182
 183 int64_t cache_resize(PageCache *cache, int64_t new_num_pages)
 184 {
 185     PageCache *new_cache;
 186     int64_t i;
 187
 188     CacheItem *old_it, *new_it;
 189
 190     g_assert(cache);
 191
 192     /* cache was not inited */
 193     if (cache->page_cache == NULL) {
 194         return -1;
 195     }
 196
 197     /* same size */
 198     if (pow2floor(new_num_pages) == cache->max_num_items) {
 199         return cache->max_num_items;
 200     }
 201
 202     new_cache = cache_init(new_num_pages, cache->page_size);
 203     if (!(new_cache)) {
 204         DPRINTF("Error creating new cache\n");
 205         return -1;
 206     }
 207
 208     /* move all data from old cache */
 209     for (i = 0; i < cache->max_num_items; i++) {
 210         old_it = &cache->page_cache[i];
 211         if (old_it->it_addr != -1) {
 212             /* check for collision, if there is, keep MRU page */
 213             new_it = cache_get_by_addr(new_cache, old_it->it_addr);
 214             if (new_it->it_data && new_it->it_age >= old_it->it_age) {
 215                 /* keep the MRU page */
 216                 g_free(old_it->it_data);
 217             } else {
 218                 if (!new_it->it_data) {
 219                     new_cache->num_items++;
 220                 }
 221                 g_free(new_it->it_data);
 222                 new_it->it_data = old_it->it_data;
 223                 new_it->it_age = old_it->it_age;
 224                 new_it->it_addr = old_it->it_addr;
 225             }
 226         }
 227     }
 228
 229     g_free(cache->page_cache);
 230     cache->page_cache = new_cache->page_cache;
 231     cache->max_num_items = new_cache->max_num_items;
 232     cache->num_items = new_cache->num_items;
 233
 234     g_free(new_cache);
 235
 236     return cache->max_num_items;
 237 }