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 }
 113
 114 static size_t cache_get_cache_pos(const PageCache *cache,
 115                                   uint64_t address)
 116 {
 117     size_t pos;
 118
 119     g_assert(cache->max_num_items);
 120     pos = (address / cache->page_size) & (cache->max_num_items - 1);
 121     return pos;
 122 }
 123
 124 bool cache_is_cached(const PageCache *cache, uint64_t addr)
 125 {
 126     size_t pos;
 127
 128     g_assert(cache);
 129     g_assert(cache->page_cache);
 130
 131     pos = cache_get_cache_pos(cache, addr);
 132
 133     return (cache->page_cache[pos].it_addr == addr);
 134 }
 135
 136 static CacheItem *cache_get_by_addr(const PageCache *cache, uint64_t addr)
 137 {
 138     size_t pos;
 139
 140     g_assert(cache);
 141     g_assert(cache->page_cache);
 142
 143     pos = cache_get_cache_pos(cache, addr);
 144
 145     return &cache->page_cache[pos];
 146 }
 147
 148 uint8_t *get_cached_data(const PageCache *cache, uint64_t addr)
 149 {
 150     return cache_get_by_addr(cache, addr)->it_data;
 151 }
 152
 153 int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata)
 154 {
 155
 156     CacheItem *it = NULL;
 157
 158     g_assert(cache);
 159     g_assert(cache->page_cache);
 160
 161     /* actual update of entry */
 162     it = cache_get_by_addr(cache, addr);
 163
 164     /* allocate page */
 165     if (!it->it_data) {
 166         it->it_data = g_try_malloc(cache->page_size);
 167         if (!it->it_data) {
 168             DPRINTF("Error allocating page\n");
 169             return -1;
 170         }
 171         cache->num_items++;
 172     }
 173
 174     memcpy(it->it_data, pdata, cache->page_size);
 175
 176     it->it_age = ++cache->max_item_age;
 177     it->it_addr = addr;
 178
 179     return 0;
 180 }
 181
 182 int64_t cache_resize(PageCache *cache, int64_t new_num_pages)
 183 {
 184     PageCache *new_cache;
 185     int64_t i;
 186
 187     CacheItem *old_it, *new_it;
 188
 189     g_assert(cache);
 190
 191     /* cache was not inited */
 192     if (cache->page_cache == NULL) {
 193         return -1;
 194     }
 195
 196     /* same size */
 197     if (pow2floor(new_num_pages) == cache->max_num_items) {
 198         return cache->max_num_items;
 199     }
 200
 201     new_cache = cache_init(new_num_pages, cache->page_size);
 202     if (!(new_cache)) {
 203         DPRINTF("Error creating new cache\n");
 204         return -1;
 205     }
 206
 207     /* move all data from old cache */
 208     for (i = 0; i < cache->max_num_items; i++) {
 209         old_it = &cache->page_cache[i];
 210         if (old_it->it_addr != -1) {
 211             /* check for collision, if there is, keep MRU page */
 212             new_it = cache_get_by_addr(new_cache, old_it->it_addr);
 213             if (new_it->it_data && new_it->it_age >= old_it->it_age) {
 214                 /* keep the MRU page */
 215                 g_free(old_it->it_data);
 216             } else {
 217                 if (!new_it->it_data) {
 218                     new_cache->num_items++;
 219                 }
 220                 g_free(new_it->it_data);
 221                 new_it->it_data = old_it->it_data;
 222                 new_it->it_age = old_it->it_age;
 223                 new_it->it_addr = old_it->it_addr;
 224             }
 225         }
 226     }
 227
 228     g_free(cache->page_cache);
 229     cache->page_cache = new_cache->page_cache;
 230     cache->max_num_items = new_cache->max_num_items;
 231     cache->num_items = new_cache->num_items;
 232
 233     g_free(new_cache);
 234
 235     return cache->max_num_items;
 236 }