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