qemu

FORK: QEMU emulator
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page_cache.c (4251B)

      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 }