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/*
* Page cache for QEMU
* The cache is base on a hash of the page address
*
* Copyright 2012 Red Hat, Inc. and/or its affiliates
*
* Authors:
* Orit Wasserman <owasserm@redhat.com>
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*
*/
#include "qemu/osdep.h"
#include "qemu-common.h"
#include "qemu/host-utils.h"
#include "migration/page_cache.h"
#ifdef DEBUG_CACHE
#define DPRINTF(fmt, ...) \
do { fprintf(stdout, "cache: " fmt, ## __VA_ARGS__); } while (0)
#else
#define DPRINTF(fmt, ...) \
do { } while (0)
#endif
/* the page in cache will not be replaced in two cycles */
#define CACHED_PAGE_LIFETIME 2
typedef struct CacheItem CacheItem;
struct CacheItem {
uint64_t it_addr;
uint64_t it_age;
uint8_t *it_data;
};
struct PageCache {
CacheItem *page_cache;
unsigned int page_size;
int64_t max_num_items;
uint64_t max_item_age;
int64_t num_items;
};
PageCache *cache_init(int64_t num_pages, unsigned int page_size)
{
int64_t i;
PageCache *cache;
if (num_pages <= 0) {
DPRINTF("invalid number of pages\n");
return NULL;
}
/* We prefer not to abort if there is no memory */
cache = g_try_malloc(sizeof(*cache));
if (!cache) {
DPRINTF("Failed to allocate cache\n");
return NULL;
}
/* round down to the nearest power of 2 */
if (!is_power_of_2(num_pages)) {
num_pages = pow2floor(num_pages);
DPRINTF("rounding down to %" PRId64 "\n", num_pages);
}
cache->page_size = page_size;
cache->num_items = 0;
cache->max_item_age = 0;
cache->max_num_items = num_pages;
DPRINTF("Setting cache buckets to %" PRId64 "\n", cache->max_num_items);
/* We prefer not to abort if there is no memory */
cache->page_cache = g_try_malloc((cache->max_num_items) *
sizeof(*cache->page_cache));
if (!cache->page_cache) {
DPRINTF("Failed to allocate cache->page_cache\n");
g_free(cache);
return NULL;
}
for (i = 0; i < cache->max_num_items; i++) {
cache->page_cache[i].it_data = NULL;
cache->page_cache[i].it_age = 0;
cache->page_cache[i].it_addr = -1;
}
return cache;
}
void cache_fini(PageCache *cache)
{
int64_t i;
g_assert(cache);
g_assert(cache->page_cache);
for (i = 0; i < cache->max_num_items; i++) {
g_free(cache->page_cache[i].it_data);
}
g_free(cache->page_cache);
cache->page_cache = NULL;
g_free(cache);
}
static size_t cache_get_cache_pos(const PageCache *cache,
uint64_t address)
{
g_assert(cache->max_num_items);
return (address / cache->page_size) & (cache->max_num_items - 1);
}
static CacheItem *cache_get_by_addr(const PageCache *cache, uint64_t addr)
{
size_t pos;
g_assert(cache);
g_assert(cache->page_cache);
pos = cache_get_cache_pos(cache, addr);
return &cache->page_cache[pos];
}
uint8_t *get_cached_data(const PageCache *cache, uint64_t addr)
{
return cache_get_by_addr(cache, addr)->it_data;
}
bool cache_is_cached(const PageCache *cache, uint64_t addr,
uint64_t current_age)
{
CacheItem *it;
it = cache_get_by_addr(cache, addr);
if (it->it_addr == addr) {
/* update the it_age when the cache hit */
it->it_age = current_age;
return true;
}
return false;
}
int cache_insert(PageCache *cache, uint64_t addr, const uint8_t *pdata,
uint64_t current_age)
{
CacheItem *it;
/* actual update of entry */
it = cache_get_by_addr(cache, addr);
if (it->it_data && it->it_addr != addr &&
it->it_age + CACHED_PAGE_LIFETIME > current_age) {
/* the cache page is fresh, don't replace it */
return -1;
}
/* allocate page */
if (!it->it_data) {
it->it_data = g_try_malloc(cache->page_size);
if (!it->it_data) {
DPRINTF("Error allocating page\n");
return -1;
}
cache->num_items++;
}
memcpy(it->it_data, pdata, cache->page_size);
it->it_age = current_age;
it->it_addr = addr;
return 0;
}
int64_t cache_resize(PageCache *cache, int64_t new_num_pages)
{
PageCache *new_cache;
int64_t i;
CacheItem *old_it, *new_it;
g_assert(cache);
/* cache was not inited */
if (cache->page_cache == NULL) {
return -1;
}
/* same size */
if (pow2floor(new_num_pages) == cache->max_num_items) {
return cache->max_num_items;
}
new_cache = cache_init(new_num_pages, cache->page_size);
if (!(new_cache)) {
DPRINTF("Error creating new cache\n");
return -1;
}
/* move all data from old cache */
for (i = 0; i < cache->max_num_items; i++) {
old_it = &cache->page_cache[i];
if (old_it->it_addr != -1) {
/* check for collision, if there is, keep MRU page */
new_it = cache_get_by_addr(new_cache, old_it->it_addr);
if (new_it->it_data && new_it->it_age >= old_it->it_age) {
/* keep the MRU page */
g_free(old_it->it_data);
} else {
if (!new_it->it_data) {
new_cache->num_items++;
}
g_free(new_it->it_data);
new_it->it_data = old_it->it_data;
new_it->it_age = old_it->it_age;
new_it->it_addr = old_it->it_addr;
}
}
}
g_free(cache->page_cache);
cache->page_cache = new_cache->page_cache;
cache->max_num_items = new_cache->max_num_items;
cache->num_items = new_cache->num_items;
g_free(new_cache);
return cache->max_num_items;
}
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