Archipelago » qemu

/*

 * 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 <stdint.h>

#include <stdio.h>

#include <stdlib.h>

#include <strings.h>

#include <string.h>

#include <sys/time.h>

#include <sys/types.h>

#include <stdbool.h>

#include <glib.h>

#include "qemu-common.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

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;

    }

    cache = g_malloc(sizeof(*cache));

    /* 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);

    cache->page_cache = g_malloc((cache->max_num_items) *

                                 sizeof(*cache->page_cache));

    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;

}

static size_t cache_get_cache_pos(const PageCache *cache,

                                  uint64_t address)

{

    size_t pos;

    g_assert(cache->max_num_items);

    pos = (address / cache->page_size) & (cache->max_num_items - 1);

    return pos;

}

bool cache_is_cached(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].it_addr == addr);

}

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;

}

void cache_insert(PageCache *cache, uint64_t addr, uint8_t *pdata)

{

    CacheItem *it = NULL;

    g_assert(cache);

    g_assert(cache->page_cache);

    /* actual update of entry */

    it = cache_get_by_addr(cache, addr);

    /* free old cached data if any */

    g_free(it->it_data);

    if (!it->it_data) {

        cache->num_items++;

    }

    it->it_data = g_memdup(pdata, cache->page_size);

    it->it_age = ++cache->max_item_age;

    it->it_addr = addr;

}

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;

}