/* * 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 <glib.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) { size_t pos; g_assert(cache->max_num_items); pos = (address / cache->page_size) & (cache->max_num_items - 1); return pos; } 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; }