Add cache handling functions

Add MRU page cache mechanism.
The page are accessed by their address.

Signed-off-by: Benoit Hudzia <benoit.hudzia@sap.com>
Signed-off-by: Petter Svard <petters@cs.umu.se>
Signed-off-by: Aidan Shribman <aidan.shribman@sap.com>
Signed-off-by: Orit Wasserman <owasserm@redhat.com>

Reviewed-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

1 files changed, 218 insertions, 0 deletions

diff --git a/page_cache.c b/page_cache.c
new file mode 100644
index 0000000000..0294f7e9f6
--- /dev/null
+++ b/page_cache.c
@@ -0,0 +1,218 @@
+/*
+ * 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 <strings.h>
+
+#include "qemu-common.h"
+#include "qemu/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);
+
+    if (!it->it_data) {
+        cache->num_items++;
+    }
+
+    it->it_data = pdata;
+    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) {
+                /* keep the MRU page */
+                if (new_it->it_age >= old_it->it_age) {
+                    g_free(old_it->it_data);
+                } else {
+                    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;
+                }
+            } else {
+                cache_insert(new_cache, old_it->it_addr, old_it->it_data);
+            }
+        }
+    }
+
+    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;
+}