1 files changed, 482 insertions, 0 deletions
diff --git a/fs/mbcache.c b/fs/mbcache.c
new file mode 100644
index 000000000..95b047256
--- /dev/null
+++ b/fs/mbcache.c
@@ -0,0 +1,482 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/spinlock.h>
+#include <linux/slab.h>
+#include <linux/list.h>
+#include <linux/list_bl.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/workqueue.h>
+#include <linux/mbcache.h>
+
+/*
+ * Mbcache is a simple key-value store. Keys need not be unique, however
+ * key-value pairs are expected to be unique (we use this fact in
+ * mb_cache_entry_delete_or_get()).
+ *
+ * Ext2 and ext4 use this cache for deduplication of extended attribute blocks.
+ * Ext4 also uses it for deduplication of xattr values stored in inodes.
+ * They use hash of data as a key and provide a value that may represent a
+ * block or inode number. That's why keys need not be unique (hash of different
+ * data may be the same). However user provided value always uniquely
+ * identifies a cache entry.
+ *
+ * We provide functions for creation and removal of entries, search by key,
+ * and a special "delete entry with given key-value pair" operation. Fixed
+ * size hash table is used for fast key lookups.
+ */
+
+struct mb_cache {
+	/* Hash table of entries */
+	struct hlist_bl_head	*c_hash;
+	/* log2 of hash table size */
+	int			c_bucket_bits;
+	/* Maximum entries in cache to avoid degrading hash too much */
+	unsigned long		c_max_entries;
+	/* Protects c_list, c_entry_count */
+	spinlock_t		c_list_lock;
+	struct list_head	c_list;
+	/* Number of entries in cache */
+	unsigned long		c_entry_count;
+	struct shrinker		c_shrink;
+	/* Work for shrinking when the cache has too many entries */
+	struct work_struct	c_shrink_work;
+};
+
+static struct kmem_cache *mb_entry_cache;
+
+static unsigned long mb_cache_shrink(struct mb_cache *cache,
+				     unsigned long nr_to_scan);
+
+static inline struct hlist_bl_head *mb_cache_entry_head(struct mb_cache *cache,
+							u32 key)
+{
+	return &cache->c_hash[hash_32(key, cache->c_bucket_bits)];
+}
+
+/*
+ * Number of entries to reclaim synchronously when there are too many entries
+ * in cache
+ */
+#define SYNC_SHRINK_BATCH 64
+
+/*
+ * mb_cache_entry_create - create entry in cache
+ * @cache - cache where the entry should be created
+ * @mask - gfp mask with which the entry should be allocated
+ * @key - key of the entry
+ * @value - value of the entry
+ * @reusable - is the entry reusable by others?
+ *
+ * Creates entry in @cache with key @key and value @value. The function returns
+ * -EBUSY if entry with the same key and value already exists in cache.
+ * Otherwise 0 is returned.
+ */
+int mb_cache_entry_create(struct mb_cache *cache, gfp_t mask, u32 key,
+			  u64 value, bool reusable)
+{
+	struct mb_cache_entry *entry, *dup;
+	struct hlist_bl_node *dup_node;
+	struct hlist_bl_head *head;
+
+	/* Schedule background reclaim if there are too many entries */
+	if (cache->c_entry_count >= cache->c_max_entries)
+		schedule_work(&cache->c_shrink_work);
+	/* Do some sync reclaim if background reclaim cannot keep up */
+	if (cache->c_entry_count >= 2*cache->c_max_entries)
+		mb_cache_shrink(cache, SYNC_SHRINK_BATCH);
+
+	entry = kmem_cache_alloc(mb_entry_cache, mask);
+	if (!entry)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&entry->e_list);
+	/*
+	 * We create entry with two references. One reference is kept by the
+	 * hash table, the other reference is used to protect us from
+	 * mb_cache_entry_delete_or_get() until the entry is fully setup. This
+	 * avoids nesting of cache->c_list_lock into hash table bit locks which
+	 * is problematic for RT.
+	 */
+	atomic_set(&entry->e_refcnt, 2);
+	entry->e_key = key;
+	entry->e_value = value;
+	entry->e_flags = 0;
+	if (reusable)
+		set_bit(MBE_REUSABLE_B, &entry->e_flags);
+	head = mb_cache_entry_head(cache, key);
+	hlist_bl_lock(head);
+	hlist_bl_for_each_entry(dup, dup_node, head, e_hash_list) {
+		if (dup->e_key == key && dup->e_value == value) {
+			hlist_bl_unlock(head);
+			kmem_cache_free(mb_entry_cache, entry);
+			return -EBUSY;
+		}
+	}
+	hlist_bl_add_head(&entry->e_hash_list, head);
+	hlist_bl_unlock(head);
+	spin_lock(&cache->c_list_lock);
+	list_add_tail(&entry->e_list, &cache->c_list);
+	cache->c_entry_count++;
+	spin_unlock(&cache->c_list_lock);
+	mb_cache_entry_put(cache, entry);
+
+	return 0;
+}
+EXPORT_SYMBOL(mb_cache_entry_create);
+
+void __mb_cache_entry_free(struct mb_cache *cache, struct mb_cache_entry *entry)
+{
+	struct hlist_bl_head *head;
+
+	head = mb_cache_entry_head(cache, entry->e_key);
+	hlist_bl_lock(head);
+	hlist_bl_del(&entry->e_hash_list);
+	hlist_bl_unlock(head);
+	kmem_cache_free(mb_entry_cache, entry);
+}
+EXPORT_SYMBOL(__mb_cache_entry_free);
+
+/*
+ * mb_cache_entry_wait_unused - wait to be the last user of the entry
+ *
+ * @entry - entry to work on
+ *
+ * Wait to be the last user of the entry.
+ */
+void mb_cache_entry_wait_unused(struct mb_cache_entry *entry)
+{
+	wait_var_event(&entry->e_refcnt, atomic_read(&entry->e_refcnt) <= 2);
+}
+EXPORT_SYMBOL(mb_cache_entry_wait_unused);
+
+static struct mb_cache_entry *__entry_find(struct mb_cache *cache,
+					   struct mb_cache_entry *entry,
+					   u32 key)
+{
+	struct mb_cache_entry *old_entry = entry;
+	struct hlist_bl_node *node;
+	struct hlist_bl_head *head;
+
+	head = mb_cache_entry_head(cache, key);
+	hlist_bl_lock(head);
+	if (entry && !hlist_bl_unhashed(&entry->e_hash_list))
+		node = entry->e_hash_list.next;
+	else
+		node = hlist_bl_first(head);
+	while (node) {
+		entry = hlist_bl_entry(node, struct mb_cache_entry,
+				       e_hash_list);
+		if (entry->e_key == key &&
+		    test_bit(MBE_REUSABLE_B, &entry->e_flags) &&
+		    atomic_inc_not_zero(&entry->e_refcnt))
+			goto out;
+		node = node->next;
+	}
+	entry = NULL;
+out:
+	hlist_bl_unlock(head);
+	if (old_entry)
+		mb_cache_entry_put(cache, old_entry);
+
+	return entry;
+}
+
+/*
+ * mb_cache_entry_find_first - find the first reusable entry with the given key
+ * @cache: cache where we should search
+ * @key: key to look for
+ *
+ * Search in @cache for a reusable entry with key @key. Grabs reference to the
+ * first reusable entry found and returns the entry.
+ */
+struct mb_cache_entry *mb_cache_entry_find_first(struct mb_cache *cache,
+						 u32 key)
+{
+	return __entry_find(cache, NULL, key);
+}
+EXPORT_SYMBOL(mb_cache_entry_find_first);
+
+/*
+ * mb_cache_entry_find_next - find next reusable entry with the same key
+ * @cache: cache where we should search
+ * @entry: entry to start search from
+ *
+ * Finds next reusable entry in the hash chain which has the same key as @entry.
+ * If @entry is unhashed (which can happen when deletion of entry races with the
+ * search), finds the first reusable entry in the hash chain. The function drops
+ * reference to @entry and returns with a reference to the found entry.
+ */
+struct mb_cache_entry *mb_cache_entry_find_next(struct mb_cache *cache,
+						struct mb_cache_entry *entry)
+{
+	return __entry_find(cache, entry, entry->e_key);
+}
+EXPORT_SYMBOL(mb_cache_entry_find_next);
+
+/*
+ * mb_cache_entry_get - get a cache entry by value (and key)
+ * @cache - cache we work with
+ * @key - key
+ * @value - value
+ */
+struct mb_cache_entry *mb_cache_entry_get(struct mb_cache *cache, u32 key,
+					  u64 value)
+{
+	struct hlist_bl_node *node;
+	struct hlist_bl_head *head;
+	struct mb_cache_entry *entry;
+
+	head = mb_cache_entry_head(cache, key);
+	hlist_bl_lock(head);
+	hlist_bl_for_each_entry(entry, node, head, e_hash_list) {
+		if (entry->e_key == key && entry->e_value == value &&
+		    atomic_inc_not_zero(&entry->e_refcnt))
+			goto out;
+	}
+	entry = NULL;
+out:
+	hlist_bl_unlock(head);
+	return entry;
+}
+EXPORT_SYMBOL(mb_cache_entry_get);
+
+/* mb_cache_entry_delete - try to remove a cache entry
+ * @cache - cache we work with
+ * @key - key
+ * @value - value
+ *
+ * Remove entry from cache @cache with key @key and value @value.
+ */
+void mb_cache_entry_delete(struct mb_cache *cache, u32 key, u64 value)
+{
+	struct hlist_bl_node *node;
+	struct hlist_bl_head *head;
+	struct mb_cache_entry *entry;
+
+	head = mb_cache_entry_head(cache, key);
+	hlist_bl_lock(head);
+	hlist_bl_for_each_entry(entry, node, head, e_hash_list) {
+		if (entry->e_key == key && entry->e_value == value) {
+			/* We keep hash list reference to keep entry alive */
+			hlist_bl_del_init(&entry->e_hash_list);
+			hlist_bl_unlock(head);
+			spin_lock(&cache->c_list_lock);
+			if (!list_empty(&entry->e_list)) {
+				list_del_init(&entry->e_list);
+				if (!WARN_ONCE(cache->c_entry_count == 0,
+		"mbcache: attempt to decrement c_entry_count past zero"))
+					cache->c_entry_count--;
+				atomic_dec(&entry->e_refcnt);
+			}
+			spin_unlock(&cache->c_list_lock);
+			mb_cache_entry_put(cache, entry);
+			return;
+		}
+	}
+	hlist_bl_unlock(head);
+}
+EXPORT_SYMBOL(mb_cache_entry_delete);
+
+/* mb_cache_entry_delete_or_get - remove a cache entry if it has no users
+ * @cache - cache we work with
+ * @key - key
+ * @value - value
+ *
+ * Remove entry from cache @cache with key @key and value @value. The removal
+ * happens only if the entry is unused. The function returns NULL in case the
+ * entry was successfully removed or there's no entry in cache. Otherwise the
+ * function grabs reference of the entry that we failed to delete because it
+ * still has users and return it.
+ */
+struct mb_cache_entry *mb_cache_entry_delete_or_get(struct mb_cache *cache,
+						    u32 key, u64 value)
+{
+	struct mb_cache_entry *entry;
+
+	entry = mb_cache_entry_get(cache, key, value);
+	if (!entry)
+		return NULL;
+
+	/*
+	 * Drop the ref we got from mb_cache_entry_get() and the initial hash
+	 * ref if we are the last user
+	 */
+	if (atomic_cmpxchg(&entry->e_refcnt, 2, 0) != 2)
+		return entry;
+
+	spin_lock(&cache->c_list_lock);
+	if (!list_empty(&entry->e_list))
+		list_del_init(&entry->e_list);
+	cache->c_entry_count--;
+	spin_unlock(&cache->c_list_lock);
+	__mb_cache_entry_free(cache, entry);
+	return NULL;
+}
+EXPORT_SYMBOL(mb_cache_entry_delete_or_get);
+
+/* mb_cache_entry_touch - cache entry got used
+ * @cache - cache the entry belongs to
+ * @entry - entry that got used
+ *
+ * Marks entry as used to give hit higher chances of surviving in cache.
+ */
+void mb_cache_entry_touch(struct mb_cache *cache,
+			  struct mb_cache_entry *entry)
+{
+	set_bit(MBE_REFERENCED_B, &entry->e_flags);
+}
+EXPORT_SYMBOL(mb_cache_entry_touch);
+
+static unsigned long mb_cache_count(struct shrinker *shrink,
+				    struct shrink_control *sc)
+{
+	struct mb_cache *cache = container_of(shrink, struct mb_cache,
+					      c_shrink);
+
+	return cache->c_entry_count;
+}
+
+/* Shrink number of entries in cache */
+static unsigned long mb_cache_shrink(struct mb_cache *cache,
+				     unsigned long nr_to_scan)
+{
+	struct mb_cache_entry *entry;
+	unsigned long shrunk = 0;
+
+	spin_lock(&cache->c_list_lock);
+	while (nr_to_scan-- && !list_empty(&cache->c_list)) {
+		entry = list_first_entry(&cache->c_list,
+					 struct mb_cache_entry, e_list);
+		/* Drop initial hash reference if there is no user */
+		if (test_bit(MBE_REFERENCED_B, &entry->e_flags) ||
+		    atomic_cmpxchg(&entry->e_refcnt, 1, 0) != 1) {
+			clear_bit(MBE_REFERENCED_B, &entry->e_flags);
+			list_move_tail(&entry->e_list, &cache->c_list);
+			continue;
+		}
+		list_del_init(&entry->e_list);
+		cache->c_entry_count--;
+		spin_unlock(&cache->c_list_lock);
+		__mb_cache_entry_free(cache, entry);
+		shrunk++;
+		cond_resched();
+		spin_lock(&cache->c_list_lock);
+	}
+	spin_unlock(&cache->c_list_lock);
+
+	return shrunk;
+}
+
+static unsigned long mb_cache_scan(struct shrinker *shrink,
+				   struct shrink_control *sc)
+{
+	struct mb_cache *cache = container_of(shrink, struct mb_cache,
+					      c_shrink);
+	return mb_cache_shrink(cache, sc->nr_to_scan);
+}
+
+/* We shrink 1/X of the cache when we have too many entries in it */
+#define SHRINK_DIVISOR 16
+
+static void mb_cache_shrink_worker(struct work_struct *work)
+{
+	struct mb_cache *cache = container_of(work, struct mb_cache,
+					      c_shrink_work);
+	mb_cache_shrink(cache, cache->c_max_entries / SHRINK_DIVISOR);
+}
+
+/*
+ * mb_cache_create - create cache
+ * @bucket_bits: log2 of the hash table size
+ *
+ * Create cache for keys with 2^bucket_bits hash entries.
+ */
+struct mb_cache *mb_cache_create(int bucket_bits)
+{
+	struct mb_cache *cache;
+	unsigned long bucket_count = 1UL << bucket_bits;
+	unsigned long i;
+
+	cache = kzalloc(sizeof(struct mb_cache), GFP_KERNEL);
+	if (!cache)
+		goto err_out;
+	cache->c_bucket_bits = bucket_bits;
+	cache->c_max_entries = bucket_count << 4;
+	INIT_LIST_HEAD(&cache->c_list);
+	spin_lock_init(&cache->c_list_lock);
+	cache->c_hash = kmalloc_array(bucket_count,
+				      sizeof(struct hlist_bl_head),
+				      GFP_KERNEL);
+	if (!cache->c_hash) {
+		kfree(cache);
+		goto err_out;
+	}
+	for (i = 0; i < bucket_count; i++)
+		INIT_HLIST_BL_HEAD(&cache->c_hash[i]);
+
+	cache->c_shrink.count_objects = mb_cache_count;
+	cache->c_shrink.scan_objects = mb_cache_scan;
+	cache->c_shrink.seeks = DEFAULT_SEEKS;
+	if (register_shrinker(&cache->c_shrink)) {
+		kfree(cache->c_hash);
+		kfree(cache);
+		goto err_out;
+	}
+
+	INIT_WORK(&cache->c_shrink_work, mb_cache_shrink_worker);
+
+	return cache;
+
+err_out:
+	return NULL;
+}
+EXPORT_SYMBOL(mb_cache_create);
+
+/*
+ * mb_cache_destroy - destroy cache
+ * @cache: the cache to destroy
+ *
+ * Free all entries in cache and cache itself. Caller must make sure nobody
+ * (except shrinker) can reach @cache when calling this.
+ */
+void mb_cache_destroy(struct mb_cache *cache)
+{
+	struct mb_cache_entry *entry, *next;
+
+	unregister_shrinker(&cache->c_shrink);
+
+	/*
+	 * We don't bother with any locking. Cache must not be used at this
+	 * point.
+	 */
+	list_for_each_entry_safe(entry, next, &cache->c_list, e_list) {
+		list_del(&entry->e_list);
+		WARN_ON(atomic_read(&entry->e_refcnt) != 1);
+		mb_cache_entry_put(cache, entry);
+	}
+	kfree(cache->c_hash);
+	kfree(cache);
+}
+EXPORT_SYMBOL(mb_cache_destroy);
+
+static int __init mbcache_init(void)
+{
+	mb_entry_cache = kmem_cache_create("mbcache",
+				sizeof(struct mb_cache_entry), 0,
+				SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD, NULL);
+	if (!mb_entry_cache)
+		return -ENOMEM;
+	return 0;
+}
+
+static void __exit mbcache_exit(void)
+{
+	kmem_cache_destroy(mb_entry_cache);
+}
+
+module_init(mbcache_init)
+module_exit(mbcache_exit)
+
+MODULE_AUTHOR("Jan Kara <jack@suse.cz>");
+MODULE_DESCRIPTION("Meta block cache (for extended attributes)");
+MODULE_LICENSE("GPL");