dm thin: move bio_prison code to separate module

The bio prison code will be useful to other future DM targets so
move it to a separate module.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 415 insertions, 0 deletions

diff --git a/drivers/md/dm-bio-prison.c b/drivers/md/dm-bio-prison.c
new file mode 100644
index 0000000..e4e8415
--- /dev/null
+++ b/drivers/md/dm-bio-prison.c
@@ -0,0 +1,415 @@
+/*
+ * Copyright (C) 2012 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm.h"
+#include "dm-bio-prison.h"
+
+#include <linux/spinlock.h>
+#include <linux/mempool.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+
+/*----------------------------------------------------------------*/
+
+struct dm_bio_prison_cell {
+	struct hlist_node list;
+	struct dm_bio_prison *prison;
+	struct dm_cell_key key;
+	struct bio *holder;
+	struct bio_list bios;
+};
+
+struct dm_bio_prison {
+	spinlock_t lock;
+	mempool_t *cell_pool;
+
+	unsigned nr_buckets;
+	unsigned hash_mask;
+	struct hlist_head *cells;
+};
+
+/*----------------------------------------------------------------*/
+
+static uint32_t calc_nr_buckets(unsigned nr_cells)
+{
+	uint32_t n = 128;
+
+	nr_cells /= 4;
+	nr_cells = min(nr_cells, 8192u);
+
+	while (n < nr_cells)
+		n <<= 1;
+
+	return n;
+}
+
+static struct kmem_cache *_cell_cache;
+
+/*
+ * @nr_cells should be the number of cells you want in use _concurrently_.
+ * Don't confuse it with the number of distinct keys.
+ */
+struct dm_bio_prison *dm_bio_prison_create(unsigned nr_cells)
+{
+	unsigned i;
+	uint32_t nr_buckets = calc_nr_buckets(nr_cells);
+	size_t len = sizeof(struct dm_bio_prison) +
+		(sizeof(struct hlist_head) * nr_buckets);
+	struct dm_bio_prison *prison = kmalloc(len, GFP_KERNEL);
+
+	if (!prison)
+		return NULL;
+
+	spin_lock_init(&prison->lock);
+	prison->cell_pool = mempool_create_slab_pool(nr_cells, _cell_cache);
+	if (!prison->cell_pool) {
+		kfree(prison);
+		return NULL;
+	}
+
+	prison->nr_buckets = nr_buckets;
+	prison->hash_mask = nr_buckets - 1;
+	prison->cells = (struct hlist_head *) (prison + 1);
+	for (i = 0; i < nr_buckets; i++)
+		INIT_HLIST_HEAD(prison->cells + i);
+
+	return prison;
+}
+EXPORT_SYMBOL_GPL(dm_bio_prison_create);
+
+void dm_bio_prison_destroy(struct dm_bio_prison *prison)
+{
+	mempool_destroy(prison->cell_pool);
+	kfree(prison);
+}
+EXPORT_SYMBOL_GPL(dm_bio_prison_destroy);
+
+static uint32_t hash_key(struct dm_bio_prison *prison, struct dm_cell_key *key)
+{
+	const unsigned long BIG_PRIME = 4294967291UL;
+	uint64_t hash = key->block * BIG_PRIME;
+
+	return (uint32_t) (hash & prison->hash_mask);
+}
+
+static int keys_equal(struct dm_cell_key *lhs, struct dm_cell_key *rhs)
+{
+	       return (lhs->virtual == rhs->virtual) &&
+		       (lhs->dev == rhs->dev) &&
+		       (lhs->block == rhs->block);
+}
+
+static struct dm_bio_prison_cell *__search_bucket(struct hlist_head *bucket,
+						  struct dm_cell_key *key)
+{
+	struct dm_bio_prison_cell *cell;
+	struct hlist_node *tmp;
+
+	hlist_for_each_entry(cell, tmp, bucket, list)
+		if (keys_equal(&cell->key, key))
+			return cell;
+
+	return NULL;
+}
+
+/*
+ * This may block if a new cell needs allocating.  You must ensure that
+ * cells will be unlocked even if the calling thread is blocked.
+ *
+ * Returns 1 if the cell was already held, 0 if @inmate is the new holder.
+ */
+int dm_bio_detain(struct dm_bio_prison *prison, struct dm_cell_key *key,
+		  struct bio *inmate, struct dm_bio_prison_cell **ref)
+{
+	int r = 1;
+	unsigned long flags;
+	uint32_t hash = hash_key(prison, key);
+	struct dm_bio_prison_cell *cell, *cell2;
+
+	BUG_ON(hash > prison->nr_buckets);
+
+	spin_lock_irqsave(&prison->lock, flags);
+
+	cell = __search_bucket(prison->cells + hash, key);
+	if (cell) {
+		bio_list_add(&cell->bios, inmate);
+		goto out;
+	}
+
+	/*
+	 * Allocate a new cell
+	 */
+	spin_unlock_irqrestore(&prison->lock, flags);
+	cell2 = mempool_alloc(prison->cell_pool, GFP_NOIO);
+	spin_lock_irqsave(&prison->lock, flags);
+
+	/*
+	 * We've been unlocked, so we have to double check that
+	 * nobody else has inserted this cell in the meantime.
+	 */
+	cell = __search_bucket(prison->cells + hash, key);
+	if (cell) {
+		mempool_free(cell2, prison->cell_pool);
+		bio_list_add(&cell->bios, inmate);
+		goto out;
+	}
+
+	/*
+	 * Use new cell.
+	 */
+	cell = cell2;
+
+	cell->prison = prison;
+	memcpy(&cell->key, key, sizeof(cell->key));
+	cell->holder = inmate;
+	bio_list_init(&cell->bios);
+	hlist_add_head(&cell->list, prison->cells + hash);
+
+	r = 0;
+
+out:
+	spin_unlock_irqrestore(&prison->lock, flags);
+
+	*ref = cell;
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_bio_detain);
+
+/*
+ * @inmates must have been initialised prior to this call
+ */
+static void __cell_release(struct dm_bio_prison_cell *cell, struct bio_list *inmates)
+{
+	struct dm_bio_prison *prison = cell->prison;
+
+	hlist_del(&cell->list);
+
+	if (inmates) {
+		bio_list_add(inmates, cell->holder);
+		bio_list_merge(inmates, &cell->bios);
+	}
+
+	mempool_free(cell, prison->cell_pool);
+}
+
+void dm_cell_release(struct dm_bio_prison_cell *cell, struct bio_list *bios)
+{
+	unsigned long flags;
+	struct dm_bio_prison *prison = cell->prison;
+
+	spin_lock_irqsave(&prison->lock, flags);
+	__cell_release(cell, bios);
+	spin_unlock_irqrestore(&prison->lock, flags);
+}
+EXPORT_SYMBOL_GPL(dm_cell_release);
+
+/*
+ * There are a couple of places where we put a bio into a cell briefly
+ * before taking it out again.  In these situations we know that no other
+ * bio may be in the cell.  This function releases the cell, and also does
+ * a sanity check.
+ */
+static void __cell_release_singleton(struct dm_bio_prison_cell *cell, struct bio *bio)
+{
+	BUG_ON(cell->holder != bio);
+	BUG_ON(!bio_list_empty(&cell->bios));
+
+	__cell_release(cell, NULL);
+}
+
+void dm_cell_release_singleton(struct dm_bio_prison_cell *cell, struct bio *bio)
+{
+	unsigned long flags;
+	struct dm_bio_prison *prison = cell->prison;
+
+	spin_lock_irqsave(&prison->lock, flags);
+	__cell_release_singleton(cell, bio);
+	spin_unlock_irqrestore(&prison->lock, flags);
+}
+EXPORT_SYMBOL_GPL(dm_cell_release_singleton);
+
+/*
+ * Sometimes we don't want the holder, just the additional bios.
+ */
+static void __cell_release_no_holder(struct dm_bio_prison_cell *cell, struct bio_list *inmates)
+{
+	struct dm_bio_prison *prison = cell->prison;
+
+	hlist_del(&cell->list);
+	bio_list_merge(inmates, &cell->bios);
+
+	mempool_free(cell, prison->cell_pool);
+}
+
+void dm_cell_release_no_holder(struct dm_bio_prison_cell *cell, struct bio_list *inmates)
+{
+	unsigned long flags;
+	struct dm_bio_prison *prison = cell->prison;
+
+	spin_lock_irqsave(&prison->lock, flags);
+	__cell_release_no_holder(cell, inmates);
+	spin_unlock_irqrestore(&prison->lock, flags);
+}
+EXPORT_SYMBOL_GPL(dm_cell_release_no_holder);
+
+void dm_cell_error(struct dm_bio_prison_cell *cell)
+{
+	struct dm_bio_prison *prison = cell->prison;
+	struct bio_list bios;
+	struct bio *bio;
+	unsigned long flags;
+
+	bio_list_init(&bios);
+
+	spin_lock_irqsave(&prison->lock, flags);
+	__cell_release(cell, &bios);
+	spin_unlock_irqrestore(&prison->lock, flags);
+
+	while ((bio = bio_list_pop(&bios)))
+		bio_io_error(bio);
+}
+EXPORT_SYMBOL_GPL(dm_cell_error);
+
+/*----------------------------------------------------------------*/
+
+#define DEFERRED_SET_SIZE 64
+
+struct dm_deferred_entry {
+	struct dm_deferred_set *ds;
+	unsigned count;
+	struct list_head work_items;
+};
+
+struct dm_deferred_set {
+	spinlock_t lock;
+	unsigned current_entry;
+	unsigned sweeper;
+	struct dm_deferred_entry entries[DEFERRED_SET_SIZE];
+};
+
+struct dm_deferred_set *dm_deferred_set_create(void)
+{
+	int i;
+	struct dm_deferred_set *ds;
+
+	ds = kmalloc(sizeof(*ds), GFP_KERNEL);
+	if (!ds)
+		return NULL;
+
+	spin_lock_init(&ds->lock);
+	ds->current_entry = 0;
+	ds->sweeper = 0;
+	for (i = 0; i < DEFERRED_SET_SIZE; i++) {
+		ds->entries[i].ds = ds;
+		ds->entries[i].count = 0;
+		INIT_LIST_HEAD(&ds->entries[i].work_items);
+	}
+
+	return ds;
+}
+EXPORT_SYMBOL_GPL(dm_deferred_set_create);
+
+void dm_deferred_set_destroy(struct dm_deferred_set *ds)
+{
+	kfree(ds);
+}
+EXPORT_SYMBOL_GPL(dm_deferred_set_destroy);
+
+struct dm_deferred_entry *dm_deferred_entry_inc(struct dm_deferred_set *ds)
+{
+	unsigned long flags;
+	struct dm_deferred_entry *entry;
+
+	spin_lock_irqsave(&ds->lock, flags);
+	entry = ds->entries + ds->current_entry;
+	entry->count++;
+	spin_unlock_irqrestore(&ds->lock, flags);
+
+	return entry;
+}
+EXPORT_SYMBOL_GPL(dm_deferred_entry_inc);
+
+static unsigned ds_next(unsigned index)
+{
+	return (index + 1) % DEFERRED_SET_SIZE;
+}
+
+static void __sweep(struct dm_deferred_set *ds, struct list_head *head)
+{
+	while ((ds->sweeper != ds->current_entry) &&
+	       !ds->entries[ds->sweeper].count) {
+		list_splice_init(&ds->entries[ds->sweeper].work_items, head);
+		ds->sweeper = ds_next(ds->sweeper);
+	}
+
+	if ((ds->sweeper == ds->current_entry) && !ds->entries[ds->sweeper].count)
+		list_splice_init(&ds->entries[ds->sweeper].work_items, head);
+}
+
+void dm_deferred_entry_dec(struct dm_deferred_entry *entry, struct list_head *head)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&entry->ds->lock, flags);
+	BUG_ON(!entry->count);
+	--entry->count;
+	__sweep(entry->ds, head);
+	spin_unlock_irqrestore(&entry->ds->lock, flags);
+}
+EXPORT_SYMBOL_GPL(dm_deferred_entry_dec);
+
+/*
+ * Returns 1 if deferred or 0 if no pending items to delay job.
+ */
+int dm_deferred_set_add_work(struct dm_deferred_set *ds, struct list_head *work)
+{
+	int r = 1;
+	unsigned long flags;
+	unsigned next_entry;
+
+	spin_lock_irqsave(&ds->lock, flags);
+	if ((ds->sweeper == ds->current_entry) &&
+	    !ds->entries[ds->current_entry].count)
+		r = 0;
+	else {
+		list_add(work, &ds->entries[ds->current_entry].work_items);
+		next_entry = ds_next(ds->current_entry);
+		if (!ds->entries[next_entry].count)
+			ds->current_entry = next_entry;
+	}
+	spin_unlock_irqrestore(&ds->lock, flags);
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_deferred_set_add_work);
+
+/*----------------------------------------------------------------*/
+
+static int __init dm_bio_prison_init(void)
+{
+	_cell_cache = KMEM_CACHE(dm_bio_prison_cell, 0);
+	if (!_cell_cache)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static void __exit dm_bio_prison_exit(void)
+{
+	kmem_cache_destroy(_cell_cache);
+	_cell_cache = NULL;
+}
+
+/*
+ * module hooks
+ */
+module_init(dm_bio_prison_init);
+module_exit(dm_bio_prison_exit);
+
+MODULE_DESCRIPTION(DM_NAME " bio prison");
+MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");
+MODULE_LICENSE("GPL");