dm cache: add cleaner policy
A simple cache policy that writes back all data to the origin.
This is used to decommission a dm cache by emptying it.
Signed-off-by: Heinz Mauelshagen <mauelshagen@redhat.com>
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/dm-cache-policy-cleaner.c b/drivers/md/dm-cache-policy-cleaner.c
new file mode 100644
index 0000000..cc05d70
--- /dev/null
+++ b/drivers/md/dm-cache-policy-cleaner.c
@@ -0,0 +1,464 @@
+/*
+ * Copyright (C) 2012 Red Hat. All rights reserved.
+ *
+ * writeback cache policy supporting flushing out dirty cache blocks.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-cache-policy.h"
+#include "dm.h"
+
+#include <linux/hash.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+
+/*----------------------------------------------------------------*/
+
+#define DM_MSG_PREFIX "cache cleaner"
+#define CLEANER_VERSION "1.0.0"
+
+/* Cache entry struct. */
+struct wb_cache_entry {
+ struct list_head list;
+ struct hlist_node hlist;
+
+ dm_oblock_t oblock;
+ dm_cblock_t cblock;
+ bool dirty:1;
+ bool pending:1;
+};
+
+struct hash {
+ struct hlist_head *table;
+ dm_block_t hash_bits;
+ unsigned nr_buckets;
+};
+
+struct policy {
+ struct dm_cache_policy policy;
+ spinlock_t lock;
+
+ struct list_head free;
+ struct list_head clean;
+ struct list_head clean_pending;
+ struct list_head dirty;
+
+ /*
+ * We know exactly how many cblocks will be needed,
+ * so we can allocate them up front.
+ */
+ dm_cblock_t cache_size, nr_cblocks_allocated;
+ struct wb_cache_entry *cblocks;
+ struct hash chash;
+};
+
+/*----------------------------------------------------------------------------*/
+
+/*
+ * Low-level functions.
+ */
+static unsigned next_power(unsigned n, unsigned min)
+{
+ return roundup_pow_of_two(max(n, min));
+}
+
+static struct policy *to_policy(struct dm_cache_policy *p)
+{
+ return container_of(p, struct policy, policy);
+}
+
+static struct list_head *list_pop(struct list_head *q)
+{
+ struct list_head *r = q->next;
+
+ list_del(r);
+
+ return r;
+}
+
+/*----------------------------------------------------------------------------*/
+
+/* Allocate/free various resources. */
+static int alloc_hash(struct hash *hash, unsigned elts)
+{
+ hash->nr_buckets = next_power(elts >> 4, 16);
+ hash->hash_bits = ffs(hash->nr_buckets) - 1;
+ hash->table = vzalloc(sizeof(*hash->table) * hash->nr_buckets);
+
+ return hash->table ? 0 : -ENOMEM;
+}
+
+static void free_hash(struct hash *hash)
+{
+ vfree(hash->table);
+}
+
+static int alloc_cache_blocks_with_hash(struct policy *p, dm_cblock_t cache_size)
+{
+ int r = -ENOMEM;
+
+ p->cblocks = vzalloc(sizeof(*p->cblocks) * from_cblock(cache_size));
+ if (p->cblocks) {
+ unsigned u = from_cblock(cache_size);
+
+ while (u--)
+ list_add(&p->cblocks[u].list, &p->free);
+
+ p->nr_cblocks_allocated = 0;
+
+ /* Cache entries hash. */
+ r = alloc_hash(&p->chash, from_cblock(cache_size));
+ if (r)
+ vfree(p->cblocks);
+ }
+
+ return r;
+}
+
+static void free_cache_blocks_and_hash(struct policy *p)
+{
+ free_hash(&p->chash);
+ vfree(p->cblocks);
+}
+
+static struct wb_cache_entry *alloc_cache_entry(struct policy *p)
+{
+ struct wb_cache_entry *e;
+
+ BUG_ON(from_cblock(p->nr_cblocks_allocated) >= from_cblock(p->cache_size));
+
+ e = list_entry(list_pop(&p->free), struct wb_cache_entry, list);
+ p->nr_cblocks_allocated = to_cblock(from_cblock(p->nr_cblocks_allocated) + 1);
+
+ return e;
+}
+
+/*----------------------------------------------------------------------------*/
+
+/* Hash functions (lookup, insert, remove). */
+static struct wb_cache_entry *lookup_cache_entry(struct policy *p, dm_oblock_t oblock)
+{
+ struct hash *hash = &p->chash;
+ unsigned h = hash_64(from_oblock(oblock), hash->hash_bits);
+ struct wb_cache_entry *cur;
+ struct hlist_head *bucket = &hash->table[h];
+
+ hlist_for_each_entry(cur, bucket, hlist) {
+ if (cur->oblock == oblock) {
+ /* Move upfront bucket for faster access. */
+ hlist_del(&cur->hlist);
+ hlist_add_head(&cur->hlist, bucket);
+ return cur;
+ }
+ }
+
+ return NULL;
+}
+
+static void insert_cache_hash_entry(struct policy *p, struct wb_cache_entry *e)
+{
+ unsigned h = hash_64(from_oblock(e->oblock), p->chash.hash_bits);
+
+ hlist_add_head(&e->hlist, &p->chash.table[h]);
+}
+
+static void remove_cache_hash_entry(struct wb_cache_entry *e)
+{
+ hlist_del(&e->hlist);
+}
+
+/* Public interface (see dm-cache-policy.h */
+static int wb_map(struct dm_cache_policy *pe, dm_oblock_t oblock,
+ bool can_block, bool can_migrate, bool discarded_oblock,
+ struct bio *bio, struct policy_result *result)
+{
+ struct policy *p = to_policy(pe);
+ struct wb_cache_entry *e;
+ unsigned long flags;
+
+ result->op = POLICY_MISS;
+
+ if (can_block)
+ spin_lock_irqsave(&p->lock, flags);
+
+ else if (!spin_trylock_irqsave(&p->lock, flags))
+ return -EWOULDBLOCK;
+
+ e = lookup_cache_entry(p, oblock);
+ if (e) {
+ result->op = POLICY_HIT;
+ result->cblock = e->cblock;
+
+ }
+
+ spin_unlock_irqrestore(&p->lock, flags);
+
+ return 0;
+}
+
+static int wb_lookup(struct dm_cache_policy *pe, dm_oblock_t oblock, dm_cblock_t *cblock)
+{
+ int r;
+ struct policy *p = to_policy(pe);
+ struct wb_cache_entry *e;
+ unsigned long flags;
+
+ if (!spin_trylock_irqsave(&p->lock, flags))
+ return -EWOULDBLOCK;
+
+ e = lookup_cache_entry(p, oblock);
+ if (e) {
+ *cblock = e->cblock;
+ r = 0;
+
+ } else
+ r = -ENOENT;
+
+ spin_unlock_irqrestore(&p->lock, flags);
+
+ return r;
+}
+
+static void __set_clear_dirty(struct dm_cache_policy *pe, dm_oblock_t oblock, bool set)
+{
+ struct policy *p = to_policy(pe);
+ struct wb_cache_entry *e;
+
+ e = lookup_cache_entry(p, oblock);
+ BUG_ON(!e);
+
+ if (set) {
+ if (!e->dirty) {
+ e->dirty = true;
+ list_move(&e->list, &p->dirty);
+ }
+
+ } else {
+ if (e->dirty) {
+ e->pending = false;
+ e->dirty = false;
+ list_move(&e->list, &p->clean);
+ }
+ }
+}
+
+static void wb_set_dirty(struct dm_cache_policy *pe, dm_oblock_t oblock)
+{
+ struct policy *p = to_policy(pe);
+ unsigned long flags;
+
+ spin_lock_irqsave(&p->lock, flags);
+ __set_clear_dirty(pe, oblock, true);
+ spin_unlock_irqrestore(&p->lock, flags);
+}
+
+static void wb_clear_dirty(struct dm_cache_policy *pe, dm_oblock_t oblock)
+{
+ struct policy *p = to_policy(pe);
+ unsigned long flags;
+
+ spin_lock_irqsave(&p->lock, flags);
+ __set_clear_dirty(pe, oblock, false);
+ spin_unlock_irqrestore(&p->lock, flags);
+}
+
+static void add_cache_entry(struct policy *p, struct wb_cache_entry *e)
+{
+ insert_cache_hash_entry(p, e);
+ if (e->dirty)
+ list_add(&e->list, &p->dirty);
+ else
+ list_add(&e->list, &p->clean);
+}
+
+static int wb_load_mapping(struct dm_cache_policy *pe,
+ dm_oblock_t oblock, dm_cblock_t cblock,
+ uint32_t hint, bool hint_valid)
+{
+ int r;
+ struct policy *p = to_policy(pe);
+ struct wb_cache_entry *e = alloc_cache_entry(p);
+
+ if (e) {
+ e->cblock = cblock;
+ e->oblock = oblock;
+ e->dirty = false; /* blocks default to clean */
+ add_cache_entry(p, e);
+ r = 0;
+
+ } else
+ r = -ENOMEM;
+
+ return r;
+}
+
+static void wb_destroy(struct dm_cache_policy *pe)
+{
+ struct policy *p = to_policy(pe);
+
+ free_cache_blocks_and_hash(p);
+ kfree(p);
+}
+
+static struct wb_cache_entry *__wb_force_remove_mapping(struct policy *p, dm_oblock_t oblock)
+{
+ struct wb_cache_entry *r = lookup_cache_entry(p, oblock);
+
+ BUG_ON(!r);
+
+ remove_cache_hash_entry(r);
+ list_del(&r->list);
+
+ return r;
+}
+
+static void wb_remove_mapping(struct dm_cache_policy *pe, dm_oblock_t oblock)
+{
+ struct policy *p = to_policy(pe);
+ struct wb_cache_entry *e;
+ unsigned long flags;
+
+ spin_lock_irqsave(&p->lock, flags);
+ e = __wb_force_remove_mapping(p, oblock);
+ list_add_tail(&e->list, &p->free);
+ BUG_ON(!from_cblock(p->nr_cblocks_allocated));
+ p->nr_cblocks_allocated = to_cblock(from_cblock(p->nr_cblocks_allocated) - 1);
+ spin_unlock_irqrestore(&p->lock, flags);
+}
+
+static void wb_force_mapping(struct dm_cache_policy *pe,
+ dm_oblock_t current_oblock, dm_oblock_t oblock)
+{
+ struct policy *p = to_policy(pe);
+ struct wb_cache_entry *e;
+ unsigned long flags;
+
+ spin_lock_irqsave(&p->lock, flags);
+ e = __wb_force_remove_mapping(p, current_oblock);
+ e->oblock = oblock;
+ add_cache_entry(p, e);
+ spin_unlock_irqrestore(&p->lock, flags);
+}
+
+static struct wb_cache_entry *get_next_dirty_entry(struct policy *p)
+{
+ struct list_head *l;
+ struct wb_cache_entry *r;
+
+ if (list_empty(&p->dirty))
+ return NULL;
+
+ l = list_pop(&p->dirty);
+ r = container_of(l, struct wb_cache_entry, list);
+ list_add(l, &p->clean_pending);
+
+ return r;
+}
+
+static int wb_writeback_work(struct dm_cache_policy *pe,
+ dm_oblock_t *oblock,
+ dm_cblock_t *cblock)
+{
+ int r = -ENOENT;
+ struct policy *p = to_policy(pe);
+ struct wb_cache_entry *e;
+ unsigned long flags;
+
+ spin_lock_irqsave(&p->lock, flags);
+
+ e = get_next_dirty_entry(p);
+ if (e) {
+ *oblock = e->oblock;
+ *cblock = e->cblock;
+ r = 0;
+ }
+
+ spin_unlock_irqrestore(&p->lock, flags);
+
+ return r;
+}
+
+static dm_cblock_t wb_residency(struct dm_cache_policy *pe)
+{
+ return to_policy(pe)->nr_cblocks_allocated;
+}
+
+/* Init the policy plugin interface function pointers. */
+static void init_policy_functions(struct policy *p)
+{
+ p->policy.destroy = wb_destroy;
+ p->policy.map = wb_map;
+ p->policy.lookup = wb_lookup;
+ p->policy.set_dirty = wb_set_dirty;
+ p->policy.clear_dirty = wb_clear_dirty;
+ p->policy.load_mapping = wb_load_mapping;
+ p->policy.walk_mappings = NULL;
+ p->policy.remove_mapping = wb_remove_mapping;
+ p->policy.writeback_work = wb_writeback_work;
+ p->policy.force_mapping = wb_force_mapping;
+ p->policy.residency = wb_residency;
+ p->policy.tick = NULL;
+}
+
+static struct dm_cache_policy *wb_create(dm_cblock_t cache_size,
+ sector_t origin_size,
+ sector_t cache_block_size)
+{
+ int r;
+ struct policy *p = kzalloc(sizeof(*p), GFP_KERNEL);
+
+ if (!p)
+ return NULL;
+
+ init_policy_functions(p);
+ INIT_LIST_HEAD(&p->free);
+ INIT_LIST_HEAD(&p->clean);
+ INIT_LIST_HEAD(&p->clean_pending);
+ INIT_LIST_HEAD(&p->dirty);
+
+ p->cache_size = cache_size;
+ spin_lock_init(&p->lock);
+
+ /* Allocate cache entry structs and add them to free list. */
+ r = alloc_cache_blocks_with_hash(p, cache_size);
+ if (!r)
+ return &p->policy;
+
+ kfree(p);
+
+ return NULL;
+}
+/*----------------------------------------------------------------------------*/
+
+static struct dm_cache_policy_type wb_policy_type = {
+ .name = "cleaner",
+ .hint_size = 0,
+ .owner = THIS_MODULE,
+ .create = wb_create
+};
+
+static int __init wb_init(void)
+{
+ int r = dm_cache_policy_register(&wb_policy_type);
+
+ if (r < 0)
+ DMERR("register failed %d", r);
+ else
+ DMINFO("version " CLEANER_VERSION " loaded");
+
+ return r;
+}
+
+static void __exit wb_exit(void)
+{
+ dm_cache_policy_unregister(&wb_policy_type);
+}
+
+module_init(wb_init);
+module_exit(wb_exit);
+
+MODULE_AUTHOR("Heinz Mauelshagen <dm-devel@redhat.com>");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("cleaner cache policy");