dm cache metadata: add "metadata2" feature

If "metadata2" is provided as a table argument when creating/loading a
cache target a more compact metadata format, with separate dirty bits,
is used.  "metadata2" improves speed of shutting down a cache target.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

Documentation/device-mapper/cache.txt

@@ -207,6 +207,10 @@ Optional feature arguments are:
 		   block, then the cache block is invalidated.
 		   To enable passthrough mode the cache must be clean.
 
+   metadata2	: use version 2 of the metadata.  This stores the dirty bits
+                  in a separate btree, which improves speed of shutting
+		  down the cache.
+
 A policy called 'default' is always registered.  This is an alias for
 the policy we currently think is giving best all round performance.
 

drivers/md/dm-cache-metadata.h

@@ -45,18 +45,20 @@
  * As these various flags are defined they should be added to the
  * following masks.
  */
+
 #define DM_CACHE_FEATURE_COMPAT_SUPP	  0UL
 #define DM_CACHE_FEATURE_COMPAT_RO_SUPP	  0UL
 #define DM_CACHE_FEATURE_INCOMPAT_SUPP	  0UL
 
 /*
- * Reopens or creates a new, empty metadata volume.
- * Returns an ERR_PTR on failure.
+ * Reopens or creates a new, empty metadata volume.  Returns an ERR_PTR on
+ * failure.  If reopening then features must match.
  */
 struct dm_cache_metadata *dm_cache_metadata_open(struct block_device *bdev,
 						 sector_t data_block_size,
 						 bool may_format_device,
-						 size_t policy_hint_size);
+						 size_t policy_hint_size,
+						 unsigned metadata_version);
 
 void dm_cache_metadata_close(struct dm_cache_metadata *cmd);
 
@@ -91,7 +93,8 @@ int dm_cache_load_mappings(struct dm_cache_metadata *cmd,
 			   load_mapping_fn fn,
 			   void *context);
 
-int dm_cache_set_dirty(struct dm_cache_metadata *cmd, dm_cblock_t cblock, bool dirty);
+int dm_cache_set_dirty_bits(struct dm_cache_metadata *cmd,
+			    unsigned nr_bits, unsigned long *bits);
 
 struct dm_cache_statistics {
 	uint32_t read_hits;

drivers/md/dm-cache-target.c

@@ -179,6 +179,7 @@ enum cache_io_mode {
 struct cache_features {
 	enum cache_metadata_mode mode;
 	enum cache_io_mode io_mode;
+	unsigned metadata_version;
 };
 
 struct cache_stats {
@@ -2541,13 +2542,14 @@ static void init_features(struct cache_features *cf)
 {
 	cf->mode = CM_WRITE;
 	cf->io_mode = CM_IO_WRITEBACK;
+	cf->metadata_version = 1;
 }
 
 static int parse_features(struct cache_args *ca, struct dm_arg_set *as,
 			  char **error)
 {
 	static struct dm_arg _args[] = {
-		{0, 1, "Invalid number of cache feature arguments"},
+		{0, 2, "Invalid number of cache feature arguments"},
 	};
 
 	int r;
@@ -2573,6 +2575,9 @@ static int parse_features(struct cache_args *ca, struct dm_arg_set *as,
 		else if (!strcasecmp(arg, "passthrough"))
 			cf->io_mode = CM_IO_PASSTHROUGH;
 
+		else if (!strcasecmp(arg, "metadata2"))
+			cf->metadata_version = 2;
+
 		else {
 			*error = "Unrecognised cache feature requested";
 			return -EINVAL;
@@ -2827,7 +2832,8 @@ static int cache_create(struct cache_args *ca, struct cache **result)
 
 	cmd = dm_cache_metadata_open(cache->metadata_dev->bdev,
 				     ca->block_size, may_format,
-				     dm_cache_policy_get_hint_size(cache->policy));
+				     dm_cache_policy_get_hint_size(cache->policy),
+				     ca->features.metadata_version);
 	if (IS_ERR(cmd)) {
 		*error = "Error creating metadata object";
 		r = PTR_ERR(cmd);
@@ -3172,21 +3178,16 @@ static int cache_end_io(struct dm_target *ti, struct bio *bio, int error)
 
 static int write_dirty_bitset(struct cache *cache)
 {
-	unsigned i, r;
+	int r;
 
 	if (get_cache_mode(cache) >= CM_READ_ONLY)
 		return -EINVAL;
 
-	for (i = 0; i < from_cblock(cache->cache_size); i++) {
-		r = dm_cache_set_dirty(cache->cmd, to_cblock(i),
-				       is_dirty(cache, to_cblock(i)));
-		if (r) {
-			metadata_operation_failed(cache, "dm_cache_set_dirty", r);
-			return r;
-		}
-	}
+	r = dm_cache_set_dirty_bits(cache->cmd, from_cblock(cache->cache_size), cache->dirty_bitset);
+	if (r)
+		metadata_operation_failed(cache, "dm_cache_set_dirty_bits", r);
 
-	return 0;
+	return r;
 }
 
 static int write_discard_bitset(struct cache *cache)
@@ -3562,14 +3563,19 @@ static void cache_status(struct dm_target *ti, status_type_t type,
 		       (unsigned) atomic_read(&cache->stats.promotion),
 		       (unsigned long) atomic_read(&cache->nr_dirty));
 
+		if (cache->features.metadata_version == 2)
+			DMEMIT("2 metadata2 ");
+		else
+			DMEMIT("1 ");
+
 		if (writethrough_mode(&cache->features))
-			DMEMIT("1 writethrough ");
+			DMEMIT("writethrough ");
 
 		else if (passthrough_mode(&cache->features))
-			DMEMIT("1 passthrough ");
+			DMEMIT("passthrough ");
 
 		else if (writeback_mode(&cache->features))
-			DMEMIT("1 writeback ");
+			DMEMIT("writeback ");
 
 		else {
 			DMERR("%s: internal error: unknown io mode: %d",
@@ -3817,7 +3823,7 @@ static void cache_io_hints(struct dm_target *ti, struct queue_limits *limits)
 
 static struct target_type cache_target = {
 	.name = "cache",
-	.version = {1, 9, 0},
+	.version = {1, 10, 0},
 	.module = THIS_MODULE,
 	.ctr = cache_ctr,
 	.dtr = cache_dtr,