bcache: A block layer cache

Does writethrough and writeback caching, handles unclean shutdown, and
has a bunch of other nifty features motivated by real world usage.

See the wiki at http://bcache.evilpiepirate.org for more.

Signed-off-by: Kent Overstreet <koverstreet@google.com>

1 files changed, 817 insertions, 0 deletions

diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
new file mode 100644
index 000000000000..5c7e77073b1f
--- /dev/null
+++ b/drivers/md/bcache/sysfs.c
@@ -0,0 +1,817 @@
+/*
+ * bcache sysfs interfaces
+ *
+ * Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
+ * Copyright 2012 Google, Inc.
+ */
+
+#include "bcache.h"
+#include "sysfs.h"
+#include "btree.h"
+#include "request.h"
+
+#include <linux/sort.h>
+
+static const char * const cache_replacement_policies[] = {
+	"lru",
+	"fifo",
+	"random",
+	NULL
+};
+
+write_attribute(attach);
+write_attribute(detach);
+write_attribute(unregister);
+write_attribute(stop);
+write_attribute(clear_stats);
+write_attribute(trigger_gc);
+write_attribute(prune_cache);
+write_attribute(flash_vol_create);
+
+read_attribute(bucket_size);
+read_attribute(block_size);
+read_attribute(nbuckets);
+read_attribute(tree_depth);
+read_attribute(root_usage_percent);
+read_attribute(priority_stats);
+read_attribute(btree_cache_size);
+read_attribute(btree_cache_max_chain);
+read_attribute(cache_available_percent);
+read_attribute(written);
+read_attribute(btree_written);
+read_attribute(metadata_written);
+read_attribute(active_journal_entries);
+
+sysfs_time_stats_attribute(btree_gc,	sec, ms);
+sysfs_time_stats_attribute(btree_split, sec, us);
+sysfs_time_stats_attribute(btree_sort,	ms,  us);
+sysfs_time_stats_attribute(btree_read,	ms,  us);
+sysfs_time_stats_attribute(try_harder,	ms,  us);
+
+read_attribute(btree_nodes);
+read_attribute(btree_used_percent);
+read_attribute(average_key_size);
+read_attribute(dirty_data);
+read_attribute(bset_tree_stats);
+
+read_attribute(state);
+read_attribute(cache_read_races);
+read_attribute(writeback_keys_done);
+read_attribute(writeback_keys_failed);
+read_attribute(io_errors);
+read_attribute(congested);
+rw_attribute(congested_read_threshold_us);
+rw_attribute(congested_write_threshold_us);
+
+rw_attribute(sequential_cutoff);
+rw_attribute(sequential_merge);
+rw_attribute(data_csum);
+rw_attribute(cache_mode);
+rw_attribute(writeback_metadata);
+rw_attribute(writeback_running);
+rw_attribute(writeback_percent);
+rw_attribute(writeback_delay);
+rw_attribute(writeback_rate);
+
+rw_attribute(writeback_rate_update_seconds);
+rw_attribute(writeback_rate_d_term);
+rw_attribute(writeback_rate_p_term_inverse);
+rw_attribute(writeback_rate_d_smooth);
+read_attribute(writeback_rate_debug);
+
+rw_attribute(synchronous);
+rw_attribute(journal_delay_ms);
+rw_attribute(discard);
+rw_attribute(running);
+rw_attribute(label);
+rw_attribute(readahead);
+rw_attribute(io_error_limit);
+rw_attribute(io_error_halflife);
+rw_attribute(verify);
+rw_attribute(key_merging_disabled);
+rw_attribute(gc_always_rewrite);
+rw_attribute(freelist_percent);
+rw_attribute(cache_replacement_policy);
+rw_attribute(btree_shrinker_disabled);
+rw_attribute(copy_gc_enabled);
+rw_attribute(size);
+
+SHOW(__bch_cached_dev)
+{
+	struct cached_dev *dc = container_of(kobj, struct cached_dev,
+					     disk.kobj);
+	const char *states[] = { "no cache", "clean", "dirty", "inconsistent" };
+
+#define var(stat)		(dc->stat)
+
+	if (attr == &sysfs_cache_mode)
+		return snprint_string_list(buf, PAGE_SIZE,
+					   bch_cache_modes + 1,
+					   BDEV_CACHE_MODE(&dc->sb));
+
+	sysfs_printf(data_csum,		"%i", dc->disk.data_csum);
+	var_printf(verify,		"%i");
+	var_printf(writeback_metadata,	"%i");
+	var_printf(writeback_running,	"%i");
+	var_print(writeback_delay);
+	var_print(writeback_percent);
+	sysfs_print(writeback_rate,	dc->writeback_rate.rate);
+
+	var_print(writeback_rate_update_seconds);
+	var_print(writeback_rate_d_term);
+	var_print(writeback_rate_p_term_inverse);
+	var_print(writeback_rate_d_smooth);
+
+	if (attr == &sysfs_writeback_rate_debug) {
+		char dirty[20];
+		char derivative[20];
+		char target[20];
+		hprint(dirty,
+		       atomic_long_read(&dc->disk.sectors_dirty) << 9);
+		hprint(derivative,	dc->writeback_rate_derivative << 9);
+		hprint(target,		dc->writeback_rate_target << 9);
+
+		return sprintf(buf,
+			       "rate:\t\t%u\n"
+			       "change:\t\t%i\n"
+			       "dirty:\t\t%s\n"
+			       "derivative:\t%s\n"
+			       "target:\t\t%s\n",
+			       dc->writeback_rate.rate,
+			       dc->writeback_rate_change,
+			       dirty, derivative, target);
+	}
+
+	sysfs_hprint(dirty_data,
+		     atomic_long_read(&dc->disk.sectors_dirty) << 9);
+
+	var_printf(sequential_merge,	"%i");
+	var_hprint(sequential_cutoff);
+	var_hprint(readahead);
+
+	sysfs_print(running,		atomic_read(&dc->running));
+	sysfs_print(state,		states[BDEV_STATE(&dc->sb)]);
+
+	if (attr == &sysfs_label) {
+		memcpy(buf, dc->sb.label, SB_LABEL_SIZE);
+		buf[SB_LABEL_SIZE + 1] = '\0';
+		strcat(buf, "\n");
+		return strlen(buf);
+	}
+
+#undef var
+	return 0;
+}
+SHOW_LOCKED(bch_cached_dev)
+
+STORE(__cached_dev)
+{
+	struct cached_dev *dc = container_of(kobj, struct cached_dev,
+					     disk.kobj);
+	unsigned v = size;
+	struct cache_set *c;
+
+#define d_strtoul(var)		sysfs_strtoul(var, dc->var)
+#define d_strtoi_h(var)		sysfs_hatoi(var, dc->var)
+
+	sysfs_strtoul(data_csum,	dc->disk.data_csum);
+	d_strtoul(verify);
+	d_strtoul(writeback_metadata);
+	d_strtoul(writeback_running);
+	d_strtoul(writeback_delay);
+	sysfs_strtoul_clamp(writeback_rate,
+			    dc->writeback_rate.rate, 1, 1000000);
+	sysfs_strtoul_clamp(writeback_percent, dc->writeback_percent, 0, 40);
+
+	d_strtoul(writeback_rate_update_seconds);
+	d_strtoul(writeback_rate_d_term);
+	d_strtoul(writeback_rate_p_term_inverse);
+	sysfs_strtoul_clamp(writeback_rate_p_term_inverse,
+			    dc->writeback_rate_p_term_inverse, 1, INT_MAX);
+	d_strtoul(writeback_rate_d_smooth);
+
+	d_strtoul(sequential_merge);
+	d_strtoi_h(sequential_cutoff);
+	d_strtoi_h(readahead);
+
+	if (attr == &sysfs_clear_stats)
+		bch_cache_accounting_clear(&dc->accounting);
+
+	if (attr == &sysfs_running &&
+	    strtoul_or_return(buf))
+		bch_cached_dev_run(dc);
+
+	if (attr == &sysfs_cache_mode) {
+		ssize_t v = read_string_list(buf, bch_cache_modes + 1);
+
+		if (v < 0)
+			return v;
+
+		if ((unsigned) v != BDEV_CACHE_MODE(&dc->sb)) {
+			SET_BDEV_CACHE_MODE(&dc->sb, v);
+			bch_write_bdev_super(dc, NULL);
+		}
+	}
+
+	if (attr == &sysfs_label) {
+		memcpy(dc->sb.label, buf, SB_LABEL_SIZE);
+		bch_write_bdev_super(dc, NULL);
+		if (dc->disk.c) {
+			memcpy(dc->disk.c->uuids[dc->disk.id].label,
+			       buf, SB_LABEL_SIZE);
+			bch_uuid_write(dc->disk.c);
+		}
+	}
+
+	if (attr == &sysfs_attach) {
+		if (parse_uuid(buf, dc->sb.set_uuid) < 16)
+			return -EINVAL;
+
+		list_for_each_entry(c, &bch_cache_sets, list) {
+			v = bch_cached_dev_attach(dc, c);
+			if (!v)
+				return size;
+		}
+
+		pr_err("Can't attach %s: cache set not found", buf);
+		size = v;
+	}
+
+	if (attr == &sysfs_detach && dc->disk.c)
+		bch_cached_dev_detach(dc);
+
+	if (attr == &sysfs_stop)
+		bcache_device_stop(&dc->disk);
+
+	return size;
+}
+
+STORE(bch_cached_dev)
+{
+	struct cached_dev *dc = container_of(kobj, struct cached_dev,
+					     disk.kobj);
+
+	mutex_lock(&bch_register_lock);
+	size = __cached_dev_store(kobj, attr, buf, size);
+
+	if (attr == &sysfs_writeback_running)
+		bch_writeback_queue(dc);
+
+	if (attr == &sysfs_writeback_percent)
+		schedule_delayed_work(&dc->writeback_rate_update,
+				      dc->writeback_rate_update_seconds * HZ);
+
+	mutex_unlock(&bch_register_lock);
+	return size;
+}
+
+static struct attribute *bch_cached_dev_files[] = {
+	&sysfs_attach,
+	&sysfs_detach,
+	&sysfs_stop,
+#if 0
+	&sysfs_data_csum,
+#endif
+	&sysfs_cache_mode,
+	&sysfs_writeback_metadata,
+	&sysfs_writeback_running,
+	&sysfs_writeback_delay,
+	&sysfs_writeback_percent,
+	&sysfs_writeback_rate,
+	&sysfs_writeback_rate_update_seconds,
+	&sysfs_writeback_rate_d_term,
+	&sysfs_writeback_rate_p_term_inverse,
+	&sysfs_writeback_rate_d_smooth,
+	&sysfs_writeback_rate_debug,
+	&sysfs_dirty_data,
+	&sysfs_sequential_cutoff,
+	&sysfs_sequential_merge,
+	&sysfs_clear_stats,
+	&sysfs_running,
+	&sysfs_state,
+	&sysfs_label,
+	&sysfs_readahead,
+#ifdef CONFIG_BCACHE_DEBUG
+	&sysfs_verify,
+#endif
+	NULL
+};
+KTYPE(bch_cached_dev);
+
+SHOW(bch_flash_dev)
+{
+	struct bcache_device *d = container_of(kobj, struct bcache_device,
+					       kobj);
+	struct uuid_entry *u = &d->c->uuids[d->id];
+
+	sysfs_printf(data_csum,	"%i", d->data_csum);
+	sysfs_hprint(size,	u->sectors << 9);
+
+	if (attr == &sysfs_label) {
+		memcpy(buf, u->label, SB_LABEL_SIZE);
+		buf[SB_LABEL_SIZE + 1] = '\0';
+		strcat(buf, "\n");
+		return strlen(buf);
+	}
+
+	return 0;
+}
+
+STORE(__bch_flash_dev)
+{
+	struct bcache_device *d = container_of(kobj, struct bcache_device,
+					       kobj);
+	struct uuid_entry *u = &d->c->uuids[d->id];
+
+	sysfs_strtoul(data_csum,	d->data_csum);
+
+	if (attr == &sysfs_size) {
+		uint64_t v;
+		strtoi_h_or_return(buf, v);
+
+		u->sectors = v >> 9;
+		bch_uuid_write(d->c);
+		set_capacity(d->disk, u->sectors);
+	}
+
+	if (attr == &sysfs_label) {
+		memcpy(u->label, buf, SB_LABEL_SIZE);
+		bch_uuid_write(d->c);
+	}
+
+	if (attr == &sysfs_unregister) {
+		atomic_set(&d->detaching, 1);
+		bcache_device_stop(d);
+	}
+
+	return size;
+}
+STORE_LOCKED(bch_flash_dev)
+
+static struct attribute *bch_flash_dev_files[] = {
+	&sysfs_unregister,
+#if 0
+	&sysfs_data_csum,
+#endif
+	&sysfs_label,
+	&sysfs_size,
+	NULL
+};
+KTYPE(bch_flash_dev);
+
+SHOW(__bch_cache_set)
+{
+	unsigned root_usage(struct cache_set *c)
+	{
+		unsigned bytes = 0;
+		struct bkey *k;
+		struct btree *b;
+		struct btree_iter iter;
+
+		goto lock_root;
+
+		do {
+			rw_unlock(false, b);
+lock_root:
+			b = c->root;
+			rw_lock(false, b, b->level);
+		} while (b != c->root);
+
+		for_each_key_filter(b, k, &iter, bch_ptr_bad)
+			bytes += bkey_bytes(k);
+
+		rw_unlock(false, b);
+
+		return (bytes * 100) / btree_bytes(c);
+	}
+
+	size_t cache_size(struct cache_set *c)
+	{
+		size_t ret = 0;
+		struct btree *b;
+
+		mutex_lock(&c->bucket_lock);
+		list_for_each_entry(b, &c->btree_cache, list)
+			ret += 1 << (b->page_order + PAGE_SHIFT);
+
+		mutex_unlock(&c->bucket_lock);
+		return ret;
+	}
+
+	unsigned cache_max_chain(struct cache_set *c)
+	{
+		unsigned ret = 0;
+		struct hlist_head *h;
+
+		mutex_lock(&c->bucket_lock);
+
+		for (h = c->bucket_hash;
+		     h < c->bucket_hash + (1 << BUCKET_HASH_BITS);
+		     h++) {
+			unsigned i = 0;
+			struct hlist_node *p;
+
+			hlist_for_each(p, h)
+				i++;
+
+			ret = max(ret, i);
+		}
+
+		mutex_unlock(&c->bucket_lock);
+		return ret;
+	}
+
+	unsigned btree_used(struct cache_set *c)
+	{
+		return div64_u64(c->gc_stats.key_bytes * 100,
+				 (c->gc_stats.nodes ?: 1) * btree_bytes(c));
+	}
+
+	unsigned average_key_size(struct cache_set *c)
+	{
+		return c->gc_stats.nkeys
+			? div64_u64(c->gc_stats.data, c->gc_stats.nkeys)
+			: 0;
+	}
+
+	struct cache_set *c = container_of(kobj, struct cache_set, kobj);
+
+	sysfs_print(synchronous,		CACHE_SYNC(&c->sb));
+	sysfs_print(journal_delay_ms,		c->journal_delay_ms);
+	sysfs_hprint(bucket_size,		bucket_bytes(c));
+	sysfs_hprint(block_size,		block_bytes(c));
+	sysfs_print(tree_depth,			c->root->level);
+	sysfs_print(root_usage_percent,		root_usage(c));
+
+	sysfs_hprint(btree_cache_size,		cache_size(c));
+	sysfs_print(btree_cache_max_chain,	cache_max_chain(c));
+	sysfs_print(cache_available_percent,	100 - c->gc_stats.in_use);
+
+	sysfs_print_time_stats(&c->btree_gc_time,	btree_gc, sec, ms);
+	sysfs_print_time_stats(&c->btree_split_time,	btree_split, sec, us);
+	sysfs_print_time_stats(&c->sort_time,		btree_sort, ms, us);
+	sysfs_print_time_stats(&c->btree_read_time,	btree_read, ms, us);
+	sysfs_print_time_stats(&c->try_harder_time,	try_harder, ms, us);
+
+	sysfs_print(btree_used_percent,	btree_used(c));
+	sysfs_print(btree_nodes,	c->gc_stats.nodes);
+	sysfs_hprint(dirty_data,	c->gc_stats.dirty);
+	sysfs_hprint(average_key_size,	average_key_size(c));
+
+	sysfs_print(cache_read_races,
+		    atomic_long_read(&c->cache_read_races));
+
+	sysfs_print(writeback_keys_done,
+		    atomic_long_read(&c->writeback_keys_done));
+	sysfs_print(writeback_keys_failed,
+		    atomic_long_read(&c->writeback_keys_failed));
+
+	/* See count_io_errors for why 88 */
+	sysfs_print(io_error_halflife,	c->error_decay * 88);
+	sysfs_print(io_error_limit,	c->error_limit >> IO_ERROR_SHIFT);
+
+	sysfs_hprint(congested,
+		     ((uint64_t) bch_get_congested(c)) << 9);
+	sysfs_print(congested_read_threshold_us,
+		    c->congested_read_threshold_us);
+	sysfs_print(congested_write_threshold_us,
+		    c->congested_write_threshold_us);
+
+	sysfs_print(active_journal_entries,	fifo_used(&c->journal.pin));
+	sysfs_printf(verify,			"%i", c->verify);
+	sysfs_printf(key_merging_disabled,	"%i", c->key_merging_disabled);
+	sysfs_printf(gc_always_rewrite,		"%i", c->gc_always_rewrite);
+	sysfs_printf(btree_shrinker_disabled,	"%i", c->shrinker_disabled);
+	sysfs_printf(copy_gc_enabled,		"%i", c->copy_gc_enabled);
+
+	if (attr == &sysfs_bset_tree_stats)
+		return bch_bset_print_stats(c, buf);
+
+	return 0;
+}
+SHOW_LOCKED(bch_cache_set)
+
+STORE(__bch_cache_set)
+{
+	struct cache_set *c = container_of(kobj, struct cache_set, kobj);
+
+	if (attr == &sysfs_unregister)
+		bch_cache_set_unregister(c);
+
+	if (attr == &sysfs_stop)
+		bch_cache_set_stop(c);
+
+	if (attr == &sysfs_synchronous) {
+		bool sync = strtoul_or_return(buf);
+
+		if (sync != CACHE_SYNC(&c->sb)) {
+			SET_CACHE_SYNC(&c->sb, sync);
+			bcache_write_super(c);
+		}
+	}
+
+	if (attr == &sysfs_flash_vol_create) {
+		int r;
+		uint64_t v;
+		strtoi_h_or_return(buf, v);
+
+		r = bch_flash_dev_create(c, v);
+		if (r)
+			return r;
+	}
+
+	if (attr == &sysfs_clear_stats) {
+		atomic_long_set(&c->writeback_keys_done,	0);
+		atomic_long_set(&c->writeback_keys_failed,	0);
+
+		memset(&c->gc_stats, 0, sizeof(struct gc_stat));
+		bch_cache_accounting_clear(&c->accounting);
+	}
+
+	if (attr == &sysfs_trigger_gc)
+		bch_queue_gc(c);
+
+	if (attr == &sysfs_prune_cache) {
+		struct shrink_control sc;
+		sc.gfp_mask = GFP_KERNEL;
+		sc.nr_to_scan = strtoul_or_return(buf);
+		c->shrink.shrink(&c->shrink, &sc);
+	}
+
+	sysfs_strtoul(congested_read_threshold_us,
+		      c->congested_read_threshold_us);
+	sysfs_strtoul(congested_write_threshold_us,
+		      c->congested_write_threshold_us);
+
+	if (attr == &sysfs_io_error_limit)
+		c->error_limit = strtoul_or_return(buf) << IO_ERROR_SHIFT;
+
+	/* See count_io_errors() for why 88 */
+	if (attr == &sysfs_io_error_halflife)
+		c->error_decay = strtoul_or_return(buf) / 88;
+
+	sysfs_strtoul(journal_delay_ms,		c->journal_delay_ms);
+	sysfs_strtoul(verify,			c->verify);
+	sysfs_strtoul(key_merging_disabled,	c->key_merging_disabled);
+	sysfs_strtoul(gc_always_rewrite,	c->gc_always_rewrite);
+	sysfs_strtoul(btree_shrinker_disabled,	c->shrinker_disabled);
+	sysfs_strtoul(copy_gc_enabled,		c->copy_gc_enabled);
+
+	return size;
+}
+STORE_LOCKED(bch_cache_set)
+
+SHOW(bch_cache_set_internal)
+{
+	struct cache_set *c = container_of(kobj, struct cache_set, internal);
+	return bch_cache_set_show(&c->kobj, attr, buf);
+}
+
+STORE(bch_cache_set_internal)
+{
+	struct cache_set *c = container_of(kobj, struct cache_set, internal);
+	return bch_cache_set_store(&c->kobj, attr, buf, size);
+}
+
+static void bch_cache_set_internal_release(struct kobject *k)
+{
+}
+
+static struct attribute *bch_cache_set_files[] = {
+	&sysfs_unregister,
+	&sysfs_stop,
+	&sysfs_synchronous,
+	&sysfs_journal_delay_ms,
+	&sysfs_flash_vol_create,
+
+	&sysfs_bucket_size,
+	&sysfs_block_size,
+	&sysfs_tree_depth,
+	&sysfs_root_usage_percent,
+	&sysfs_btree_cache_size,
+	&sysfs_cache_available_percent,
+
+	&sysfs_average_key_size,
+	&sysfs_dirty_data,
+
+	&sysfs_io_error_limit,
+	&sysfs_io_error_halflife,
+	&sysfs_congested,
+	&sysfs_congested_read_threshold_us,
+	&sysfs_congested_write_threshold_us,
+	&sysfs_clear_stats,
+	NULL
+};
+KTYPE(bch_cache_set);
+
+static struct attribute *bch_cache_set_internal_files[] = {
+	&sysfs_active_journal_entries,
+
+	sysfs_time_stats_attribute_list(btree_gc, sec, ms)
+	sysfs_time_stats_attribute_list(btree_split, sec, us)
+	sysfs_time_stats_attribute_list(btree_sort, ms, us)
+	sysfs_time_stats_attribute_list(btree_read, ms, us)
+	sysfs_time_stats_attribute_list(try_harder, ms, us)
+
+	&sysfs_btree_nodes,
+	&sysfs_btree_used_percent,
+	&sysfs_btree_cache_max_chain,
+
+	&sysfs_bset_tree_stats,
+	&sysfs_cache_read_races,
+	&sysfs_writeback_keys_done,
+	&sysfs_writeback_keys_failed,
+
+	&sysfs_trigger_gc,
+	&sysfs_prune_cache,
+#ifdef CONFIG_BCACHE_DEBUG
+	&sysfs_verify,
+	&sysfs_key_merging_disabled,
+#endif
+	&sysfs_gc_always_rewrite,
+	&sysfs_btree_shrinker_disabled,
+	&sysfs_copy_gc_enabled,
+	NULL
+};
+KTYPE(bch_cache_set_internal);
+
+SHOW(__bch_cache)
+{
+	struct cache *ca = container_of(kobj, struct cache, kobj);
+
+	sysfs_hprint(bucket_size,	bucket_bytes(ca));
+	sysfs_hprint(block_size,	block_bytes(ca));
+	sysfs_print(nbuckets,		ca->sb.nbuckets);
+	sysfs_print(discard,		ca->discard);
+	sysfs_hprint(written, atomic_long_read(&ca->sectors_written) << 9);
+	sysfs_hprint(btree_written,
+		     atomic_long_read(&ca->btree_sectors_written) << 9);
+	sysfs_hprint(metadata_written,
+		     (atomic_long_read(&ca->meta_sectors_written) +
+		      atomic_long_read(&ca->btree_sectors_written)) << 9);
+
+	sysfs_print(io_errors,
+		    atomic_read(&ca->io_errors) >> IO_ERROR_SHIFT);
+
+	sysfs_print(freelist_percent, ca->free.size * 100 /
+		    ((size_t) ca->sb.nbuckets));
+
+	if (attr == &sysfs_cache_replacement_policy)
+		return snprint_string_list(buf, PAGE_SIZE,
+					   cache_replacement_policies,
+					   CACHE_REPLACEMENT(&ca->sb));
+
+	if (attr == &sysfs_priority_stats) {
+		int cmp(const void *l, const void *r)
+		{	return *((uint16_t *) r) - *((uint16_t *) l); }
+
+		/* Number of quantiles we compute */
+		const unsigned nq = 31;
+
+		size_t n = ca->sb.nbuckets, i, unused, btree;
+		uint64_t sum = 0;
+		uint16_t q[nq], *p, *cached;
+		ssize_t ret;
+
+		cached = p = vmalloc(ca->sb.nbuckets * sizeof(uint16_t));
+		if (!p)
+			return -ENOMEM;
+
+		mutex_lock(&ca->set->bucket_lock);
+		for (i = ca->sb.first_bucket; i < n; i++)
+			p[i] = ca->buckets[i].prio;
+		mutex_unlock(&ca->set->bucket_lock);
+
+		sort(p, n, sizeof(uint16_t), cmp, NULL);
+
+		while (n &&
+		       !cached[n - 1])
+			--n;
+
+		unused = ca->sb.nbuckets - n;
+
+		while (cached < p + n &&
+		       *cached == BTREE_PRIO)
+			cached++;
+
+		btree = cached - p;
+		n -= btree;
+
+		for (i = 0; i < n; i++)
+			sum += INITIAL_PRIO - cached[i];
+
+		if (n)
+			do_div(sum, n);
+
+		for (i = 0; i < nq; i++)
+			q[i] = INITIAL_PRIO - cached[n * (i + 1) / (nq + 1)];
+
+		vfree(p);
+
+		ret = snprintf(buf, PAGE_SIZE,
+			       "Unused:		%zu%%\n"
+			       "Metadata:	%zu%%\n"
+			       "Average:	%llu\n"
+			       "Sectors per Q:	%zu\n"
+			       "Quantiles:	[",
+			       unused * 100 / (size_t) ca->sb.nbuckets,
+			       btree * 100 / (size_t) ca->sb.nbuckets, sum,
+			       n * ca->sb.bucket_size / (nq + 1));
+
+		for (i = 0; i < nq && ret < (ssize_t) PAGE_SIZE; i++)
+			ret += snprintf(buf + ret, PAGE_SIZE - ret,
+					i < nq - 1 ? "%u " : "%u]\n", q[i]);
+
+		buf[PAGE_SIZE - 1] = '\0';
+		return ret;
+	}
+
+	return 0;
+}
+SHOW_LOCKED(bch_cache)
+
+STORE(__bch_cache)
+{
+	struct cache *ca = container_of(kobj, struct cache, kobj);
+
+	if (attr == &sysfs_discard) {
+		bool v = strtoul_or_return(buf);
+
+		if (blk_queue_discard(bdev_get_queue(ca->bdev)))
+			ca->discard = v;
+
+		if (v != CACHE_DISCARD(&ca->sb)) {
+			SET_CACHE_DISCARD(&ca->sb, v);
+			bcache_write_super(ca->set);
+		}
+	}
+
+	if (attr == &sysfs_cache_replacement_policy) {
+		ssize_t v = read_string_list(buf, cache_replacement_policies);
+
+		if (v < 0)
+			return v;
+
+		if ((unsigned) v != CACHE_REPLACEMENT(&ca->sb)) {
+			mutex_lock(&ca->set->bucket_lock);
+			SET_CACHE_REPLACEMENT(&ca->sb, v);
+			mutex_unlock(&ca->set->bucket_lock);
+
+			bcache_write_super(ca->set);
+		}
+	}
+
+	if (attr == &sysfs_freelist_percent) {
+		DECLARE_FIFO(long, free);
+		long i;
+		size_t p = strtoul_or_return(buf);
+
+		p = clamp_t(size_t,
+			    ((size_t) ca->sb.nbuckets * p) / 100,
+			    roundup_pow_of_two(ca->sb.nbuckets) >> 9,
+			    ca->sb.nbuckets / 2);
+
+		if (!init_fifo_exact(&free, p, GFP_KERNEL))
+			return -ENOMEM;
+
+		mutex_lock(&ca->set->bucket_lock);
+
+		fifo_move(&free, &ca->free);
+		fifo_swap(&free, &ca->free);
+
+		mutex_unlock(&ca->set->bucket_lock);
+
+		while (fifo_pop(&free, i))
+			atomic_dec(&ca->buckets[i].pin);
+
+		free_fifo(&free);
+	}
+
+	if (attr == &sysfs_clear_stats) {
+		atomic_long_set(&ca->sectors_written, 0);
+		atomic_long_set(&ca->btree_sectors_written, 0);
+		atomic_long_set(&ca->meta_sectors_written, 0);
+		atomic_set(&ca->io_count, 0);
+		atomic_set(&ca->io_errors, 0);
+	}
+
+	return size;
+}
+STORE_LOCKED(bch_cache)
+
+static struct attribute *bch_cache_files[] = {
+	&sysfs_bucket_size,
+	&sysfs_block_size,
+	&sysfs_nbuckets,
+	&sysfs_priority_stats,
+	&sysfs_discard,
+	&sysfs_written,
+	&sysfs_btree_written,
+	&sysfs_metadata_written,
+	&sysfs_io_errors,
+	&sysfs_clear_stats,
+	&sysfs_freelist_percent,
+	&sysfs_cache_replacement_policy,
+	NULL
+};
+KTYPE(bch_cache);