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, 1409 insertions, 0 deletions

diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
new file mode 100644
index 00000000000..4f552de49aa
--- /dev/null
+++ b/drivers/md/bcache/request.c
@@ -0,0 +1,1409 @@
+/*
+ * Main bcache entry point - handle a read or a write request and decide what to
+ * do with it; the make_request functions are called by the block layer.
+ *
+ * Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
+ * Copyright 2012 Google, Inc.
+ */
+
+#include "bcache.h"
+#include "btree.h"
+#include "debug.h"
+#include "request.h"
+
+#include <linux/cgroup.h>
+#include <linux/module.h>
+#include <linux/hash.h>
+#include <linux/random.h>
+#include "blk-cgroup.h"
+
+#include <trace/events/bcache.h>
+
+#define CUTOFF_CACHE_ADD	95
+#define CUTOFF_CACHE_READA	90
+#define CUTOFF_WRITEBACK	50
+#define CUTOFF_WRITEBACK_SYNC	75
+
+struct kmem_cache *bch_search_cache;
+
+static void check_should_skip(struct cached_dev *, struct search *);
+
+/* Cgroup interface */
+
+#ifdef CONFIG_CGROUP_BCACHE
+static struct bch_cgroup bcache_default_cgroup = { .cache_mode = -1 };
+
+static struct bch_cgroup *cgroup_to_bcache(struct cgroup *cgroup)
+{
+	struct cgroup_subsys_state *css;
+	return cgroup &&
+		(css = cgroup_subsys_state(cgroup, bcache_subsys_id))
+		? container_of(css, struct bch_cgroup, css)
+		: &bcache_default_cgroup;
+}
+
+struct bch_cgroup *bch_bio_to_cgroup(struct bio *bio)
+{
+	struct cgroup_subsys_state *css = bio->bi_css
+		? cgroup_subsys_state(bio->bi_css->cgroup, bcache_subsys_id)
+		: task_subsys_state(current, bcache_subsys_id);
+
+	return css
+		? container_of(css, struct bch_cgroup, css)
+		: &bcache_default_cgroup;
+}
+
+static ssize_t cache_mode_read(struct cgroup *cgrp, struct cftype *cft,
+			struct file *file,
+			char __user *buf, size_t nbytes, loff_t *ppos)
+{
+	char tmp[1024];
+	int len = snprint_string_list(tmp, PAGE_SIZE, bch_cache_modes,
+				      cgroup_to_bcache(cgrp)->cache_mode + 1);
+
+	if (len < 0)
+		return len;
+
+	return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
+}
+
+static int cache_mode_write(struct cgroup *cgrp, struct cftype *cft,
+			    const char *buf)
+{
+	int v = read_string_list(buf, bch_cache_modes);
+	if (v < 0)
+		return v;
+
+	cgroup_to_bcache(cgrp)->cache_mode = v - 1;
+	return 0;
+}
+
+static u64 bch_verify_read(struct cgroup *cgrp, struct cftype *cft)
+{
+	return cgroup_to_bcache(cgrp)->verify;
+}
+
+static int bch_verify_write(struct cgroup *cgrp, struct cftype *cft, u64 val)
+{
+	cgroup_to_bcache(cgrp)->verify = val;
+	return 0;
+}
+
+static u64 bch_cache_hits_read(struct cgroup *cgrp, struct cftype *cft)
+{
+	struct bch_cgroup *bcachecg = cgroup_to_bcache(cgrp);
+	return atomic_read(&bcachecg->stats.cache_hits);
+}
+
+static u64 bch_cache_misses_read(struct cgroup *cgrp, struct cftype *cft)
+{
+	struct bch_cgroup *bcachecg = cgroup_to_bcache(cgrp);
+	return atomic_read(&bcachecg->stats.cache_misses);
+}
+
+static u64 bch_cache_bypass_hits_read(struct cgroup *cgrp,
+					 struct cftype *cft)
+{
+	struct bch_cgroup *bcachecg = cgroup_to_bcache(cgrp);
+	return atomic_read(&bcachecg->stats.cache_bypass_hits);
+}
+
+static u64 bch_cache_bypass_misses_read(struct cgroup *cgrp,
+					   struct cftype *cft)
+{
+	struct bch_cgroup *bcachecg = cgroup_to_bcache(cgrp);
+	return atomic_read(&bcachecg->stats.cache_bypass_misses);
+}
+
+static struct cftype bch_files[] = {
+	{
+		.name		= "cache_mode",
+		.read		= cache_mode_read,
+		.write_string	= cache_mode_write,
+	},
+	{
+		.name		= "verify",
+		.read_u64	= bch_verify_read,
+		.write_u64	= bch_verify_write,
+	},
+	{
+		.name		= "cache_hits",
+		.read_u64	= bch_cache_hits_read,
+	},
+	{
+		.name		= "cache_misses",
+		.read_u64	= bch_cache_misses_read,
+	},
+	{
+		.name		= "cache_bypass_hits",
+		.read_u64	= bch_cache_bypass_hits_read,
+	},
+	{
+		.name		= "cache_bypass_misses",
+		.read_u64	= bch_cache_bypass_misses_read,
+	},
+	{ }	/* terminate */
+};
+
+static void init_bch_cgroup(struct bch_cgroup *cg)
+{
+	cg->cache_mode = -1;
+}
+
+static struct cgroup_subsys_state *bcachecg_create(struct cgroup *cgroup)
+{
+	struct bch_cgroup *cg;
+
+	cg = kzalloc(sizeof(*cg), GFP_KERNEL);
+	if (!cg)
+		return ERR_PTR(-ENOMEM);
+	init_bch_cgroup(cg);
+	return &cg->css;
+}
+
+static void bcachecg_destroy(struct cgroup *cgroup)
+{
+	struct bch_cgroup *cg = cgroup_to_bcache(cgroup);
+	free_css_id(&bcache_subsys, &cg->css);
+	kfree(cg);
+}
+
+struct cgroup_subsys bcache_subsys = {
+	.create		= bcachecg_create,
+	.destroy	= bcachecg_destroy,
+	.subsys_id	= bcache_subsys_id,
+	.name		= "bcache",
+	.module		= THIS_MODULE,
+};
+EXPORT_SYMBOL_GPL(bcache_subsys);
+#endif
+
+static unsigned cache_mode(struct cached_dev *dc, struct bio *bio)
+{
+#ifdef CONFIG_CGROUP_BCACHE
+	int r = bch_bio_to_cgroup(bio)->cache_mode;
+	if (r >= 0)
+		return r;
+#endif
+	return BDEV_CACHE_MODE(&dc->sb);
+}
+
+static bool verify(struct cached_dev *dc, struct bio *bio)
+{
+#ifdef CONFIG_CGROUP_BCACHE
+	if (bch_bio_to_cgroup(bio)->verify)
+		return true;
+#endif
+	return dc->verify;
+}
+
+static void bio_csum(struct bio *bio, struct bkey *k)
+{
+	struct bio_vec *bv;
+	uint64_t csum = 0;
+	int i;
+
+	bio_for_each_segment(bv, bio, i) {
+		void *d = kmap(bv->bv_page) + bv->bv_offset;
+		csum = crc64_update(csum, d, bv->bv_len);
+		kunmap(bv->bv_page);
+	}
+
+	k->ptr[KEY_PTRS(k)] = csum & (~0ULL >> 1);
+}
+
+/* Insert data into cache */
+
+static void bio_invalidate(struct closure *cl)
+{
+	struct btree_op *op = container_of(cl, struct btree_op, cl);
+	struct bio *bio = op->cache_bio;
+
+	pr_debug("invalidating %i sectors from %llu",
+		 bio_sectors(bio), (uint64_t) bio->bi_sector);
+
+	while (bio_sectors(bio)) {
+		unsigned len = min(bio_sectors(bio), 1U << 14);
+
+		if (bch_keylist_realloc(&op->keys, 0, op->c))
+			goto out;
+
+		bio->bi_sector	+= len;
+		bio->bi_size	-= len << 9;
+
+		bch_keylist_add(&op->keys,
+				&KEY(op->inode, bio->bi_sector, len));
+	}
+
+	op->insert_data_done = true;
+	bio_put(bio);
+out:
+	continue_at(cl, bch_journal, bcache_wq);
+}
+
+struct open_bucket {
+	struct list_head	list;
+	struct task_struct	*last;
+	unsigned		sectors_free;
+	BKEY_PADDED(key);
+};
+
+void bch_open_buckets_free(struct cache_set *c)
+{
+	struct open_bucket *b;
+
+	while (!list_empty(&c->data_buckets)) {
+		b = list_first_entry(&c->data_buckets,
+				     struct open_bucket, list);
+		list_del(&b->list);
+		kfree(b);
+	}
+}
+
+int bch_open_buckets_alloc(struct cache_set *c)
+{
+	int i;
+
+	spin_lock_init(&c->data_bucket_lock);
+
+	for (i = 0; i < 6; i++) {
+		struct open_bucket *b = kzalloc(sizeof(*b), GFP_KERNEL);
+		if (!b)
+			return -ENOMEM;
+
+		list_add(&b->list, &c->data_buckets);
+	}
+
+	return 0;
+}
+
+/*
+ * We keep multiple buckets open for writes, and try to segregate different
+ * write streams for better cache utilization: first we look for a bucket where
+ * the last write to it was sequential with the current write, and failing that
+ * we look for a bucket that was last used by the same task.
+ *
+ * The ideas is if you've got multiple tasks pulling data into the cache at the
+ * same time, you'll get better cache utilization if you try to segregate their
+ * data and preserve locality.
+ *
+ * For example, say you've starting Firefox at the same time you're copying a
+ * bunch of files. Firefox will likely end up being fairly hot and stay in the
+ * cache awhile, but the data you copied might not be; if you wrote all that
+ * data to the same buckets it'd get invalidated at the same time.
+ *
+ * Both of those tasks will be doing fairly random IO so we can't rely on
+ * detecting sequential IO to segregate their data, but going off of the task
+ * should be a sane heuristic.
+ */
+static struct open_bucket *pick_data_bucket(struct cache_set *c,
+					    const struct bkey *search,
+					    struct task_struct *task,
+					    struct bkey *alloc)
+{
+	struct open_bucket *ret, *ret_task = NULL;
+
+	list_for_each_entry_reverse(ret, &c->data_buckets, list)
+		if (!bkey_cmp(&ret->key, search))
+			goto found;
+		else if (ret->last == task)
+			ret_task = ret;
+
+	ret = ret_task ?: list_first_entry(&c->data_buckets,
+					   struct open_bucket, list);
+found:
+	if (!ret->sectors_free && KEY_PTRS(alloc)) {
+		ret->sectors_free = c->sb.bucket_size;
+		bkey_copy(&ret->key, alloc);
+		bkey_init(alloc);
+	}
+
+	if (!ret->sectors_free)
+		ret = NULL;
+
+	return ret;
+}
+
+/*
+ * Allocates some space in the cache to write to, and k to point to the newly
+ * allocated space, and updates KEY_SIZE(k) and KEY_OFFSET(k) (to point to the
+ * end of the newly allocated space).
+ *
+ * May allocate fewer sectors than @sectors, KEY_SIZE(k) indicates how many
+ * sectors were actually allocated.
+ *
+ * If s->writeback is true, will not fail.
+ */
+static bool bch_alloc_sectors(struct bkey *k, unsigned sectors,
+			      struct search *s)
+{
+	struct cache_set *c = s->op.c;
+	struct open_bucket *b;
+	BKEY_PADDED(key) alloc;
+	struct closure cl, *w = NULL;
+	unsigned i;
+
+	if (s->writeback) {
+		closure_init_stack(&cl);
+		w = &cl;
+	}
+
+	/*
+	 * We might have to allocate a new bucket, which we can't do with a
+	 * spinlock held. So if we have to allocate, we drop the lock, allocate
+	 * and then retry. KEY_PTRS() indicates whether alloc points to
+	 * allocated bucket(s).
+	 */
+
+	bkey_init(&alloc.key);
+	spin_lock(&c->data_bucket_lock);
+
+	while (!(b = pick_data_bucket(c, k, s->task, &alloc.key))) {
+		unsigned watermark = s->op.write_prio
+			? WATERMARK_MOVINGGC
+			: WATERMARK_NONE;
+
+		spin_unlock(&c->data_bucket_lock);
+
+		if (bch_bucket_alloc_set(c, watermark, &alloc.key, 1, w))
+			return false;
+
+		spin_lock(&c->data_bucket_lock);
+	}
+
+	/*
+	 * If we had to allocate, we might race and not need to allocate the
+	 * second time we call find_data_bucket(). If we allocated a bucket but
+	 * didn't use it, drop the refcount bch_bucket_alloc_set() took:
+	 */
+	if (KEY_PTRS(&alloc.key))
+		__bkey_put(c, &alloc.key);
+
+	for (i = 0; i < KEY_PTRS(&b->key); i++)
+		EBUG_ON(ptr_stale(c, &b->key, i));
+
+	/* Set up the pointer to the space we're allocating: */
+
+	for (i = 0; i < KEY_PTRS(&b->key); i++)
+		k->ptr[i] = b->key.ptr[i];
+
+	sectors = min(sectors, b->sectors_free);
+
+	SET_KEY_OFFSET(k, KEY_OFFSET(k) + sectors);
+	SET_KEY_SIZE(k, sectors);
+	SET_KEY_PTRS(k, KEY_PTRS(&b->key));
+
+	/*
+	 * Move b to the end of the lru, and keep track of what this bucket was
+	 * last used for:
+	 */
+	list_move_tail(&b->list, &c->data_buckets);
+	bkey_copy_key(&b->key, k);
+	b->last = s->task;
+
+	b->sectors_free	-= sectors;
+
+	for (i = 0; i < KEY_PTRS(&b->key); i++) {
+		SET_PTR_OFFSET(&b->key, i, PTR_OFFSET(&b->key, i) + sectors);
+
+		atomic_long_add(sectors,
+				&PTR_CACHE(c, &b->key, i)->sectors_written);
+	}
+
+	if (b->sectors_free < c->sb.block_size)
+		b->sectors_free = 0;
+
+	/*
+	 * k takes refcounts on the buckets it points to until it's inserted
+	 * into the btree, but if we're done with this bucket we just transfer
+	 * get_data_bucket()'s refcount.
+	 */
+	if (b->sectors_free)
+		for (i = 0; i < KEY_PTRS(&b->key); i++)
+			atomic_inc(&PTR_BUCKET(c, &b->key, i)->pin);
+
+	spin_unlock(&c->data_bucket_lock);
+	return true;
+}
+
+static void bch_insert_data_error(struct closure *cl)
+{
+	struct btree_op *op = container_of(cl, struct btree_op, cl);
+
+	/*
+	 * Our data write just errored, which means we've got a bunch of keys to
+	 * insert that point to data that wasn't succesfully written.
+	 *
+	 * We don't have to insert those keys but we still have to invalidate
+	 * that region of the cache - so, if we just strip off all the pointers
+	 * from the keys we'll accomplish just that.
+	 */
+
+	struct bkey *src = op->keys.bottom, *dst = op->keys.bottom;
+
+	while (src != op->keys.top) {
+		struct bkey *n = bkey_next(src);
+
+		SET_KEY_PTRS(src, 0);
+		bkey_copy(dst, src);
+
+		dst = bkey_next(dst);
+		src = n;
+	}
+
+	op->keys.top = dst;
+
+	bch_journal(cl);
+}
+
+static void bch_insert_data_endio(struct bio *bio, int error)
+{
+	struct closure *cl = bio->bi_private;
+	struct btree_op *op = container_of(cl, struct btree_op, cl);
+	struct search *s = container_of(op, struct search, op);
+
+	if (error) {
+		/* TODO: We could try to recover from this. */
+		if (s->writeback)
+			s->error = error;
+		else if (s->write)
+			set_closure_fn(cl, bch_insert_data_error, bcache_wq);
+		else
+			set_closure_fn(cl, NULL, NULL);
+	}
+
+	bch_bbio_endio(op->c, bio, error, "writing data to cache");
+}
+
+static void bch_insert_data_loop(struct closure *cl)
+{
+	struct btree_op *op = container_of(cl, struct btree_op, cl);
+	struct search *s = container_of(op, struct search, op);
+	struct bio *bio = op->cache_bio, *n;
+
+	if (op->skip)
+		return bio_invalidate(cl);
+
+	if (atomic_sub_return(bio_sectors(bio), &op->c->sectors_to_gc) < 0) {
+		set_gc_sectors(op->c);
+		bch_queue_gc(op->c);
+	}
+
+	do {
+		unsigned i;
+		struct bkey *k;
+		struct bio_set *split = s->d
+			? s->d->bio_split : op->c->bio_split;
+
+		/* 1 for the device pointer and 1 for the chksum */
+		if (bch_keylist_realloc(&op->keys,
+					1 + (op->csum ? 1 : 0),
+					op->c))
+			continue_at(cl, bch_journal, bcache_wq);
+
+		k = op->keys.top;
+		bkey_init(k);
+		SET_KEY_INODE(k, op->inode);
+		SET_KEY_OFFSET(k, bio->bi_sector);
+
+		if (!bch_alloc_sectors(k, bio_sectors(bio), s))
+			goto err;
+
+		n = bch_bio_split(bio, KEY_SIZE(k), GFP_NOIO, split);
+		if (!n) {
+			__bkey_put(op->c, k);
+			continue_at(cl, bch_insert_data_loop, bcache_wq);
+		}
+
+		n->bi_end_io	= bch_insert_data_endio;
+		n->bi_private	= cl;
+
+		if (s->writeback) {
+			SET_KEY_DIRTY(k, true);
+
+			for (i = 0; i < KEY_PTRS(k); i++)
+				SET_GC_MARK(PTR_BUCKET(op->c, k, i),
+					    GC_MARK_DIRTY);
+		}
+
+		SET_KEY_CSUM(k, op->csum);
+		if (KEY_CSUM(k))
+			bio_csum(n, k);
+
+		pr_debug("%s", pkey(k));
+		bch_keylist_push(&op->keys);
+
+		trace_bcache_cache_insert(n, n->bi_sector, n->bi_bdev);
+		n->bi_rw |= REQ_WRITE;
+		bch_submit_bbio(n, op->c, k, 0);
+	} while (n != bio);
+
+	op->insert_data_done = true;
+	continue_at(cl, bch_journal, bcache_wq);
+err:
+	/* bch_alloc_sectors() blocks if s->writeback = true */
+	BUG_ON(s->writeback);
+
+	/*
+	 * But if it's not a writeback write we'd rather just bail out if
+	 * there aren't any buckets ready to write to - it might take awhile and
+	 * we might be starving btree writes for gc or something.
+	 */
+
+	if (s->write) {
+		/*
+		 * Writethrough write: We can't complete the write until we've
+		 * updated the index. But we don't want to delay the write while
+		 * we wait for buckets to be freed up, so just invalidate the
+		 * rest of the write.
+		 */
+		op->skip = true;
+		return bio_invalidate(cl);
+	} else {
+		/*
+		 * From a cache miss, we can just insert the keys for the data
+		 * we have written or bail out if we didn't do anything.
+		 */
+		op->insert_data_done = true;
+		bio_put(bio);
+
+		if (!bch_keylist_empty(&op->keys))
+			continue_at(cl, bch_journal, bcache_wq);
+		else
+			closure_return(cl);
+	}
+}
+
+/**
+ * bch_insert_data - stick some data in the cache
+ *
+ * This is the starting point for any data to end up in a cache device; it could
+ * be from a normal write, or a writeback write, or a write to a flash only
+ * volume - it's also used by the moving garbage collector to compact data in
+ * mostly empty buckets.
+ *
+ * It first writes the data to the cache, creating a list of keys to be inserted
+ * (if the data had to be fragmented there will be multiple keys); after the
+ * data is written it calls bch_journal, and after the keys have been added to
+ * the next journal write they're inserted into the btree.
+ *
+ * It inserts the data in op->cache_bio; bi_sector is used for the key offset,
+ * and op->inode is used for the key inode.
+ *
+ * If op->skip is true, instead of inserting the data it invalidates the region
+ * of the cache represented by op->cache_bio and op->inode.
+ */
+void bch_insert_data(struct closure *cl)
+{
+	struct btree_op *op = container_of(cl, struct btree_op, cl);
+
+	bch_keylist_init(&op->keys);
+	bio_get(op->cache_bio);
+	bch_insert_data_loop(cl);
+}
+
+void bch_btree_insert_async(struct closure *cl)
+{
+	struct btree_op *op = container_of(cl, struct btree_op, cl);
+	struct search *s = container_of(op, struct search, op);
+
+	if (bch_btree_insert(op, op->c)) {
+		s->error		= -ENOMEM;
+		op->insert_data_done	= true;
+	}
+
+	if (op->insert_data_done) {
+		bch_keylist_free(&op->keys);
+		closure_return(cl);
+	} else
+		continue_at(cl, bch_insert_data_loop, bcache_wq);
+}
+
+/* Common code for the make_request functions */
+
+static void request_endio(struct bio *bio, int error)
+{
+	struct closure *cl = bio->bi_private;
+
+	if (error) {
+		struct search *s = container_of(cl, struct search, cl);
+		s->error = error;
+		/* Only cache read errors are recoverable */
+		s->recoverable = false;
+	}
+
+	bio_put(bio);
+	closure_put(cl);
+}
+
+void bch_cache_read_endio(struct bio *bio, int error)
+{
+	struct bbio *b = container_of(bio, struct bbio, bio);
+	struct closure *cl = bio->bi_private;
+	struct search *s = container_of(cl, struct search, cl);
+
+	/*
+	 * If the bucket was reused while our bio was in flight, we might have
+	 * read the wrong data. Set s->error but not error so it doesn't get
+	 * counted against the cache device, but we'll still reread the data
+	 * from the backing device.
+	 */
+
+	if (error)
+		s->error = error;
+	else if (ptr_stale(s->op.c, &b->key, 0)) {
+		atomic_long_inc(&s->op.c->cache_read_races);
+		s->error = -EINTR;
+	}
+
+	bch_bbio_endio(s->op.c, bio, error, "reading from cache");
+}
+
+static void bio_complete(struct search *s)
+{
+	if (s->orig_bio) {
+		int cpu, rw = bio_data_dir(s->orig_bio);
+		unsigned long duration = jiffies - s->start_time;
+
+		cpu = part_stat_lock();
+		part_round_stats(cpu, &s->d->disk->part0);
+		part_stat_add(cpu, &s->d->disk->part0, ticks[rw], duration);
+		part_stat_unlock();
+
+		trace_bcache_request_end(s, s->orig_bio);
+		bio_endio(s->orig_bio, s->error);
+		s->orig_bio = NULL;
+	}
+}
+
+static void do_bio_hook(struct search *s)
+{
+	struct bio *bio = &s->bio.bio;
+	memcpy(bio, s->orig_bio, sizeof(struct bio));
+
+	bio->bi_end_io		= request_endio;
+	bio->bi_private		= &s->cl;
+	atomic_set(&bio->bi_cnt, 3);
+}
+
+static void search_free(struct closure *cl)
+{
+	struct search *s = container_of(cl, struct search, cl);
+	bio_complete(s);
+
+	if (s->op.cache_bio)
+		bio_put(s->op.cache_bio);
+
+	if (s->unaligned_bvec)
+		mempool_free(s->bio.bio.bi_io_vec, s->d->unaligned_bvec);
+
+	closure_debug_destroy(cl);
+	mempool_free(s, s->d->c->search);
+}
+
+static struct search *search_alloc(struct bio *bio, struct bcache_device *d)
+{
+	struct bio_vec *bv;
+	struct search *s = mempool_alloc(d->c->search, GFP_NOIO);
+	memset(s, 0, offsetof(struct search, op.keys));
+
+	__closure_init(&s->cl, NULL);
+
+	s->op.inode		= d->id;
+	s->op.c			= d->c;
+	s->d			= d;
+	s->op.lock		= -1;
+	s->task			= current;
+	s->orig_bio		= bio;
+	s->write		= (bio->bi_rw & REQ_WRITE) != 0;
+	s->op.flush_journal	= (bio->bi_rw & REQ_FLUSH) != 0;
+	s->op.skip		= (bio->bi_rw & REQ_DISCARD) != 0;
+	s->recoverable		= 1;
+	s->start_time		= jiffies;
+	do_bio_hook(s);
+
+	if (bio->bi_size != bio_segments(bio) * PAGE_SIZE) {
+		bv = mempool_alloc(d->unaligned_bvec, GFP_NOIO);
+		memcpy(bv, bio_iovec(bio),
+		       sizeof(struct bio_vec) * bio_segments(bio));
+
+		s->bio.bio.bi_io_vec	= bv;
+		s->unaligned_bvec	= 1;
+	}
+
+	return s;
+}
+
+static void btree_read_async(struct closure *cl)
+{
+	struct btree_op *op = container_of(cl, struct btree_op, cl);
+
+	int ret = btree_root(search_recurse, op->c, op);
+
+	if (ret == -EAGAIN)
+		continue_at(cl, btree_read_async, bcache_wq);
+
+	closure_return(cl);
+}
+
+/* Cached devices */
+
+static void cached_dev_bio_complete(struct closure *cl)
+{
+	struct search *s = container_of(cl, struct search, cl);
+	struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);
+
+	search_free(cl);
+	cached_dev_put(dc);
+}
+
+/* Process reads */
+
+static void cached_dev_read_complete(struct closure *cl)
+{
+	struct search *s = container_of(cl, struct search, cl);
+
+	if (s->op.insert_collision)
+		bch_mark_cache_miss_collision(s);
+
+	if (s->op.cache_bio) {
+		int i;
+		struct bio_vec *bv;
+
+		__bio_for_each_segment(bv, s->op.cache_bio, i, 0)
+			__free_page(bv->bv_page);
+	}
+
+	cached_dev_bio_complete(cl);
+}
+
+static void request_read_error(struct closure *cl)
+{
+	struct search *s = container_of(cl, struct search, cl);
+	struct bio_vec *bv;
+	int i;
+
+	if (s->recoverable) {
+		/* The cache read failed, but we can retry from the backing
+		 * device.
+		 */
+		pr_debug("recovering at sector %llu",
+			 (uint64_t) s->orig_bio->bi_sector);
+
+		s->error = 0;
+		bv = s->bio.bio.bi_io_vec;
+		do_bio_hook(s);
+		s->bio.bio.bi_io_vec = bv;
+
+		if (!s->unaligned_bvec)
+			bio_for_each_segment(bv, s->orig_bio, i)
+				bv->bv_offset = 0, bv->bv_len = PAGE_SIZE;
+		else
+			memcpy(s->bio.bio.bi_io_vec,
+			       bio_iovec(s->orig_bio),
+			       sizeof(struct bio_vec) *
+			       bio_segments(s->orig_bio));
+
+		/* XXX: invalidate cache */
+
+		trace_bcache_read_retry(&s->bio.bio);
+		closure_bio_submit(&s->bio.bio, &s->cl, s->d);
+	}
+
+	continue_at(cl, cached_dev_read_complete, NULL);
+}
+
+static void request_read_done(struct closure *cl)
+{
+	struct search *s = container_of(cl, struct search, cl);
+	struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);
+
+	/*
+	 * s->cache_bio != NULL implies that we had a cache miss; cache_bio now
+	 * contains data ready to be inserted into the cache.
+	 *
+	 * First, we copy the data we just read from cache_bio's bounce buffers
+	 * to the buffers the original bio pointed to:
+	 */
+
+	if (s->op.cache_bio) {
+		struct bio_vec *src, *dst;
+		unsigned src_offset, dst_offset, bytes;
+		void *dst_ptr;
+
+		bio_reset(s->op.cache_bio);
+		s->op.cache_bio->bi_sector	= s->cache_miss->bi_sector;
+		s->op.cache_bio->bi_bdev	= s->cache_miss->bi_bdev;
+		s->op.cache_bio->bi_size	= s->cache_bio_sectors << 9;
+		bio_map(s->op.cache_bio, NULL);
+
+		src = bio_iovec(s->op.cache_bio);
+		dst = bio_iovec(s->cache_miss);
+		src_offset = src->bv_offset;
+		dst_offset = dst->bv_offset;
+		dst_ptr = kmap(dst->bv_page);
+
+		while (1) {
+			if (dst_offset == dst->bv_offset + dst->bv_len) {
+				kunmap(dst->bv_page);
+				dst++;
+				if (dst == bio_iovec_idx(s->cache_miss,
+						s->cache_miss->bi_vcnt))
+					break;
+
+				dst_offset = dst->bv_offset;
+				dst_ptr = kmap(dst->bv_page);
+			}
+
+			if (src_offset == src->bv_offset + src->bv_len) {
+				src++;
+				if (src == bio_iovec_idx(s->op.cache_bio,
+						 s->op.cache_bio->bi_vcnt))
+					BUG();
+
+				src_offset = src->bv_offset;
+			}
+
+			bytes = min(dst->bv_offset + dst->bv_len - dst_offset,
+				    src->bv_offset + src->bv_len - src_offset);
+
+			memcpy(dst_ptr + dst_offset,
+			       page_address(src->bv_page) + src_offset,
+			       bytes);
+
+			src_offset	+= bytes;
+			dst_offset	+= bytes;
+		}
+
+		bio_put(s->cache_miss);
+		s->cache_miss = NULL;
+	}
+
+	if (verify(dc, &s->bio.bio) && s->recoverable)
+		bch_data_verify(s);
+
+	bio_complete(s);
+
+	if (s->op.cache_bio &&
+	    !test_bit(CACHE_SET_STOPPING, &s->op.c->flags)) {
+		s->op.type = BTREE_REPLACE;
+		closure_call(&s->op.cl, bch_insert_data, NULL, cl);
+	}
+
+	continue_at(cl, cached_dev_read_complete, NULL);
+}
+
+static void request_read_done_bh(struct closure *cl)
+{
+	struct search *s = container_of(cl, struct search, cl);
+	struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);
+
+	bch_mark_cache_accounting(s, !s->cache_miss, s->op.skip);
+
+	if (s->error)
+		continue_at_nobarrier(cl, request_read_error, bcache_wq);
+	else if (s->op.cache_bio || verify(dc, &s->bio.bio))
+		continue_at_nobarrier(cl, request_read_done, bcache_wq);
+	else
+		continue_at_nobarrier(cl, cached_dev_read_complete, NULL);
+}
+
+static int cached_dev_cache_miss(struct btree *b, struct search *s,
+				 struct bio *bio, unsigned sectors)
+{
+	int ret = 0;
+	unsigned reada;
+	struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);
+	struct bio *miss;
+
+	miss = bch_bio_split(bio, sectors, GFP_NOIO, s->d->bio_split);
+	if (!miss)
+		return -EAGAIN;
+
+	if (miss == bio)
+		s->op.lookup_done = true;
+
+	miss->bi_end_io		= request_endio;
+	miss->bi_private	= &s->cl;
+
+	if (s->cache_miss || s->op.skip)
+		goto out_submit;
+
+	if (miss != bio ||
+	    (bio->bi_rw & REQ_RAHEAD) ||
+	    (bio->bi_rw & REQ_META) ||
+	    s->op.c->gc_stats.in_use >= CUTOFF_CACHE_READA)
+		reada = 0;
+	else {
+		reada = min(dc->readahead >> 9,
+			    sectors - bio_sectors(miss));
+
+		if (bio_end(miss) + reada > bdev_sectors(miss->bi_bdev))
+			reada = bdev_sectors(miss->bi_bdev) - bio_end(miss);
+	}
+
+	s->cache_bio_sectors = bio_sectors(miss) + reada;
+	s->op.cache_bio = bio_alloc_bioset(GFP_NOWAIT,
+			DIV_ROUND_UP(s->cache_bio_sectors, PAGE_SECTORS),
+			dc->disk.bio_split);
+
+	if (!s->op.cache_bio)
+		goto out_submit;
+
+	s->op.cache_bio->bi_sector	= miss->bi_sector;
+	s->op.cache_bio->bi_bdev	= miss->bi_bdev;
+	s->op.cache_bio->bi_size	= s->cache_bio_sectors << 9;
+
+	s->op.cache_bio->bi_end_io	= request_endio;
+	s->op.cache_bio->bi_private	= &s->cl;
+
+	/* btree_search_recurse()'s btree iterator is no good anymore */
+	ret = -EINTR;
+	if (!bch_btree_insert_check_key(b, &s->op, s->op.cache_bio))
+		goto out_put;
+
+	bio_map(s->op.cache_bio, NULL);
+	if (bio_alloc_pages(s->op.cache_bio, __GFP_NOWARN|GFP_NOIO))
+		goto out_put;
+
+	s->cache_miss = miss;
+	bio_get(s->op.cache_bio);
+
+	trace_bcache_cache_miss(s->orig_bio);
+	closure_bio_submit(s->op.cache_bio, &s->cl, s->d);
+
+	return ret;
+out_put:
+	bio_put(s->op.cache_bio);
+	s->op.cache_bio = NULL;
+out_submit:
+	closure_bio_submit(miss, &s->cl, s->d);
+	return ret;
+}
+
+static void request_read(struct cached_dev *dc, struct search *s)
+{
+	struct closure *cl = &s->cl;
+
+	check_should_skip(dc, s);
+	closure_call(&s->op.cl, btree_read_async, NULL, cl);
+
+	continue_at(cl, request_read_done_bh, NULL);
+}
+
+/* Process writes */
+
+static void cached_dev_write_complete(struct closure *cl)
+{
+	struct search *s = container_of(cl, struct search, cl);
+	struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);
+
+	up_read_non_owner(&dc->writeback_lock);
+	cached_dev_bio_complete(cl);
+}
+
+static bool should_writeback(struct cached_dev *dc, struct bio *bio)
+{
+	unsigned threshold = (bio->bi_rw & REQ_SYNC)
+		? CUTOFF_WRITEBACK_SYNC
+		: CUTOFF_WRITEBACK;
+
+	return !atomic_read(&dc->disk.detaching) &&
+		cache_mode(dc, bio) == CACHE_MODE_WRITEBACK &&
+		dc->disk.c->gc_stats.in_use < threshold;
+}
+
+static void request_write(struct cached_dev *dc, struct search *s)
+{
+	struct closure *cl = &s->cl;
+	struct bio *bio = &s->bio.bio;
+	struct bkey start, end;
+	start = KEY(dc->disk.id, bio->bi_sector, 0);
+	end = KEY(dc->disk.id, bio_end(bio), 0);
+
+	bch_keybuf_check_overlapping(&s->op.c->moving_gc_keys, &start, &end);
+
+	check_should_skip(dc, s);
+	down_read_non_owner(&dc->writeback_lock);
+
+	if (bch_keybuf_check_overlapping(&dc->writeback_keys, &start, &end)) {
+		s->op.skip	= false;
+		s->writeback	= true;
+	}
+
+	if (bio->bi_rw & REQ_DISCARD)
+		goto skip;
+
+	if (s->op.skip)
+		goto skip;
+
+	if (should_writeback(dc, s->orig_bio))
+		s->writeback = true;
+
+	if (!s->writeback) {
+		s->op.cache_bio = bio_clone_bioset(bio, GFP_NOIO,
+						   dc->disk.bio_split);
+
+		trace_bcache_writethrough(s->orig_bio);
+		closure_bio_submit(bio, cl, s->d);
+	} else {
+		s->op.cache_bio = bio;
+		trace_bcache_writeback(s->orig_bio);
+		bch_writeback_add(dc, bio_sectors(bio));
+	}
+out:
+	closure_call(&s->op.cl, bch_insert_data, NULL, cl);
+	continue_at(cl, cached_dev_write_complete, NULL);
+skip:
+	s->op.skip = true;
+	s->op.cache_bio = s->orig_bio;
+	bio_get(s->op.cache_bio);
+	trace_bcache_write_skip(s->orig_bio);
+
+	if ((bio->bi_rw & REQ_DISCARD) &&
+	    !blk_queue_discard(bdev_get_queue(dc->bdev)))
+		goto out;
+
+	closure_bio_submit(bio, cl, s->d);
+	goto out;
+}
+
+static void request_nodata(struct cached_dev *dc, struct search *s)
+{
+	struct closure *cl = &s->cl;
+	struct bio *bio = &s->bio.bio;
+
+	if (bio->bi_rw & REQ_DISCARD) {
+		request_write(dc, s);
+		return;
+	}
+
+	if (s->op.flush_journal)
+		bch_journal_meta(s->op.c, cl);
+
+	closure_bio_submit(bio, cl, s->d);
+
+	continue_at(cl, cached_dev_bio_complete, NULL);
+}
+
+/* Cached devices - read & write stuff */
+
+int bch_get_congested(struct cache_set *c)
+{
+	int i;
+
+	if (!c->congested_read_threshold_us &&
+	    !c->congested_write_threshold_us)
+		return 0;
+
+	i = (local_clock_us() - c->congested_last_us) / 1024;
+	if (i < 0)
+		return 0;
+
+	i += atomic_read(&c->congested);
+	if (i >= 0)
+		return 0;
+
+	i += CONGESTED_MAX;
+
+	return i <= 0 ? 1 : fract_exp_two(i, 6);
+}
+
+static void add_sequential(struct task_struct *t)
+{
+	ewma_add(t->sequential_io_avg,
+		 t->sequential_io, 8, 0);
+
+	t->sequential_io = 0;
+}
+
+static void check_should_skip(struct cached_dev *dc, struct search *s)
+{
+	struct hlist_head *iohash(uint64_t k)
+	{ return &dc->io_hash[hash_64(k, RECENT_IO_BITS)]; }
+
+	struct cache_set *c = s->op.c;
+	struct bio *bio = &s->bio.bio;
+
+	long rand;
+	int cutoff = bch_get_congested(c);
+	unsigned mode = cache_mode(dc, bio);
+
+	if (atomic_read(&dc->disk.detaching) ||
+	    c->gc_stats.in_use > CUTOFF_CACHE_ADD ||
+	    (bio->bi_rw & REQ_DISCARD))
+		goto skip;
+
+	if (mode == CACHE_MODE_NONE ||
+	    (mode == CACHE_MODE_WRITEAROUND &&
+	     (bio->bi_rw & REQ_WRITE)))
+		goto skip;
+
+	if (bio->bi_sector   & (c->sb.block_size - 1) ||
+	    bio_sectors(bio) & (c->sb.block_size - 1)) {
+		pr_debug("skipping unaligned io");
+		goto skip;
+	}
+
+	if (!cutoff) {
+		cutoff = dc->sequential_cutoff >> 9;
+
+		if (!cutoff)
+			goto rescale;
+
+		if (mode == CACHE_MODE_WRITEBACK &&
+		    (bio->bi_rw & REQ_WRITE) &&
+		    (bio->bi_rw & REQ_SYNC))
+			goto rescale;
+	}
+
+	if (dc->sequential_merge) {
+		struct io *i;
+
+		spin_lock(&dc->io_lock);
+
+		hlist_for_each_entry(i, iohash(bio->bi_sector), hash)
+			if (i->last == bio->bi_sector &&
+			    time_before(jiffies, i->jiffies))
+				goto found;
+
+		i = list_first_entry(&dc->io_lru, struct io, lru);
+
+		add_sequential(s->task);
+		i->sequential = 0;
+found:
+		if (i->sequential + bio->bi_size > i->sequential)
+			i->sequential	+= bio->bi_size;
+
+		i->last			 = bio_end(bio);
+		i->jiffies		 = jiffies + msecs_to_jiffies(5000);
+		s->task->sequential_io	 = i->sequential;
+
+		hlist_del(&i->hash);
+		hlist_add_head(&i->hash, iohash(i->last));
+		list_move_tail(&i->lru, &dc->io_lru);
+
+		spin_unlock(&dc->io_lock);
+	} else {
+		s->task->sequential_io = bio->bi_size;
+
+		add_sequential(s->task);
+	}
+
+	rand = get_random_int();
+	cutoff -= bitmap_weight(&rand, BITS_PER_LONG);
+
+	if (cutoff <= (int) (max(s->task->sequential_io,
+				 s->task->sequential_io_avg) >> 9))
+		goto skip;
+
+rescale:
+	bch_rescale_priorities(c, bio_sectors(bio));
+	return;
+skip:
+	bch_mark_sectors_bypassed(s, bio_sectors(bio));
+	s->op.skip = true;
+}
+
+static void cached_dev_make_request(struct request_queue *q, struct bio *bio)
+{
+	struct search *s;
+	struct bcache_device *d = bio->bi_bdev->bd_disk->private_data;
+	struct cached_dev *dc = container_of(d, struct cached_dev, disk);
+	int cpu, rw = bio_data_dir(bio);
+
+	cpu = part_stat_lock();
+	part_stat_inc(cpu, &d->disk->part0, ios[rw]);
+	part_stat_add(cpu, &d->disk->part0, sectors[rw], bio_sectors(bio));
+	part_stat_unlock();
+
+	bio->bi_bdev = dc->bdev;
+	bio->bi_sector += BDEV_DATA_START;
+
+	if (cached_dev_get(dc)) {
+		s = search_alloc(bio, d);
+		trace_bcache_request_start(s, bio);
+
+		if (!bio_has_data(bio))
+			request_nodata(dc, s);
+		else if (rw)
+			request_write(dc, s);
+		else
+			request_read(dc, s);
+	} else {
+		if ((bio->bi_rw & REQ_DISCARD) &&
+		    !blk_queue_discard(bdev_get_queue(dc->bdev)))
+			bio_endio(bio, 0);
+		else
+			bch_generic_make_request(bio, &d->bio_split_hook);
+	}
+}
+
+static int cached_dev_ioctl(struct bcache_device *d, fmode_t mode,
+			    unsigned int cmd, unsigned long arg)
+{
+	struct cached_dev *dc = container_of(d, struct cached_dev, disk);
+	return __blkdev_driver_ioctl(dc->bdev, mode, cmd, arg);
+}
+
+static int cached_dev_congested(void *data, int bits)
+{
+	struct bcache_device *d = data;
+	struct cached_dev *dc = container_of(d, struct cached_dev, disk);
+	struct request_queue *q = bdev_get_queue(dc->bdev);
+	int ret = 0;
+
+	if (bdi_congested(&q->backing_dev_info, bits))
+		return 1;
+
+	if (cached_dev_get(dc)) {
+		unsigned i;
+		struct cache *ca;
+
+		for_each_cache(ca, d->c, i) {
+			q = bdev_get_queue(ca->bdev);
+			ret |= bdi_congested(&q->backing_dev_info, bits);
+		}
+
+		cached_dev_put(dc);
+	}
+
+	return ret;
+}
+
+void bch_cached_dev_request_init(struct cached_dev *dc)
+{
+	struct gendisk *g = dc->disk.disk;
+
+	g->queue->make_request_fn		= cached_dev_make_request;
+	g->queue->backing_dev_info.congested_fn = cached_dev_congested;
+	dc->disk.cache_miss			= cached_dev_cache_miss;
+	dc->disk.ioctl				= cached_dev_ioctl;
+}
+
+/* Flash backed devices */
+
+static int flash_dev_cache_miss(struct btree *b, struct search *s,
+				struct bio *bio, unsigned sectors)
+{
+	/* Zero fill bio */
+
+	while (bio->bi_idx != bio->bi_vcnt) {
+		struct bio_vec *bv = bio_iovec(bio);
+		unsigned j = min(bv->bv_len >> 9, sectors);
+
+		void *p = kmap(bv->bv_page);
+		memset(p + bv->bv_offset, 0, j << 9);
+		kunmap(bv->bv_page);
+
+		bv->bv_len	-= j << 9;
+		bv->bv_offset	+= j << 9;
+
+		if (bv->bv_len)
+			return 0;
+
+		bio->bi_sector	+= j;
+		bio->bi_size	-= j << 9;
+
+		bio->bi_idx++;
+		sectors		-= j;
+	}
+
+	s->op.lookup_done = true;
+
+	return 0;
+}
+
+static void flash_dev_make_request(struct request_queue *q, struct bio *bio)
+{
+	struct search *s;
+	struct closure *cl;
+	struct bcache_device *d = bio->bi_bdev->bd_disk->private_data;
+	int cpu, rw = bio_data_dir(bio);
+
+	cpu = part_stat_lock();
+	part_stat_inc(cpu, &d->disk->part0, ios[rw]);
+	part_stat_add(cpu, &d->disk->part0, sectors[rw], bio_sectors(bio));
+	part_stat_unlock();
+
+	s = search_alloc(bio, d);
+	cl = &s->cl;
+	bio = &s->bio.bio;
+
+	trace_bcache_request_start(s, bio);
+
+	if (bio_has_data(bio) && !rw) {
+		closure_call(&s->op.cl, btree_read_async, NULL, cl);
+	} else if (bio_has_data(bio) || s->op.skip) {
+		bch_keybuf_check_overlapping(&s->op.c->moving_gc_keys,
+					     &KEY(d->id, bio->bi_sector, 0),
+					     &KEY(d->id, bio_end(bio), 0));
+
+		s->writeback	= true;
+		s->op.cache_bio	= bio;
+
+		closure_call(&s->op.cl, bch_insert_data, NULL, cl);
+	} else {
+		/* No data - probably a cache flush */
+		if (s->op.flush_journal)
+			bch_journal_meta(s->op.c, cl);
+	}
+
+	continue_at(cl, search_free, NULL);
+}
+
+static int flash_dev_ioctl(struct bcache_device *d, fmode_t mode,
+			   unsigned int cmd, unsigned long arg)
+{
+	return -ENOTTY;
+}
+
+static int flash_dev_congested(void *data, int bits)
+{
+	struct bcache_device *d = data;
+	struct request_queue *q;
+	struct cache *ca;
+	unsigned i;
+	int ret = 0;
+
+	for_each_cache(ca, d->c, i) {
+		q = bdev_get_queue(ca->bdev);
+		ret |= bdi_congested(&q->backing_dev_info, bits);
+	}
+
+	return ret;
+}
+
+void bch_flash_dev_request_init(struct bcache_device *d)
+{
+	struct gendisk *g = d->disk;
+
+	g->queue->make_request_fn		= flash_dev_make_request;
+	g->queue->backing_dev_info.congested_fn = flash_dev_congested;
+	d->cache_miss				= flash_dev_cache_miss;
+	d->ioctl				= flash_dev_ioctl;
+}
+
+void bch_request_exit(void)
+{
+#ifdef CONFIG_CGROUP_BCACHE
+	cgroup_unload_subsys(&bcache_subsys);
+#endif
+	if (bch_search_cache)
+		kmem_cache_destroy(bch_search_cache);
+}
+
+int __init bch_request_init(void)
+{
+	bch_search_cache = KMEM_CACHE(search, 0);
+	if (!bch_search_cache)
+		return -ENOMEM;
+
+#ifdef CONFIG_CGROUP_BCACHE
+	cgroup_load_subsys(&bcache_subsys);
+	init_bch_cgroup(&bcache_default_cgroup);
+
+	cgroup_add_cftypes(&bcache_subsys, bch_files);
+#endif
+	return 0;
+}