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, 583 insertions, 0 deletions

diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c
new file mode 100644
index 00000000000..ed18115e078
--- /dev/null
+++ b/drivers/md/bcache/alloc.c
@@ -0,0 +1,583 @@
+/*
+ * Primary bucket allocation code
+ *
+ * Copyright 2012 Google, Inc.
+ *
+ * Allocation in bcache is done in terms of buckets:
+ *
+ * Each bucket has associated an 8 bit gen; this gen corresponds to the gen in
+ * btree pointers - they must match for the pointer to be considered valid.
+ *
+ * Thus (assuming a bucket has no dirty data or metadata in it) we can reuse a
+ * bucket simply by incrementing its gen.
+ *
+ * The gens (along with the priorities; it's really the gens are important but
+ * the code is named as if it's the priorities) are written in an arbitrary list
+ * of buckets on disk, with a pointer to them in the journal header.
+ *
+ * When we invalidate a bucket, we have to write its new gen to disk and wait
+ * for that write to complete before we use it - otherwise after a crash we
+ * could have pointers that appeared to be good but pointed to data that had
+ * been overwritten.
+ *
+ * Since the gens and priorities are all stored contiguously on disk, we can
+ * batch this up: We fill up the free_inc list with freshly invalidated buckets,
+ * call prio_write(), and when prio_write() finishes we pull buckets off the
+ * free_inc list and optionally discard them.
+ *
+ * free_inc isn't the only freelist - if it was, we'd often to sleep while
+ * priorities and gens were being written before we could allocate. c->free is a
+ * smaller freelist, and buckets on that list are always ready to be used.
+ *
+ * If we've got discards enabled, that happens when a bucket moves from the
+ * free_inc list to the free list.
+ *
+ * There is another freelist, because sometimes we have buckets that we know
+ * have nothing pointing into them - these we can reuse without waiting for
+ * priorities to be rewritten. These come from freed btree nodes and buckets
+ * that garbage collection discovered no longer had valid keys pointing into
+ * them (because they were overwritten). That's the unused list - buckets on the
+ * unused list move to the free list, optionally being discarded in the process.
+ *
+ * It's also important to ensure that gens don't wrap around - with respect to
+ * either the oldest gen in the btree or the gen on disk. This is quite
+ * difficult to do in practice, but we explicitly guard against it anyways - if
+ * a bucket is in danger of wrapping around we simply skip invalidating it that
+ * time around, and we garbage collect or rewrite the priorities sooner than we
+ * would have otherwise.
+ *
+ * bch_bucket_alloc() allocates a single bucket from a specific cache.
+ *
+ * bch_bucket_alloc_set() allocates one or more buckets from different caches
+ * out of a cache set.
+ *
+ * free_some_buckets() drives all the processes described above. It's called
+ * from bch_bucket_alloc() and a few other places that need to make sure free
+ * buckets are ready.
+ *
+ * invalidate_buckets_(lru|fifo)() find buckets that are available to be
+ * invalidated, and then invalidate them and stick them on the free_inc list -
+ * in either lru or fifo order.
+ */
+
+#include "bcache.h"
+#include "btree.h"
+
+#include <linux/random.h>
+
+#define MAX_IN_FLIGHT_DISCARDS		8U
+
+/* Bucket heap / gen */
+
+uint8_t bch_inc_gen(struct cache *ca, struct bucket *b)
+{
+	uint8_t ret = ++b->gen;
+
+	ca->set->need_gc = max(ca->set->need_gc, bucket_gc_gen(b));
+	WARN_ON_ONCE(ca->set->need_gc > BUCKET_GC_GEN_MAX);
+
+	if (CACHE_SYNC(&ca->set->sb)) {
+		ca->need_save_prio = max(ca->need_save_prio,
+					 bucket_disk_gen(b));
+		WARN_ON_ONCE(ca->need_save_prio > BUCKET_DISK_GEN_MAX);
+	}
+
+	return ret;
+}
+
+void bch_rescale_priorities(struct cache_set *c, int sectors)
+{
+	struct cache *ca;
+	struct bucket *b;
+	unsigned next = c->nbuckets * c->sb.bucket_size / 1024;
+	unsigned i;
+	int r;
+
+	atomic_sub(sectors, &c->rescale);
+
+	do {
+		r = atomic_read(&c->rescale);
+
+		if (r >= 0)
+			return;
+	} while (atomic_cmpxchg(&c->rescale, r, r + next) != r);
+
+	mutex_lock(&c->bucket_lock);
+
+	c->min_prio = USHRT_MAX;
+
+	for_each_cache(ca, c, i)
+		for_each_bucket(b, ca)
+			if (b->prio &&
+			    b->prio != BTREE_PRIO &&
+			    !atomic_read(&b->pin)) {
+				b->prio--;
+				c->min_prio = min(c->min_prio, b->prio);
+			}
+
+	mutex_unlock(&c->bucket_lock);
+}
+
+/* Discard/TRIM */
+
+struct discard {
+	struct list_head	list;
+	struct work_struct	work;
+	struct cache		*ca;
+	long			bucket;
+
+	struct bio		bio;
+	struct bio_vec		bv;
+};
+
+static void discard_finish(struct work_struct *w)
+{
+	struct discard *d = container_of(w, struct discard, work);
+	struct cache *ca = d->ca;
+	char buf[BDEVNAME_SIZE];
+
+	if (!test_bit(BIO_UPTODATE, &d->bio.bi_flags)) {
+		pr_notice("discard error on %s, disabling",
+			 bdevname(ca->bdev, buf));
+		d->ca->discard = 0;
+	}
+
+	mutex_lock(&ca->set->bucket_lock);
+
+	fifo_push(&ca->free, d->bucket);
+	list_add(&d->list, &ca->discards);
+	atomic_dec(&ca->discards_in_flight);
+
+	mutex_unlock(&ca->set->bucket_lock);
+
+	closure_wake_up(&ca->set->bucket_wait);
+	wake_up(&ca->set->alloc_wait);
+
+	closure_put(&ca->set->cl);
+}
+
+static void discard_endio(struct bio *bio, int error)
+{
+	struct discard *d = container_of(bio, struct discard, bio);
+	schedule_work(&d->work);
+}
+
+static void do_discard(struct cache *ca, long bucket)
+{
+	struct discard *d = list_first_entry(&ca->discards,
+					     struct discard, list);
+
+	list_del(&d->list);
+	d->bucket = bucket;
+
+	atomic_inc(&ca->discards_in_flight);
+	closure_get(&ca->set->cl);
+
+	bio_init(&d->bio);
+
+	d->bio.bi_sector	= bucket_to_sector(ca->set, d->bucket);
+	d->bio.bi_bdev		= ca->bdev;
+	d->bio.bi_rw		= REQ_WRITE|REQ_DISCARD;
+	d->bio.bi_max_vecs	= 1;
+	d->bio.bi_io_vec	= d->bio.bi_inline_vecs;
+	d->bio.bi_size		= bucket_bytes(ca);
+	d->bio.bi_end_io	= discard_endio;
+	bio_set_prio(&d->bio, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0));
+
+	submit_bio(0, &d->bio);
+}
+
+/* Allocation */
+
+static inline bool can_inc_bucket_gen(struct bucket *b)
+{
+	return bucket_gc_gen(b) < BUCKET_GC_GEN_MAX &&
+		bucket_disk_gen(b) < BUCKET_DISK_GEN_MAX;
+}
+
+bool bch_bucket_add_unused(struct cache *ca, struct bucket *b)
+{
+	BUG_ON(GC_MARK(b) || GC_SECTORS_USED(b));
+
+	if (fifo_used(&ca->free) > ca->watermark[WATERMARK_MOVINGGC] &&
+	    CACHE_REPLACEMENT(&ca->sb) == CACHE_REPLACEMENT_FIFO)
+		return false;
+
+	b->prio = 0;
+
+	if (can_inc_bucket_gen(b) &&
+	    fifo_push(&ca->unused, b - ca->buckets)) {
+		atomic_inc(&b->pin);
+		return true;
+	}
+
+	return false;
+}
+
+static bool can_invalidate_bucket(struct cache *ca, struct bucket *b)
+{
+	return GC_MARK(b) == GC_MARK_RECLAIMABLE &&
+		!atomic_read(&b->pin) &&
+		can_inc_bucket_gen(b);
+}
+
+static void invalidate_one_bucket(struct cache *ca, struct bucket *b)
+{
+	bch_inc_gen(ca, b);
+	b->prio = INITIAL_PRIO;
+	atomic_inc(&b->pin);
+	fifo_push(&ca->free_inc, b - ca->buckets);
+}
+
+static void invalidate_buckets_lru(struct cache *ca)
+{
+	unsigned bucket_prio(struct bucket *b)
+	{
+		return ((unsigned) (b->prio - ca->set->min_prio)) *
+			GC_SECTORS_USED(b);
+	}
+
+	bool bucket_max_cmp(struct bucket *l, struct bucket *r)
+	{
+		return bucket_prio(l) < bucket_prio(r);
+	}
+
+	bool bucket_min_cmp(struct bucket *l, struct bucket *r)
+	{
+		return bucket_prio(l) > bucket_prio(r);
+	}
+
+	struct bucket *b;
+	ssize_t i;
+
+	ca->heap.used = 0;
+
+	for_each_bucket(b, ca) {
+		if (!can_invalidate_bucket(ca, b))
+			continue;
+
+		if (!GC_SECTORS_USED(b)) {
+			if (!bch_bucket_add_unused(ca, b))
+				return;
+		} else {
+			if (!heap_full(&ca->heap))
+				heap_add(&ca->heap, b, bucket_max_cmp);
+			else if (bucket_max_cmp(b, heap_peek(&ca->heap))) {
+				ca->heap.data[0] = b;
+				heap_sift(&ca->heap, 0, bucket_max_cmp);
+			}
+		}
+	}
+
+	if (ca->heap.used * 2 < ca->heap.size)
+		bch_queue_gc(ca->set);
+
+	for (i = ca->heap.used / 2 - 1; i >= 0; --i)
+		heap_sift(&ca->heap, i, bucket_min_cmp);
+
+	while (!fifo_full(&ca->free_inc)) {
+		if (!heap_pop(&ca->heap, b, bucket_min_cmp)) {
+			/* We don't want to be calling invalidate_buckets()
+			 * multiple times when it can't do anything
+			 */
+			ca->invalidate_needs_gc = 1;
+			bch_queue_gc(ca->set);
+			return;
+		}
+
+		invalidate_one_bucket(ca, b);
+	}
+}
+
+static void invalidate_buckets_fifo(struct cache *ca)
+{
+	struct bucket *b;
+	size_t checked = 0;
+
+	while (!fifo_full(&ca->free_inc)) {
+		if (ca->fifo_last_bucket <  ca->sb.first_bucket ||
+		    ca->fifo_last_bucket >= ca->sb.nbuckets)
+			ca->fifo_last_bucket = ca->sb.first_bucket;
+
+		b = ca->buckets + ca->fifo_last_bucket++;
+
+		if (can_invalidate_bucket(ca, b))
+			invalidate_one_bucket(ca, b);
+
+		if (++checked >= ca->sb.nbuckets) {
+			ca->invalidate_needs_gc = 1;
+			bch_queue_gc(ca->set);
+			return;
+		}
+	}
+}
+
+static void invalidate_buckets_random(struct cache *ca)
+{
+	struct bucket *b;
+	size_t checked = 0;
+
+	while (!fifo_full(&ca->free_inc)) {
+		size_t n;
+		get_random_bytes(&n, sizeof(n));
+
+		n %= (size_t) (ca->sb.nbuckets - ca->sb.first_bucket);
+		n += ca->sb.first_bucket;
+
+		b = ca->buckets + n;
+
+		if (can_invalidate_bucket(ca, b))
+			invalidate_one_bucket(ca, b);
+
+		if (++checked >= ca->sb.nbuckets / 2) {
+			ca->invalidate_needs_gc = 1;
+			bch_queue_gc(ca->set);
+			return;
+		}
+	}
+}
+
+static void invalidate_buckets(struct cache *ca)
+{
+	if (ca->invalidate_needs_gc)
+		return;
+
+	switch (CACHE_REPLACEMENT(&ca->sb)) {
+	case CACHE_REPLACEMENT_LRU:
+		invalidate_buckets_lru(ca);
+		break;
+	case CACHE_REPLACEMENT_FIFO:
+		invalidate_buckets_fifo(ca);
+		break;
+	case CACHE_REPLACEMENT_RANDOM:
+		invalidate_buckets_random(ca);
+		break;
+	}
+}
+
+#define allocator_wait(ca, cond)					\
+do {									\
+	DEFINE_WAIT(__wait);						\
+									\
+	while (!(cond)) {						\
+		prepare_to_wait(&ca->set->alloc_wait,			\
+				&__wait, TASK_INTERRUPTIBLE);		\
+									\
+		mutex_unlock(&(ca)->set->bucket_lock);			\
+		if (test_bit(CACHE_SET_STOPPING_2, &ca->set->flags)) {	\
+			finish_wait(&ca->set->alloc_wait, &__wait);	\
+			closure_return(cl);				\
+		}							\
+									\
+		schedule();						\
+		__set_current_state(TASK_RUNNING);			\
+		mutex_lock(&(ca)->set->bucket_lock);			\
+	}								\
+									\
+	finish_wait(&ca->set->alloc_wait, &__wait);			\
+} while (0)
+
+void bch_allocator_thread(struct closure *cl)
+{
+	struct cache *ca = container_of(cl, struct cache, alloc);
+
+	mutex_lock(&ca->set->bucket_lock);
+
+	while (1) {
+		while (1) {
+			long bucket;
+
+			if ((!atomic_read(&ca->set->prio_blocked) ||
+			     !CACHE_SYNC(&ca->set->sb)) &&
+			    !fifo_empty(&ca->unused))
+				fifo_pop(&ca->unused, bucket);
+			else if (!fifo_empty(&ca->free_inc))
+				fifo_pop(&ca->free_inc, bucket);
+			else
+				break;
+
+			allocator_wait(ca, (int) fifo_free(&ca->free) >
+				       atomic_read(&ca->discards_in_flight));
+
+			if (ca->discard) {
+				allocator_wait(ca, !list_empty(&ca->discards));
+				do_discard(ca, bucket);
+			} else {
+				fifo_push(&ca->free, bucket);
+				closure_wake_up(&ca->set->bucket_wait);
+			}
+		}
+
+		allocator_wait(ca, ca->set->gc_mark_valid);
+		invalidate_buckets(ca);
+
+		allocator_wait(ca, !atomic_read(&ca->set->prio_blocked) ||
+			       !CACHE_SYNC(&ca->set->sb));
+
+		if (CACHE_SYNC(&ca->set->sb) &&
+		    (!fifo_empty(&ca->free_inc) ||
+		     ca->need_save_prio > 64)) {
+			bch_prio_write(ca);
+		}
+	}
+}
+
+long bch_bucket_alloc(struct cache *ca, unsigned watermark, struct closure *cl)
+{
+	long r = -1;
+again:
+	wake_up(&ca->set->alloc_wait);
+
+	if (fifo_used(&ca->free) > ca->watermark[watermark] &&
+	    fifo_pop(&ca->free, r)) {
+		struct bucket *b = ca->buckets + r;
+#ifdef CONFIG_BCACHE_EDEBUG
+		size_t iter;
+		long i;
+
+		for (iter = 0; iter < prio_buckets(ca) * 2; iter++)
+			BUG_ON(ca->prio_buckets[iter] == (uint64_t) r);
+
+		fifo_for_each(i, &ca->free, iter)
+			BUG_ON(i == r);
+		fifo_for_each(i, &ca->free_inc, iter)
+			BUG_ON(i == r);
+		fifo_for_each(i, &ca->unused, iter)
+			BUG_ON(i == r);
+#endif
+		BUG_ON(atomic_read(&b->pin) != 1);
+
+		SET_GC_SECTORS_USED(b, ca->sb.bucket_size);
+
+		if (watermark <= WATERMARK_METADATA) {
+			SET_GC_MARK(b, GC_MARK_METADATA);
+			b->prio = BTREE_PRIO;
+		} else {
+			SET_GC_MARK(b, GC_MARK_RECLAIMABLE);
+			b->prio = INITIAL_PRIO;
+		}
+
+		return r;
+	}
+
+	pr_debug("alloc failure: blocked %i free %zu free_inc %zu unused %zu",
+		 atomic_read(&ca->set->prio_blocked), fifo_used(&ca->free),
+		 fifo_used(&ca->free_inc), fifo_used(&ca->unused));
+
+	if (cl) {
+		closure_wait(&ca->set->bucket_wait, cl);
+
+		if (closure_blocking(cl)) {
+			mutex_unlock(&ca->set->bucket_lock);
+			closure_sync(cl);
+			mutex_lock(&ca->set->bucket_lock);
+			goto again;
+		}
+	}
+
+	return -1;
+}
+
+void bch_bucket_free(struct cache_set *c, struct bkey *k)
+{
+	unsigned i;
+
+	for (i = 0; i < KEY_PTRS(k); i++) {
+		struct bucket *b = PTR_BUCKET(c, k, i);
+
+		SET_GC_MARK(b, 0);
+		SET_GC_SECTORS_USED(b, 0);
+		bch_bucket_add_unused(PTR_CACHE(c, k, i), b);
+	}
+}
+
+int __bch_bucket_alloc_set(struct cache_set *c, unsigned watermark,
+			   struct bkey *k, int n, struct closure *cl)
+{
+	int i;
+
+	lockdep_assert_held(&c->bucket_lock);
+	BUG_ON(!n || n > c->caches_loaded || n > 8);
+
+	bkey_init(k);
+
+	/* sort by free space/prio of oldest data in caches */
+
+	for (i = 0; i < n; i++) {
+		struct cache *ca = c->cache_by_alloc[i];
+		long b = bch_bucket_alloc(ca, watermark, cl);
+
+		if (b == -1)
+			goto err;
+
+		k->ptr[i] = PTR(ca->buckets[b].gen,
+				bucket_to_sector(c, b),
+				ca->sb.nr_this_dev);
+
+		SET_KEY_PTRS(k, i + 1);
+	}
+
+	return 0;
+err:
+	bch_bucket_free(c, k);
+	__bkey_put(c, k);
+	return -1;
+}
+
+int bch_bucket_alloc_set(struct cache_set *c, unsigned watermark,
+			 struct bkey *k, int n, struct closure *cl)
+{
+	int ret;
+	mutex_lock(&c->bucket_lock);
+	ret = __bch_bucket_alloc_set(c, watermark, k, n, cl);
+	mutex_unlock(&c->bucket_lock);
+	return ret;
+}
+
+/* Init */
+
+void bch_cache_allocator_exit(struct cache *ca)
+{
+	struct discard *d;
+
+	while (!list_empty(&ca->discards)) {
+		d = list_first_entry(&ca->discards, struct discard, list);
+		cancel_work_sync(&d->work);
+		list_del(&d->list);
+		kfree(d);
+	}
+}
+
+int bch_cache_allocator_init(struct cache *ca)
+{
+	unsigned i;
+
+	/*
+	 * Reserve:
+	 * Prio/gen writes first
+	 * Then 8 for btree allocations
+	 * Then half for the moving garbage collector
+	 */
+
+	ca->watermark[WATERMARK_PRIO] = 0;
+
+	ca->watermark[WATERMARK_METADATA] = prio_buckets(ca);
+
+	ca->watermark[WATERMARK_MOVINGGC] = 8 +
+		ca->watermark[WATERMARK_METADATA];
+
+	ca->watermark[WATERMARK_NONE] = ca->free.size / 2 +
+		ca->watermark[WATERMARK_MOVINGGC];
+
+	for (i = 0; i < MAX_IN_FLIGHT_DISCARDS; i++) {
+		struct discard *d = kzalloc(sizeof(*d), GFP_KERNEL);
+		if (!d)
+			return -ENOMEM;
+
+		d->ca = ca;
+		INIT_WORK(&d->work, discard_finish);
+		list_add(&d->list, &ca->discards);
+	}
+
+	return 0;
+}