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>
diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c
new file mode 100644
index 0000000..ed18115
--- /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;
+}