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, 414 insertions, 0 deletions

diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
new file mode 100644
index 000000000000..a80ee5373fd8
--- /dev/null
+++ b/drivers/md/bcache/writeback.c
@@ -0,0 +1,414 @@
+/*
+ * background writeback - scan btree for dirty data and write it to the backing
+ * device
+ *
+ * Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
+ * Copyright 2012 Google, Inc.
+ */
+
+#include "bcache.h"
+#include "btree.h"
+#include "debug.h"
+
+static struct workqueue_struct *dirty_wq;
+
+static void read_dirty(struct closure *);
+
+struct dirty_io {
+        struct closure          cl;
+        struct cached_dev       *dc;
+        struct bio              bio;
+};
+
+/* Rate limiting */
+
+static void __update_writeback_rate(struct cached_dev *dc)
+{
+        struct cache_set *c = dc->disk.c;
+        uint64_t cache_sectors = c->nbuckets * c->sb.bucket_size;
+        uint64_t cache_dirty_target =
+                div_u64(cache_sectors * dc->writeback_percent, 100);
+
+        int64_t target = div64_u64(cache_dirty_target * bdev_sectors(dc->bdev),
+                                   c->cached_dev_sectors);
+
+        /* PD controller */
+
+        int change = 0;
+        int64_t error;
+        int64_t dirty = atomic_long_read(&dc->disk.sectors_dirty);
+        int64_t derivative = dirty - dc->disk.sectors_dirty_last;
+
+        dc->disk.sectors_dirty_last = dirty;
+
+        derivative *= dc->writeback_rate_d_term;
+        derivative = clamp(derivative, -dirty, dirty);
+
+        derivative = ewma_add(dc->disk.sectors_dirty_derivative, derivative,
+                              dc->writeback_rate_d_smooth, 0);
+
+        /* Avoid divide by zero */
+        if (!target)
+                goto out;
+
+        error = div64_s64((dirty + derivative - target) << 8, target);
+
+        change = div_s64((dc->writeback_rate.rate * error) >> 8,
+                         dc->writeback_rate_p_term_inverse);
+
+        /* Don't increase writeback rate if the device isn't keeping up */
+        if (change > 0 &&
+            time_after64(local_clock(),
+                         dc->writeback_rate.next + 10 * NSEC_PER_MSEC))
+                change = 0;
+
+        dc->writeback_rate.rate =
+                clamp_t(int64_t, dc->writeback_rate.rate + change,
+                        1, NSEC_PER_MSEC);
+out:
+        dc->writeback_rate_derivative = derivative;
+        dc->writeback_rate_change = change;
+        dc->writeback_rate_target = target;
+
+        schedule_delayed_work(&dc->writeback_rate_update,
+                              dc->writeback_rate_update_seconds * HZ);
+}
+
+static void update_writeback_rate(struct work_struct *work)
+{
+        struct cached_dev *dc = container_of(to_delayed_work(work),
+                                             struct cached_dev,
+                                             writeback_rate_update);
+
+        down_read(&dc->writeback_lock);
+
+        if (atomic_read(&dc->has_dirty) &&
+            dc->writeback_percent)
+                __update_writeback_rate(dc);
+
+        up_read(&dc->writeback_lock);
+}
+
+static unsigned writeback_delay(struct cached_dev *dc, unsigned sectors)
+{
+        if (atomic_read(&dc->disk.detaching) ||
+            !dc->writeback_percent)
+                return 0;
+
+        return next_delay(&dc->writeback_rate, sectors * 10000000ULL);
+}
+
+/* Background writeback */
+
+static bool dirty_pred(struct keybuf *buf, struct bkey *k)
+{
+        return KEY_DIRTY(k);
+}
+
+static void dirty_init(struct keybuf_key *w)
+{
+        struct dirty_io *io = w->private;
+        struct bio *bio = &io->bio;
+
+        bio_init(bio);
+        if (!io->dc->writeback_percent)
+                bio_set_prio(bio, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0));
+
+        bio->bi_size            = KEY_SIZE(&w->key) << 9;
+        bio->bi_max_vecs        = DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS);
+        bio->bi_private         = w;
+        bio->bi_io_vec          = bio->bi_inline_vecs;
+        bio_map(bio, NULL);
+}
+
+static void refill_dirty(struct closure *cl)
+{
+        struct cached_dev *dc = container_of(cl, struct cached_dev,
+                                             writeback.cl);
+        struct keybuf *buf = &dc->writeback_keys;
+        bool searched_from_start = false;
+        struct bkey end = MAX_KEY;
+        SET_KEY_INODE(&end, dc->disk.id);
+
+        if (!atomic_read(&dc->disk.detaching) &&
+            !dc->writeback_running)
+                closure_return(cl);
+
+        down_write(&dc->writeback_lock);
+
+        if (!atomic_read(&dc->has_dirty)) {
+                SET_BDEV_STATE(&dc->sb, BDEV_STATE_CLEAN);
+                bch_write_bdev_super(dc, NULL);
+
+                up_write(&dc->writeback_lock);
+                closure_return(cl);
+        }
+
+        if (bkey_cmp(&buf->last_scanned, &end) >= 0) {
+                buf->last_scanned = KEY(dc->disk.id, 0, 0);
+                searched_from_start = true;
+        }
+
+        bch_refill_keybuf(dc->disk.c, buf, &end);
+
+        if (bkey_cmp(&buf->last_scanned, &end) >= 0 && searched_from_start) {
+                /* Searched the entire btree  - delay awhile */
+
+                if (RB_EMPTY_ROOT(&buf->keys)) {
+                        atomic_set(&dc->has_dirty, 0);
+                        cached_dev_put(dc);
+                }
+
+                if (!atomic_read(&dc->disk.detaching))
+                        closure_delay(&dc->writeback, dc->writeback_delay * HZ);
+        }
+
+        up_write(&dc->writeback_lock);
+
+        ratelimit_reset(&dc->writeback_rate);
+
+        /* Punt to workqueue only so we don't recurse and blow the stack */
+        continue_at(cl, read_dirty, dirty_wq);
+}
+
+void bch_writeback_queue(struct cached_dev *dc)
+{
+        if (closure_trylock(&dc->writeback.cl, &dc->disk.cl)) {
+                if (!atomic_read(&dc->disk.detaching))
+                        closure_delay(&dc->writeback, dc->writeback_delay * HZ);
+
+                continue_at(&dc->writeback.cl, refill_dirty, dirty_wq);
+        }
+}
+
+void bch_writeback_add(struct cached_dev *dc, unsigned sectors)
+{
+        atomic_long_add(sectors, &dc->disk.sectors_dirty);
+
+        if (!atomic_read(&dc->has_dirty) &&
+            !atomic_xchg(&dc->has_dirty, 1)) {
+                atomic_inc(&dc->count);
+
+                if (BDEV_STATE(&dc->sb) != BDEV_STATE_DIRTY) {
+                        SET_BDEV_STATE(&dc->sb, BDEV_STATE_DIRTY);
+                        /* XXX: should do this synchronously */
+                        bch_write_bdev_super(dc, NULL);
+                }
+
+                bch_writeback_queue(dc);
+
+                if (dc->writeback_percent)
+                        schedule_delayed_work(&dc->writeback_rate_update,
+                                      dc->writeback_rate_update_seconds * HZ);
+        }
+}
+
+/* Background writeback - IO loop */
+
+static void dirty_io_destructor(struct closure *cl)
+{
+        struct dirty_io *io = container_of(cl, struct dirty_io, cl);
+        kfree(io);
+}
+
+static void write_dirty_finish(struct closure *cl)
+{
+        struct dirty_io *io = container_of(cl, struct dirty_io, cl);
+        struct keybuf_key *w = io->bio.bi_private;
+        struct cached_dev *dc = io->dc;
+        struct bio_vec *bv = bio_iovec_idx(&io->bio, io->bio.bi_vcnt);
+
+        while (bv-- != io->bio.bi_io_vec)
+                __free_page(bv->bv_page);
+
+        /* This is kind of a dumb way of signalling errors. */
+        if (KEY_DIRTY(&w->key)) {
+                unsigned i;
+                struct btree_op op;
+                bch_btree_op_init_stack(&op);
+
+                op.type = BTREE_REPLACE;
+                bkey_copy(&op.replace, &w->key);
+
+                SET_KEY_DIRTY(&w->key, false);
+                bch_keylist_add(&op.keys, &w->key);
+
+                for (i = 0; i < KEY_PTRS(&w->key); i++)
+                        atomic_inc(&PTR_BUCKET(dc->disk.c, &w->key, i)->pin);
+
+                pr_debug("clearing %s", pkey(&w->key));
+                bch_btree_insert(&op, dc->disk.c);
+                closure_sync(&op.cl);
+
+                atomic_long_inc(op.insert_collision
+                                ? &dc->disk.c->writeback_keys_failed
+                                : &dc->disk.c->writeback_keys_done);
+        }
+
+        bch_keybuf_del(&dc->writeback_keys, w);
+        atomic_dec_bug(&dc->in_flight);
+
+        closure_wake_up(&dc->writeback_wait);
+
+        closure_return_with_destructor(cl, dirty_io_destructor);
+}
+
+static void dirty_endio(struct bio *bio, int error)
+{
+        struct keybuf_key *w = bio->bi_private;
+        struct dirty_io *io = w->private;
+
+        if (error)
+                SET_KEY_DIRTY(&w->key, false);
+
+        closure_put(&io->cl);
+}
+
+static void write_dirty(struct closure *cl)
+{
+        struct dirty_io *io = container_of(cl, struct dirty_io, cl);
+        struct keybuf_key *w = io->bio.bi_private;
+
+        dirty_init(w);
+        io->bio.bi_rw           = WRITE;
+        io->bio.bi_sector       = KEY_START(&w->key);
+        io->bio.bi_bdev         = io->dc->bdev;
+        io->bio.bi_end_io       = dirty_endio;
+
+        trace_bcache_write_dirty(&io->bio);
+        closure_bio_submit(&io->bio, cl, &io->dc->disk);
+
+        continue_at(cl, write_dirty_finish, dirty_wq);
+}
+
+static void read_dirty_endio(struct bio *bio, int error)
+{
+        struct keybuf_key *w = bio->bi_private;
+        struct dirty_io *io = w->private;
+
+        bch_count_io_errors(PTR_CACHE(io->dc->disk.c, &w->key, 0),
+                            error, "reading dirty data from cache");
+
+        dirty_endio(bio, error);
+}
+
+static void read_dirty_submit(struct closure *cl)
+{
+        struct dirty_io *io = container_of(cl, struct dirty_io, cl);
+
+        trace_bcache_read_dirty(&io->bio);
+        closure_bio_submit(&io->bio, cl, &io->dc->disk);
+
+        continue_at(cl, write_dirty, dirty_wq);
+}
+
+static void read_dirty(struct closure *cl)
+{
+        struct cached_dev *dc = container_of(cl, struct cached_dev,
+                                             writeback.cl);
+        unsigned delay = writeback_delay(dc, 0);
+        struct keybuf_key *w;
+        struct dirty_io *io;
+
+        /*
+         * XXX: if we error, background writeback just spins. Should use some
+         * mempools.
+         */
+
+        while (1) {
+                w = bch_keybuf_next(&dc->writeback_keys);
+                if (!w)
+                        break;
+
+                BUG_ON(ptr_stale(dc->disk.c, &w->key, 0));
+
+                if (delay > 0 &&
+                    (KEY_START(&w->key) != dc->last_read ||
+                     jiffies_to_msecs(delay) > 50)) {
+                        w->private = NULL;
+
+                        closure_delay(&dc->writeback, delay);
+                        continue_at(cl, read_dirty, dirty_wq);
+                }
+
+                dc->last_read   = KEY_OFFSET(&w->key);
+
+                io = kzalloc(sizeof(struct dirty_io) + sizeof(struct bio_vec)
+                             * DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS),
+                             GFP_KERNEL);
+                if (!io)
+                        goto err;
+
+                w->private      = io;
+                io->dc          = dc;
+
+                dirty_init(w);
+                io->bio.bi_sector       = PTR_OFFSET(&w->key, 0);
+                io->bio.bi_bdev         = PTR_CACHE(dc->disk.c,
+                                                    &w->key, 0)->bdev;
+                io->bio.bi_rw           = READ;
+                io->bio.bi_end_io       = read_dirty_endio;
+
+                if (bio_alloc_pages(&io->bio, GFP_KERNEL))
+                        goto err_free;
+
+                pr_debug("%s", pkey(&w->key));
+
+                closure_call(&io->cl, read_dirty_submit, NULL, &dc->disk.cl);
+
+                delay = writeback_delay(dc, KEY_SIZE(&w->key));
+
+                atomic_inc(&dc->in_flight);
+
+                if (!closure_wait_event(&dc->writeback_wait, cl,
+                                        atomic_read(&dc->in_flight) < 64))
+                        continue_at(cl, read_dirty, dirty_wq);
+        }
+
+        if (0) {
+err_free:
+                kfree(w->private);
+err:
+                bch_keybuf_del(&dc->writeback_keys, w);
+        }
+
+        refill_dirty(cl);
+}
+
+void bch_writeback_init_cached_dev(struct cached_dev *dc)
+{
+        closure_init_unlocked(&dc->writeback);
+        init_rwsem(&dc->writeback_lock);
+
+        bch_keybuf_init(&dc->writeback_keys, dirty_pred);
+
+        dc->writeback_metadata          = true;
+        dc->writeback_running           = true;
+        dc->writeback_percent           = 10;
+        dc->writeback_delay             = 30;
+        dc->writeback_rate.rate         = 1024;
+
+        dc->writeback_rate_update_seconds = 30;
+        dc->writeback_rate_d_term       = 16;
+        dc->writeback_rate_p_term_inverse = 64;
+        dc->writeback_rate_d_smooth     = 8;
+
+        INIT_DELAYED_WORK(&dc->writeback_rate_update, update_writeback_rate);
+        schedule_delayed_work(&dc->writeback_rate_update,
+                              dc->writeback_rate_update_seconds * HZ);
+}
+
+void bch_writeback_exit(void)
+{
+        if (dirty_wq)
+                destroy_workqueue(dirty_wq);
+}
+
+int __init bch_writeback_init(void)
+{
+        dirty_wq = create_singlethread_workqueue("bcache_writeback");
+        if (!dirty_wq)
+                return -ENOMEM;
+
+        return 0;
+}