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/btree.h b/drivers/md/bcache/btree.h
new file mode 100644
index 0000000..af4a709
--- /dev/null
+++ b/drivers/md/bcache/btree.h
@@ -0,0 +1,405 @@
+#ifndef _BCACHE_BTREE_H
+#define _BCACHE_BTREE_H
+
+/*
+ * THE BTREE:
+ *
+ * At a high level, bcache's btree is relatively standard b+ tree. All keys and
+ * pointers are in the leaves; interior nodes only have pointers to the child
+ * nodes.
+ *
+ * In the interior nodes, a struct bkey always points to a child btree node, and
+ * the key is the highest key in the child node - except that the highest key in
+ * an interior node is always MAX_KEY. The size field refers to the size on disk
+ * of the child node - this would allow us to have variable sized btree nodes
+ * (handy for keeping the depth of the btree 1 by expanding just the root).
+ *
+ * Btree nodes are themselves log structured, but this is hidden fairly
+ * thoroughly. Btree nodes on disk will in practice have extents that overlap
+ * (because they were written at different times), but in memory we never have
+ * overlapping extents - when we read in a btree node from disk, the first thing
+ * we do is resort all the sets of keys with a mergesort, and in the same pass
+ * we check for overlapping extents and adjust them appropriately.
+ *
+ * struct btree_op is a central interface to the btree code. It's used for
+ * specifying read vs. write locking, and the embedded closure is used for
+ * waiting on IO or reserve memory.
+ *
+ * BTREE CACHE:
+ *
+ * Btree nodes are cached in memory; traversing the btree might require reading
+ * in btree nodes which is handled mostly transparently.
+ *
+ * bch_btree_node_get() looks up a btree node in the cache and reads it in from
+ * disk if necessary. This function is almost never called directly though - the
+ * btree() macro is used to get a btree node, call some function on it, and
+ * unlock the node after the function returns.
+ *
+ * The root is special cased - it's taken out of the cache's lru (thus pinning
+ * it in memory), so we can find the root of the btree by just dereferencing a
+ * pointer instead of looking it up in the cache. This makes locking a bit
+ * tricky, since the root pointer is protected by the lock in the btree node it
+ * points to - the btree_root() macro handles this.
+ *
+ * In various places we must be able to allocate memory for multiple btree nodes
+ * in order to make forward progress. To do this we use the btree cache itself
+ * as a reserve; if __get_free_pages() fails, we'll find a node in the btree
+ * cache we can reuse. We can't allow more than one thread to be doing this at a
+ * time, so there's a lock, implemented by a pointer to the btree_op closure -
+ * this allows the btree_root() macro to implicitly release this lock.
+ *
+ * BTREE IO:
+ *
+ * Btree nodes never have to be explicitly read in; bch_btree_node_get() handles
+ * this.
+ *
+ * For writing, we have two btree_write structs embeddded in struct btree - one
+ * write in flight, and one being set up, and we toggle between them.
+ *
+ * Writing is done with a single function - bch_btree_write() really serves two
+ * different purposes and should be broken up into two different functions. When
+ * passing now = false, it merely indicates that the node is now dirty - calling
+ * it ensures that the dirty keys will be written at some point in the future.
+ *
+ * When passing now = true, bch_btree_write() causes a write to happen
+ * "immediately" (if there was already a write in flight, it'll cause the write
+ * to happen as soon as the previous write completes). It returns immediately
+ * though - but it takes a refcount on the closure in struct btree_op you passed
+ * to it, so a closure_sync() later can be used to wait for the write to
+ * complete.
+ *
+ * This is handy because btree_split() and garbage collection can issue writes
+ * in parallel, reducing the amount of time they have to hold write locks.
+ *
+ * LOCKING:
+ *
+ * When traversing the btree, we may need write locks starting at some level -
+ * inserting a key into the btree will typically only require a write lock on
+ * the leaf node.
+ *
+ * This is specified with the lock field in struct btree_op; lock = 0 means we
+ * take write locks at level <= 0, i.e. only leaf nodes. bch_btree_node_get()
+ * checks this field and returns the node with the appropriate lock held.
+ *
+ * If, after traversing the btree, the insertion code discovers it has to split
+ * then it must restart from the root and take new locks - to do this it changes
+ * the lock field and returns -EINTR, which causes the btree_root() macro to
+ * loop.
+ *
+ * Handling cache misses require a different mechanism for upgrading to a write
+ * lock. We do cache lookups with only a read lock held, but if we get a cache
+ * miss and we wish to insert this data into the cache, we have to insert a
+ * placeholder key to detect races - otherwise, we could race with a write and
+ * overwrite the data that was just written to the cache with stale data from
+ * the backing device.
+ *
+ * For this we use a sequence number that write locks and unlocks increment - to
+ * insert the check key it unlocks the btree node and then takes a write lock,
+ * and fails if the sequence number doesn't match.
+ */
+
+#include "bset.h"
+#include "debug.h"
+
+struct btree_write {
+ struct closure *owner;
+ atomic_t *journal;
+
+ /* If btree_split() frees a btree node, it writes a new pointer to that
+ * btree node indicating it was freed; it takes a refcount on
+ * c->prio_blocked because we can't write the gens until the new
+ * pointer is on disk. This allows btree_write_endio() to release the
+ * refcount that btree_split() took.
+ */
+ int prio_blocked;
+};
+
+struct btree {
+ /* Hottest entries first */
+ struct hlist_node hash;
+
+ /* Key/pointer for this btree node */
+ BKEY_PADDED(key);
+
+ /* Single bit - set when accessed, cleared by shrinker */
+ unsigned long accessed;
+ unsigned long seq;
+ struct rw_semaphore lock;
+ struct cache_set *c;
+
+ unsigned long flags;
+ uint16_t written; /* would be nice to kill */
+ uint8_t level;
+ uint8_t nsets;
+ uint8_t page_order;
+
+ /*
+ * Set of sorted keys - the real btree node - plus a binary search tree
+ *
+ * sets[0] is special; set[0]->tree, set[0]->prev and set[0]->data point
+ * to the memory we have allocated for this btree node. Additionally,
+ * set[0]->data points to the entire btree node as it exists on disk.
+ */
+ struct bset_tree sets[MAX_BSETS];
+
+ /* Used to refcount bio splits, also protects b->bio */
+ struct closure_with_waitlist io;
+
+ /* Gets transferred to w->prio_blocked - see the comment there */
+ int prio_blocked;
+
+ struct list_head list;
+ struct delayed_work work;
+
+ uint64_t io_start_time;
+ struct btree_write writes[2];
+ struct bio *bio;
+};
+
+#define BTREE_FLAG(flag) \
+static inline bool btree_node_ ## flag(struct btree *b) \
+{ return test_bit(BTREE_NODE_ ## flag, &b->flags); } \
+ \
+static inline void set_btree_node_ ## flag(struct btree *b) \
+{ set_bit(BTREE_NODE_ ## flag, &b->flags); } \
+
+enum btree_flags {
+ BTREE_NODE_read_done,
+ BTREE_NODE_io_error,
+ BTREE_NODE_dirty,
+ BTREE_NODE_write_idx,
+};
+
+BTREE_FLAG(read_done);
+BTREE_FLAG(io_error);
+BTREE_FLAG(dirty);
+BTREE_FLAG(write_idx);
+
+static inline struct btree_write *btree_current_write(struct btree *b)
+{
+ return b->writes + btree_node_write_idx(b);
+}
+
+static inline struct btree_write *btree_prev_write(struct btree *b)
+{
+ return b->writes + (btree_node_write_idx(b) ^ 1);
+}
+
+static inline unsigned bset_offset(struct btree *b, struct bset *i)
+{
+ return (((size_t) i) - ((size_t) b->sets->data)) >> 9;
+}
+
+static inline struct bset *write_block(struct btree *b)
+{
+ return ((void *) b->sets[0].data) + b->written * block_bytes(b->c);
+}
+
+static inline bool bset_written(struct btree *b, struct bset_tree *t)
+{
+ return t->data < write_block(b);
+}
+
+static inline bool bkey_written(struct btree *b, struct bkey *k)
+{
+ return k < write_block(b)->start;
+}
+
+static inline void set_gc_sectors(struct cache_set *c)
+{
+ atomic_set(&c->sectors_to_gc, c->sb.bucket_size * c->nbuckets / 8);
+}
+
+static inline bool bch_ptr_invalid(struct btree *b, const struct bkey *k)
+{
+ return __bch_ptr_invalid(b->c, b->level, k);
+}
+
+static inline struct bkey *bch_btree_iter_init(struct btree *b,
+ struct btree_iter *iter,
+ struct bkey *search)
+{
+ return __bch_btree_iter_init(b, iter, search, b->sets);
+}
+
+/* Looping macros */
+
+#define for_each_cached_btree(b, c, iter) \
+ for (iter = 0; \
+ iter < ARRAY_SIZE((c)->bucket_hash); \
+ iter++) \
+ hlist_for_each_entry_rcu((b), (c)->bucket_hash + iter, hash)
+
+#define for_each_key_filter(b, k, iter, filter) \
+ for (bch_btree_iter_init((b), (iter), NULL); \
+ ((k) = bch_btree_iter_next_filter((iter), b, filter));)
+
+#define for_each_key(b, k, iter) \
+ for (bch_btree_iter_init((b), (iter), NULL); \
+ ((k) = bch_btree_iter_next(iter));)
+
+/* Recursing down the btree */
+
+struct btree_op {
+ struct closure cl;
+ struct cache_set *c;
+
+ /* Journal entry we have a refcount on */
+ atomic_t *journal;
+
+ /* Bio to be inserted into the cache */
+ struct bio *cache_bio;
+
+ unsigned inode;
+
+ uint16_t write_prio;
+
+ /* Btree level at which we start taking write locks */
+ short lock;
+
+ /* Btree insertion type */
+ enum {
+ BTREE_INSERT,
+ BTREE_REPLACE
+ } type:8;
+
+ unsigned csum:1;
+ unsigned skip:1;
+ unsigned flush_journal:1;
+
+ unsigned insert_data_done:1;
+ unsigned lookup_done:1;
+ unsigned insert_collision:1;
+
+ /* Anything after this point won't get zeroed in do_bio_hook() */
+
+ /* Keys to be inserted */
+ struct keylist keys;
+ BKEY_PADDED(replace);
+};
+
+void bch_btree_op_init_stack(struct btree_op *);
+
+static inline void rw_lock(bool w, struct btree *b, int level)
+{
+ w ? down_write_nested(&b->lock, level + 1)
+ : down_read_nested(&b->lock, level + 1);
+ if (w)
+ b->seq++;
+}
+
+static inline void rw_unlock(bool w, struct btree *b)
+{
+#ifdef CONFIG_BCACHE_EDEBUG
+ unsigned i;
+
+ if (w &&
+ b->key.ptr[0] &&
+ btree_node_read_done(b))
+ for (i = 0; i <= b->nsets; i++)
+ bch_check_key_order(b, b->sets[i].data);
+#endif
+
+ if (w)
+ b->seq++;
+ (w ? up_write : up_read)(&b->lock);
+}
+
+#define insert_lock(s, b) ((b)->level <= (s)->lock)
+
+/*
+ * These macros are for recursing down the btree - they handle the details of
+ * locking and looking up nodes in the cache for you. They're best treated as
+ * mere syntax when reading code that uses them.
+ *
+ * op->lock determines whether we take a read or a write lock at a given depth.
+ * If you've got a read lock and find that you need a write lock (i.e. you're
+ * going to have to split), set op->lock and return -EINTR; btree_root() will
+ * call you again and you'll have the correct lock.
+ */
+
+/**
+ * btree - recurse down the btree on a specified key
+ * @fn: function to call, which will be passed the child node
+ * @key: key to recurse on
+ * @b: parent btree node
+ * @op: pointer to struct btree_op
+ */
+#define btree(fn, key, b, op, ...) \
+({ \
+ int _r, l = (b)->level - 1; \
+ bool _w = l <= (op)->lock; \
+ struct btree *_b = bch_btree_node_get((b)->c, key, l, op); \
+ if (!IS_ERR(_b)) { \
+ _r = bch_btree_ ## fn(_b, op, ##__VA_ARGS__); \
+ rw_unlock(_w, _b); \
+ } else \
+ _r = PTR_ERR(_b); \
+ _r; \
+})
+
+/**
+ * btree_root - call a function on the root of the btree
+ * @fn: function to call, which will be passed the child node
+ * @c: cache set
+ * @op: pointer to struct btree_op
+ */
+#define btree_root(fn, c, op, ...) \
+({ \
+ int _r = -EINTR; \
+ do { \
+ struct btree *_b = (c)->root; \
+ bool _w = insert_lock(op, _b); \
+ rw_lock(_w, _b, _b->level); \
+ if (_b == (c)->root && \
+ _w == insert_lock(op, _b)) \
+ _r = bch_btree_ ## fn(_b, op, ##__VA_ARGS__); \
+ rw_unlock(_w, _b); \
+ bch_cannibalize_unlock(c, &(op)->cl); \
+ } while (_r == -EINTR); \
+ \
+ _r; \
+})
+
+static inline bool should_split(struct btree *b)
+{
+ struct bset *i = write_block(b);
+ return b->written >= btree_blocks(b) ||
+ (i->seq == b->sets[0].data->seq &&
+ b->written + __set_blocks(i, i->keys + 15, b->c)
+ > btree_blocks(b));
+}
+
+void bch_btree_read_done(struct closure *);
+void bch_btree_read(struct btree *);
+void bch_btree_write(struct btree *b, bool now, struct btree_op *op);
+
+void bch_cannibalize_unlock(struct cache_set *, struct closure *);
+void bch_btree_set_root(struct btree *);
+struct btree *bch_btree_node_alloc(struct cache_set *, int, struct closure *);
+struct btree *bch_btree_node_get(struct cache_set *, struct bkey *,
+ int, struct btree_op *);
+
+bool bch_btree_insert_keys(struct btree *, struct btree_op *);
+bool bch_btree_insert_check_key(struct btree *, struct btree_op *,
+ struct bio *);
+int bch_btree_insert(struct btree_op *, struct cache_set *);
+
+int bch_btree_search_recurse(struct btree *, struct btree_op *);
+
+void bch_queue_gc(struct cache_set *);
+size_t bch_btree_gc_finish(struct cache_set *);
+void bch_moving_gc(struct closure *);
+int bch_btree_check(struct cache_set *, struct btree_op *);
+uint8_t __bch_btree_mark_key(struct cache_set *, int, struct bkey *);
+
+void bch_keybuf_init(struct keybuf *, keybuf_pred_fn *);
+void bch_refill_keybuf(struct cache_set *, struct keybuf *, struct bkey *);
+bool bch_keybuf_check_overlapping(struct keybuf *, struct bkey *,
+ struct bkey *);
+void bch_keybuf_del(struct keybuf *, struct keybuf_key *);
+struct keybuf_key *bch_keybuf_next(struct keybuf *);
+struct keybuf_key *bch_keybuf_next_rescan(struct cache_set *,
+ struct keybuf *, struct bkey *);
+
+#endif