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Diffstat (limited to 'drivers/md/bcache/btree.h')
| -rw-r--r-- | drivers/md/bcache/btree.h | 310 |
1 files changed, 310 insertions, 0 deletions
diff --git a/drivers/md/bcache/btree.h b/drivers/md/bcache/btree.h new file mode 100644 index 000000000..5c391fa01 --- /dev/null +++ b/drivers/md/bcache/btree.h @@ -0,0 +1,310 @@ +#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 { + 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; + struct btree *parent; + + struct mutex write_lock; + + unsigned long flags; + uint16_t written; /* would be nice to kill */ + uint8_t level; + + struct btree_keys keys; + + /* For outstanding btree writes, used as a lock - protects write_idx */ + struct closure io; + struct semaphore io_mutex; + + struct list_head list; + struct delayed_work work; + + 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_io_error, + BTREE_NODE_dirty, + BTREE_NODE_write_idx, +}; + +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 struct bset *btree_bset_first(struct btree *b) +{ + return b->keys.set->data; +} + +static inline struct bset *btree_bset_last(struct btree *b) +{ + return bset_tree_last(&b->keys)->data; +} + +static inline unsigned bset_block_offset(struct btree *b, struct bset *i) +{ + return bset_sector_offset(&b->keys, i) >> b->c->block_bits; +} + +static inline void set_gc_sectors(struct cache_set *c) +{ + atomic_set(&c->sectors_to_gc, c->sb.bucket_size * c->nbuckets / 16); +} + +void bkey_put(struct cache_set *c, struct bkey *k); + +/* 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) + +/* Recursing down the btree */ + +struct btree_op { + /* for waiting on btree reserve in btree_split() */ + wait_queue_t wait; + + /* Btree level at which we start taking write locks */ + short lock; + + unsigned insert_collision:1; +}; + +static inline void bch_btree_op_init(struct btree_op *op, int write_lock_level) +{ + memset(op, 0, sizeof(struct btree_op)); + init_wait(&op->wait); + op->lock = write_lock_level; +} + +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) +{ + if (w) + b->seq++; + (w ? up_write : up_read)(&b->lock); +} + +void bch_btree_node_read_done(struct btree *); +void __bch_btree_node_write(struct btree *, struct closure *); +void bch_btree_node_write(struct btree *, struct closure *); + +void bch_btree_set_root(struct btree *); +struct btree *__bch_btree_node_alloc(struct cache_set *, struct btree_op *, + int, bool, struct btree *); +struct btree *bch_btree_node_get(struct cache_set *, struct btree_op *, + struct bkey *, int, bool, struct btree *); + +int bch_btree_insert_check_key(struct btree *, struct btree_op *, + struct bkey *); +int bch_btree_insert(struct cache_set *, struct keylist *, + atomic_t *, struct bkey *); + +int bch_gc_thread_start(struct cache_set *); +void bch_initial_gc_finish(struct cache_set *); +void bch_moving_gc(struct cache_set *); +int bch_btree_check(struct cache_set *); +void bch_initial_mark_key(struct cache_set *, int, struct bkey *); + +static inline void wake_up_gc(struct cache_set *c) +{ + if (c->gc_thread) + wake_up_process(c->gc_thread); +} + +#define MAP_DONE 0 +#define MAP_CONTINUE 1 + +#define MAP_ALL_NODES 0 +#define MAP_LEAF_NODES 1 + +#define MAP_END_KEY 1 + +typedef int (btree_map_nodes_fn)(struct btree_op *, struct btree *); +int __bch_btree_map_nodes(struct btree_op *, struct cache_set *, + struct bkey *, btree_map_nodes_fn *, int); + +static inline int bch_btree_map_nodes(struct btree_op *op, struct cache_set *c, + struct bkey *from, btree_map_nodes_fn *fn) +{ + return __bch_btree_map_nodes(op, c, from, fn, MAP_ALL_NODES); +} + +static inline int bch_btree_map_leaf_nodes(struct btree_op *op, + struct cache_set *c, + struct bkey *from, + btree_map_nodes_fn *fn) +{ + return __bch_btree_map_nodes(op, c, from, fn, MAP_LEAF_NODES); +} + +typedef int (btree_map_keys_fn)(struct btree_op *, struct btree *, + struct bkey *); +int bch_btree_map_keys(struct btree_op *, struct cache_set *, + struct bkey *, btree_map_keys_fn *, int); + +typedef bool (keybuf_pred_fn)(struct keybuf *, struct bkey *); + +void bch_keybuf_init(struct keybuf *); +void bch_refill_keybuf(struct cache_set *, struct keybuf *, + struct bkey *, keybuf_pred_fn *); +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 *, keybuf_pred_fn *); + +#endif |