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Diffstat (limited to 'drivers/md/bcache/btree.h')
| -rw-r--r-- | drivers/md/bcache/btree.h | 405 |
1 files changed, 405 insertions, 0 deletions
diff --git a/drivers/md/bcache/btree.h b/drivers/md/bcache/btree.h new file mode 100644 index 00000000000..af4a7092a28 --- /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 |