/* SPDX-License-Identifier: GPL-2.0 */ #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 btree { … }; #define BTREE_FLAG(flag) … enum btree_flags { … }; BTREE_FLAG(io_error); BTREE_FLAG(dirty); BTREE_FLAG(write_idx); BTREE_FLAG(journal_flush); static inline struct btree_write *btree_current_write(struct btree *b) { … } static inline struct btree_write *btree_prev_write(struct btree *b) { … } static inline struct bset *btree_bset_first(struct btree *b) { … } static inline struct bset *btree_bset_last(struct btree *b) { … } static inline unsigned int bset_block_offset(struct btree *b, struct bset *i) { … } static inline void set_gc_sectors(struct cache_set *c) { … } void bkey_put(struct cache_set *c, struct bkey *k); /* Looping macros */ #define for_each_cached_btree(b, c, iter) … /* Recursing down the btree */ struct btree_op { … }; struct btree_check_state; struct btree_check_info { … }; #define BCH_BTR_CHKTHREAD_MAX … struct btree_check_state { … }; static inline void bch_btree_op_init(struct btree_op *op, int write_lock_level) { … } static inline void rw_lock(bool w, struct btree *b, int level) { … } static inline void rw_unlock(bool w, struct btree *b) { … } void bch_btree_node_read_done(struct btree *b); void __bch_btree_node_write(struct btree *b, struct closure *parent); void bch_btree_node_write(struct btree *b, struct closure *parent); void bch_btree_set_root(struct btree *b); struct btree *__bch_btree_node_alloc(struct cache_set *c, struct btree_op *op, int level, bool wait, struct btree *parent); struct btree *bch_btree_node_get(struct cache_set *c, struct btree_op *op, struct bkey *k, int level, bool write, struct btree *parent); int bch_btree_insert_check_key(struct btree *b, struct btree_op *op, struct bkey *check_key); int bch_btree_insert(struct cache_set *c, struct keylist *keys, atomic_t *journal_ref, struct bkey *replace_key); int bch_gc_thread_start(struct cache_set *c); void bch_initial_gc_finish(struct cache_set *c); void bch_moving_gc(struct cache_set *c); int bch_btree_check(struct cache_set *c); void bch_initial_mark_key(struct cache_set *c, int level, struct bkey *k); void bch_cannibalize_unlock(struct cache_set *c); static inline void wake_up_gc(struct cache_set *c) { … } static inline void force_wake_up_gc(struct cache_set *c) { … } /* * 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 bcache_btree(fn, key, b, op, ...) … /** * 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 bcache_btree_root(fn, c, op, ...) … #define MAP_DONE … #define MAP_CONTINUE … #define MAP_ALL_NODES … #define MAP_LEAF_NODES … #define MAP_END_KEY … btree_map_nodes_fn; int __bch_btree_map_nodes(struct btree_op *op, struct cache_set *c, struct bkey *from, btree_map_nodes_fn *fn, int flags); static inline int bch_btree_map_nodes(struct btree_op *op, struct cache_set *c, struct bkey *from, btree_map_nodes_fn *fn) { … } static inline int bch_btree_map_leaf_nodes(struct btree_op *op, struct cache_set *c, struct bkey *from, btree_map_nodes_fn *fn) { … } btree_map_keys_fn; int bch_btree_map_keys(struct btree_op *op, struct cache_set *c, struct bkey *from, btree_map_keys_fn *fn, int flags); int bch_btree_map_keys_recurse(struct btree *b, struct btree_op *op, struct bkey *from, btree_map_keys_fn *fn, int flags); keybuf_pred_fn; void bch_keybuf_init(struct keybuf *buf); void bch_refill_keybuf(struct cache_set *c, struct keybuf *buf, struct bkey *end, keybuf_pred_fn *pred); bool bch_keybuf_check_overlapping(struct keybuf *buf, struct bkey *start, struct bkey *end); void bch_keybuf_del(struct keybuf *buf, struct keybuf_key *w); struct keybuf_key *bch_keybuf_next(struct keybuf *buf); struct keybuf_key *bch_keybuf_next_rescan(struct cache_set *c, struct keybuf *buf, struct bkey *end, keybuf_pred_fn *pred); void bch_update_bucket_in_use(struct cache_set *c, struct gc_stat *stats); #endif
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