/* SPDX-License-Identifier: GPL-2.0 */ #ifndef _BCACHE_BSET_H #define _BCACHE_BSET_H #include <linux/kernel.h> #include <linux/types.h> #include "bcache_ondisk.h" #include "util.h" /* for time_stats */ /* * BKEYS: * * A bkey contains a key, a size field, a variable number of pointers, and some * ancillary flag bits. * * We use two different functions for validating bkeys, bch_ptr_invalid and * bch_ptr_bad(). * * bch_ptr_invalid() primarily filters out keys and pointers that would be * invalid due to some sort of bug, whereas bch_ptr_bad() filters out keys and * pointer that occur in normal practice but don't point to real data. * * The one exception to the rule that ptr_invalid() filters out invalid keys is * that it also filters out keys of size 0 - these are keys that have been * completely overwritten. It'd be safe to delete these in memory while leaving * them on disk, just unnecessary work - so we filter them out when resorting * instead. * * We can't filter out stale keys when we're resorting, because garbage * collection needs to find them to ensure bucket gens don't wrap around - * unless we're rewriting the btree node those stale keys still exist on disk. * * We also implement functions here for removing some number of sectors from the * front or the back of a bkey - this is mainly used for fixing overlapping * extents, by removing the overlapping sectors from the older key. * * BSETS: * * A bset is an array of bkeys laid out contiguously in memory in sorted order, * along with a header. A btree node is made up of a number of these, written at * different times. * * There could be many of them on disk, but we never allow there to be more than * 4 in memory - we lazily resort as needed. * * We implement code here for creating and maintaining auxiliary search trees * (described below) for searching an individial bset, and on top of that we * implement a btree iterator. * * BTREE ITERATOR: * * Most of the code in bcache doesn't care about an individual bset - it needs * to search entire btree nodes and iterate over them in sorted order. * * The btree iterator code serves both functions; it iterates through the keys * in a btree node in sorted order, starting from either keys after a specific * point (if you pass it a search key) or the start of the btree node. * * AUXILIARY SEARCH TREES: * * Since keys are variable length, we can't use a binary search on a bset - we * wouldn't be able to find the start of the next key. But binary searches are * slow anyways, due to terrible cache behaviour; bcache originally used binary * searches and that code topped out at under 50k lookups/second. * * So we need to construct some sort of lookup table. Since we only insert keys * into the last (unwritten) set, most of the keys within a given btree node are * usually in sets that are mostly constant. We use two different types of * lookup tables to take advantage of this. * * Both lookup tables share in common that they don't index every key in the * set; they index one key every BSET_CACHELINE bytes, and then a linear search * is used for the rest. * * For sets that have been written to disk and are no longer being inserted * into, we construct a binary search tree in an array - traversing a binary * search tree in an array gives excellent locality of reference and is very * fast, since both children of any node are adjacent to each other in memory * (and their grandchildren, and great grandchildren...) - this means * prefetching can be used to great effect. * * It's quite useful performance wise to keep these nodes small - not just * because they're more likely to be in L2, but also because we can prefetch * more nodes on a single cacheline and thus prefetch more iterations in advance * when traversing this tree. * * Nodes in the auxiliary search tree must contain both a key to compare against * (we don't want to fetch the key from the set, that would defeat the purpose), * and a pointer to the key. We use a few tricks to compress both of these. * * To compress the pointer, we take advantage of the fact that one node in the * search tree corresponds to precisely BSET_CACHELINE bytes in the set. We have * a function (to_inorder()) that takes the index of a node in a binary tree and * returns what its index would be in an inorder traversal, so we only have to * store the low bits of the offset. * * The key is 84 bits (KEY_DEV + key->key, the offset on the device). To * compress that, we take advantage of the fact that when we're traversing the * search tree at every iteration we know that both our search key and the key * we're looking for lie within some range - bounded by our previous * comparisons. (We special case the start of a search so that this is true even * at the root of the tree). * * So we know the key we're looking for is between a and b, and a and b don't * differ higher than bit 50, we don't need to check anything higher than bit * 50. * * We don't usually need the rest of the bits, either; we only need enough bits * to partition the key range we're currently checking. Consider key n - the * key our auxiliary search tree node corresponds to, and key p, the key * immediately preceding n. The lowest bit we need to store in the auxiliary * search tree is the highest bit that differs between n and p. * * Note that this could be bit 0 - we might sometimes need all 80 bits to do the * comparison. But we'd really like our nodes in the auxiliary search tree to be * of fixed size. * * The solution is to make them fixed size, and when we're constructing a node * check if p and n differed in the bits we needed them to. If they don't we * flag that node, and when doing lookups we fallback to comparing against the * real key. As long as this doesn't happen to often (and it seems to reliably * happen a bit less than 1% of the time), we win - even on failures, that key * is then more likely to be in cache than if we were doing binary searches all * the way, since we're touching so much less memory. * * The keys in the auxiliary search tree are stored in (software) floating * point, with an exponent and a mantissa. The exponent needs to be big enough * to address all the bits in the original key, but the number of bits in the * mantissa is somewhat arbitrary; more bits just gets us fewer failures. * * We need 7 bits for the exponent and 3 bits for the key's offset (since keys * are 8 byte aligned); using 22 bits for the mantissa means a node is 4 bytes. * We need one node per 128 bytes in the btree node, which means the auxiliary * search trees take up 3% as much memory as the btree itself. * * Constructing these auxiliary search trees is moderately expensive, and we * don't want to be constantly rebuilding the search tree for the last set * whenever we insert another key into it. For the unwritten set, we use a much * simpler lookup table - it's just a flat array, so index i in the lookup table * corresponds to the i range of BSET_CACHELINE bytes in the set. Indexing * within each byte range works the same as with the auxiliary search trees. * * These are much easier to keep up to date when we insert a key - we do it * somewhat lazily; when we shift a key up we usually just increment the pointer * to it, only when it would overflow do we go to the trouble of finding the * first key in that range of bytes again. */ struct btree_keys; struct btree_iter; struct btree_iter_set; struct bkey_float; #define MAX_BSETS … struct bset_tree { … }; struct btree_keys_ops { … }; struct btree_keys { … }; static inline struct bset_tree *bset_tree_last(struct btree_keys *b) { … } static inline bool bset_written(struct btree_keys *b, struct bset_tree *t) { … } static inline bool bkey_written(struct btree_keys *b, struct bkey *k) { … } static inline unsigned int bset_byte_offset(struct btree_keys *b, struct bset *i) { … } static inline unsigned int bset_sector_offset(struct btree_keys *b, struct bset *i) { … } #define __set_bytes(i, k) … #define set_bytes(i) … #define __set_blocks(i, k, block_bytes) … #define set_blocks(i, block_bytes) … static inline size_t bch_btree_keys_u64s_remaining(struct btree_keys *b) { … } static inline struct bset *bset_next_set(struct btree_keys *b, unsigned int block_bytes) { … } void bch_btree_keys_free(struct btree_keys *b); int bch_btree_keys_alloc(struct btree_keys *b, unsigned int page_order, gfp_t gfp); void bch_btree_keys_init(struct btree_keys *b, const struct btree_keys_ops *ops, bool *expensive_debug_checks); void bch_bset_init_next(struct btree_keys *b, struct bset *i, uint64_t magic); void bch_bset_build_written_tree(struct btree_keys *b); void bch_bset_fix_invalidated_key(struct btree_keys *b, struct bkey *k); bool bch_bkey_try_merge(struct btree_keys *b, struct bkey *l, struct bkey *r); void bch_bset_insert(struct btree_keys *b, struct bkey *where, struct bkey *insert); unsigned int bch_btree_insert_key(struct btree_keys *b, struct bkey *k, struct bkey *replace_key); enum { … }; struct btree_iter_set { … }; /* Btree key iteration */ struct btree_iter { … }; ptr_filter_fn; struct bkey *bch_btree_iter_next(struct btree_iter *iter); struct bkey *bch_btree_iter_next_filter(struct btree_iter *iter, struct btree_keys *b, ptr_filter_fn fn); void bch_btree_iter_push(struct btree_iter *iter, struct bkey *k, struct bkey *end); struct bkey *bch_btree_iter_init(struct btree_keys *b, struct btree_iter *iter, struct bkey *search); struct bkey *__bch_bset_search(struct btree_keys *b, struct bset_tree *t, const struct bkey *search); /* * Returns the first key that is strictly greater than search */ static inline struct bkey *bch_bset_search(struct btree_keys *b, struct bset_tree *t, const struct bkey *search) { … } #define for_each_key_filter(b, k, iter, filter) … #define for_each_key(b, k, iter) … /* Sorting */ struct bset_sort_state { … }; void bch_bset_sort_state_free(struct bset_sort_state *state); int bch_bset_sort_state_init(struct bset_sort_state *state, unsigned int page_order); void bch_btree_sort_lazy(struct btree_keys *b, struct bset_sort_state *state); void bch_btree_sort_into(struct btree_keys *b, struct btree_keys *new, struct bset_sort_state *state); void bch_btree_sort_and_fix_extents(struct btree_keys *b, struct btree_iter *iter, struct bset_sort_state *state); void bch_btree_sort_partial(struct btree_keys *b, unsigned int start, struct bset_sort_state *state); static inline void bch_btree_sort(struct btree_keys *b, struct bset_sort_state *state) { … } struct bset_stats { … }; void bch_btree_keys_stats(struct btree_keys *b, struct bset_stats *state); /* Bkey utility code */ #define bset_bkey_last(i) … static inline struct bkey *bset_bkey_idx(struct bset *i, unsigned int idx) { … } static inline void bkey_init(struct bkey *k) { … } static __always_inline int64_t bkey_cmp(const struct bkey *l, const struct bkey *r) { … } void bch_bkey_copy_single_ptr(struct bkey *dest, const struct bkey *src, unsigned int i); bool __bch_cut_front(const struct bkey *where, struct bkey *k); bool __bch_cut_back(const struct bkey *where, struct bkey *k); static inline bool bch_cut_front(const struct bkey *where, struct bkey *k) { … } static inline bool bch_cut_back(const struct bkey *where, struct bkey *k) { … } /* * Pointer '*preceding_key_p' points to a memory object to store preceding * key of k. If the preceding key does not exist, set '*preceding_key_p' to * NULL. So the caller of preceding_key() needs to take care of memory * which '*preceding_key_p' pointed to before calling preceding_key(). * Currently the only caller of preceding_key() is bch_btree_insert_key(), * and it points to an on-stack variable, so the memory release is handled * by stackframe itself. */ static inline void preceding_key(struct bkey *k, struct bkey **preceding_key_p) { … } static inline bool bch_ptr_invalid(struct btree_keys *b, const struct bkey *k) { … } static inline bool bch_ptr_bad(struct btree_keys *b, const struct bkey *k) { … } static inline void bch_bkey_to_text(struct btree_keys *b, char *buf, size_t size, const struct bkey *k) { … } static inline bool bch_bkey_equal_header(const struct bkey *l, const struct bkey *r) { … } /* Keylists */ struct keylist { … }; static inline void bch_keylist_init(struct keylist *l) { … } static inline void bch_keylist_init_single(struct keylist *l, struct bkey *k) { … } static inline void bch_keylist_push(struct keylist *l) { … } static inline void bch_keylist_add(struct keylist *l, struct bkey *k) { … } static inline bool bch_keylist_empty(struct keylist *l) { … } static inline void bch_keylist_reset(struct keylist *l) { … } static inline void bch_keylist_free(struct keylist *l) { … } static inline size_t bch_keylist_nkeys(struct keylist *l) { … } static inline size_t bch_keylist_bytes(struct keylist *l) { … } struct bkey *bch_keylist_pop(struct keylist *l); void bch_keylist_pop_front(struct keylist *l); int __bch_keylist_realloc(struct keylist *l, unsigned int u64s); /* Debug stuff */ #ifdef CONFIG_BCACHE_DEBUG int __bch_count_data(struct btree_keys *b); void __printf(2, 3) __bch_check_keys(struct btree_keys *b, const char *fmt, ...); void bch_dump_bset(struct btree_keys *b, struct bset *i, unsigned int set); void bch_dump_bucket(struct btree_keys *b); #else static inline int __bch_count_data(struct btree_keys *b) { return -1; } static inline void __printf(2, 3) __bch_check_keys(struct btree_keys *b, const char *fmt, ...) {} static inline void bch_dump_bucket(struct btree_keys *b) {} void bch_dump_bset(struct btree_keys *b, struct bset *i, unsigned int set); #endif static inline bool btree_keys_expensive_checks(struct btree_keys *b) { … } static inline int bch_count_data(struct btree_keys *b) { … } #define bch_check_keys(b, ...) … #endif
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