blob: 5c6c7a14fa0f485895f58759fd201b54c24b43b3 [file] [log] [blame]
/* SPDX-License-Identifier: GPL-2.0 */
#include <linux/kernel.h>
#include <linux/types.h>
#include "bcachefs.h"
#include "bkey.h"
#include "bkey_methods.h"
#include "btree_types.h"
#include "util.h" /* for time_stats */
#include "vstructs.h"
* 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, bkey_invalid and
* bkey_deleted().
* 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.
* 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.
* 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.
* 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.
enum bset_aux_tree_type {
#define BSET_RW_AUX_TREE_VAL (U16_MAX - 1)
static inline enum bset_aux_tree_type bset_aux_tree_type(const struct bset_tree *t)
switch (t->extra) {
* BSET_CACHELINE was originally intended to match the hardware cacheline size -
* it used to be 64, but I realized the lookup code would touch slightly less
* memory if it was 128.
* It definites the number of bytes (in struct bset) per struct bkey_float in
* the auxiliar search tree - when we're done searching the bset_float tree we
* have this many bytes left that we do a linear search over.
* Since (after level 5) every level of the bset_tree is on a new cacheline,
* we're touching one fewer cacheline in the bset tree in exchange for one more
* cacheline in the linear search - but the linear search might stop before it
* gets to the second cacheline.
#define BSET_CACHELINE 256
static inline size_t btree_keys_cachelines(const struct btree *b)
return (1U << b->byte_order) / BSET_CACHELINE;
static inline size_t btree_aux_data_bytes(const struct btree *b)
return btree_keys_cachelines(b) * 8;
static inline size_t btree_aux_data_u64s(const struct btree *b)
return btree_aux_data_bytes(b) / sizeof(u64);
#define for_each_bset(_b, _t) \
for (struct bset_tree *_t = (_b)->set; _t < (_b)->set + (_b)->nsets; _t++)
#define for_each_bset_c(_b, _t) \
for (const struct bset_tree *_t = (_b)->set; _t < (_b)->set + (_b)->nsets; _t++)
#define bset_tree_for_each_key(_b, _t, _k) \
for (_k = btree_bkey_first(_b, _t); \
_k != btree_bkey_last(_b, _t); \
_k = bkey_p_next(_k))
static inline bool bset_has_ro_aux_tree(const struct bset_tree *t)
return bset_aux_tree_type(t) == BSET_RO_AUX_TREE;
static inline bool bset_has_rw_aux_tree(struct bset_tree *t)
return bset_aux_tree_type(t) == BSET_RW_AUX_TREE;
static inline void bch2_bset_set_no_aux_tree(struct btree *b,
struct bset_tree *t)
BUG_ON(t < b->set);
for (; t < b->set + ARRAY_SIZE(b->set); t++) {
t->size = 0;
t->extra = BSET_NO_AUX_TREE_VAL;
t->aux_data_offset = U16_MAX;
static inline void btree_node_set_format(struct btree *b,
struct bkey_format f)
int len;
b->format = f;
b->nr_key_bits = bkey_format_key_bits(&f);
len = bch2_compile_bkey_format(&b->format, b->aux_data);
BUG_ON(len < 0 || len > U8_MAX);
b->unpack_fn_len = len;
bch2_bset_set_no_aux_tree(b, b->set);
static inline struct bset *bset_next_set(struct btree *b,
unsigned block_bytes)
struct bset *i = btree_bset_last(b);
return ((void *) i) + round_up(vstruct_bytes(i), block_bytes);
void bch2_btree_keys_init(struct btree *);
void bch2_bset_init_first(struct btree *, struct bset *);
void bch2_bset_init_next(struct btree *, struct btree_node_entry *);
void bch2_bset_build_aux_tree(struct btree *, struct bset_tree *, bool);
void bch2_bset_insert(struct btree *, struct btree_node_iter *,
struct bkey_packed *, struct bkey_i *, unsigned);
void bch2_bset_delete(struct btree *, struct bkey_packed *, unsigned);
/* Bkey utility code */
/* packed or unpacked */
static inline int bkey_cmp_p_or_unp(const struct btree *b,
const struct bkey_packed *l,
const struct bkey_packed *r_packed,
const struct bpos *r)
EBUG_ON(r_packed && !bkey_packed(r_packed));
if (unlikely(!bkey_packed(l)))
return bpos_cmp(packed_to_bkey_c(l)->p, *r);
if (likely(r_packed))
return __bch2_bkey_cmp_packed_format_checked(l, r_packed, b);
return __bch2_bkey_cmp_left_packed_format_checked(b, l, r);
static inline struct bset_tree *
bch2_bkey_to_bset_inlined(struct btree *b, struct bkey_packed *k)
unsigned offset = __btree_node_key_to_offset(b, k);
for_each_bset(b, t)
if (offset <= t->end_offset) {
EBUG_ON(offset < btree_bkey_first_offset(t));
return t;
struct bset_tree *bch2_bkey_to_bset(struct btree *, struct bkey_packed *);
struct bkey_packed *bch2_bkey_prev_filter(struct btree *, struct bset_tree *,
struct bkey_packed *, unsigned);
static inline struct bkey_packed *
bch2_bkey_prev_all(struct btree *b, struct bset_tree *t, struct bkey_packed *k)
return bch2_bkey_prev_filter(b, t, k, 0);
static inline struct bkey_packed *
bch2_bkey_prev(struct btree *b, struct bset_tree *t, struct bkey_packed *k)
return bch2_bkey_prev_filter(b, t, k, 1);
/* Btree key iteration */
void bch2_btree_node_iter_push(struct btree_node_iter *, struct btree *,
const struct bkey_packed *,
const struct bkey_packed *);
void bch2_btree_node_iter_init(struct btree_node_iter *, struct btree *,
struct bpos *);
void bch2_btree_node_iter_init_from_start(struct btree_node_iter *,
struct btree *);
struct bkey_packed *bch2_btree_node_iter_bset_pos(struct btree_node_iter *,
struct btree *,
struct bset_tree *);
void bch2_btree_node_iter_sort(struct btree_node_iter *, struct btree *);
void bch2_btree_node_iter_set_drop(struct btree_node_iter *,
struct btree_node_iter_set *);
void bch2_btree_node_iter_advance(struct btree_node_iter *, struct btree *);
#define btree_node_iter_for_each(_iter, _set) \
for (_set = (_iter)->data; \
_set < (_iter)->data + ARRAY_SIZE((_iter)->data) && \
(_set)->k != (_set)->end; \
static inline bool __btree_node_iter_set_end(struct btree_node_iter *iter,
unsigned i)
return iter->data[i].k == iter->data[i].end;
static inline bool bch2_btree_node_iter_end(struct btree_node_iter *iter)
return __btree_node_iter_set_end(iter, 0);
* When keys compare equal, deleted keys compare first:
* XXX: only need to compare pointers for keys that are both within a
* btree_node_iterator - we need to break ties for prev() to work correctly
static inline int bkey_iter_cmp(const struct btree *b,
const struct bkey_packed *l,
const struct bkey_packed *r)
return bch2_bkey_cmp_packed(b, l, r)
?: (int) bkey_deleted(r) - (int) bkey_deleted(l)
?: cmp_int(l, r);
static inline int btree_node_iter_cmp(const struct btree *b,
struct btree_node_iter_set l,
struct btree_node_iter_set r)
return bkey_iter_cmp(b,
__btree_node_offset_to_key(b, l.k),
__btree_node_offset_to_key(b, r.k));
/* These assume r (the search key) is not a deleted key: */
static inline int bkey_iter_pos_cmp(const struct btree *b,
const struct bkey_packed *l,
const struct bpos *r)
return bkey_cmp_left_packed(b, l, r)
?: -((int) bkey_deleted(l));
static inline int bkey_iter_cmp_p_or_unp(const struct btree *b,
const struct bkey_packed *l,
const struct bkey_packed *r_packed,
const struct bpos *r)
return bkey_cmp_p_or_unp(b, l, r_packed, r)
?: -((int) bkey_deleted(l));
static inline struct bkey_packed *
__bch2_btree_node_iter_peek_all(struct btree_node_iter *iter,
struct btree *b)
return __btree_node_offset_to_key(b, iter->data->k);
static inline struct bkey_packed *
bch2_btree_node_iter_peek_all(struct btree_node_iter *iter, struct btree *b)
return !bch2_btree_node_iter_end(iter)
? __btree_node_offset_to_key(b, iter->data->k)
static inline struct bkey_packed *
bch2_btree_node_iter_peek(struct btree_node_iter *iter, struct btree *b)
struct bkey_packed *k;
while ((k = bch2_btree_node_iter_peek_all(iter, b)) &&
bch2_btree_node_iter_advance(iter, b);
return k;
static inline struct bkey_packed *
bch2_btree_node_iter_next_all(struct btree_node_iter *iter, struct btree *b)
struct bkey_packed *ret = bch2_btree_node_iter_peek_all(iter, b);
if (ret)
bch2_btree_node_iter_advance(iter, b);
return ret;
struct bkey_packed *bch2_btree_node_iter_prev_all(struct btree_node_iter *,
struct btree *);
struct bkey_packed *bch2_btree_node_iter_prev(struct btree_node_iter *,
struct btree *);
struct bkey_s_c bch2_btree_node_iter_peek_unpack(struct btree_node_iter *,
struct btree *,
struct bkey *);
#define for_each_btree_node_key(b, k, iter) \
for (bch2_btree_node_iter_init_from_start((iter), (b)); \
(k = bch2_btree_node_iter_peek((iter), (b))); \
bch2_btree_node_iter_advance(iter, b))
#define for_each_btree_node_key_unpack(b, k, iter, unpacked) \
for (bch2_btree_node_iter_init_from_start((iter), (b)); \
(k = bch2_btree_node_iter_peek_unpack((iter), (b), (unpacked))).k;\
bch2_btree_node_iter_advance(iter, b))
/* Accounting: */
struct btree_nr_keys bch2_btree_node_count_keys(struct btree *);
static inline void btree_keys_account_key(struct btree_nr_keys *n,
unsigned bset,
struct bkey_packed *k,
int sign)
n->live_u64s += k->u64s * sign;
n->bset_u64s[bset] += k->u64s * sign;
if (bkey_packed(k))
n->packed_keys += sign;
n->unpacked_keys += sign;
static inline void btree_keys_account_val_delta(struct btree *b,
struct bkey_packed *k,
int delta)
struct bset_tree *t = bch2_bkey_to_bset(b, k);
b->nr.live_u64s += delta;
b->nr.bset_u64s[t - b->set] += delta;
#define btree_keys_account_key_add(_nr, _bset_idx, _k) \
btree_keys_account_key(_nr, _bset_idx, _k, 1)
#define btree_keys_account_key_drop(_nr, _bset_idx, _k) \
btree_keys_account_key(_nr, _bset_idx, _k, -1)
#define btree_account_key_add(_b, _k) \
btree_keys_account_key(&(_b)->nr, \
bch2_bkey_to_bset(_b, _k) - (_b)->set, _k, 1)
#define btree_account_key_drop(_b, _k) \
btree_keys_account_key(&(_b)->nr, \
bch2_bkey_to_bset(_b, _k) - (_b)->set, _k, -1)
struct bset_stats {
struct {
size_t nr, bytes;
size_t floats;
size_t failed;
void bch2_btree_keys_stats(const struct btree *, struct bset_stats *);
void bch2_bfloat_to_text(struct printbuf *, struct btree *,
struct bkey_packed *);
/* Debug stuff */
void bch2_dump_bset(struct bch_fs *, struct btree *, struct bset *, unsigned);
void bch2_dump_btree_node(struct bch_fs *, struct btree *);
void bch2_dump_btree_node_iter(struct btree *, struct btree_node_iter *);
void __bch2_verify_btree_nr_keys(struct btree *);
void bch2_btree_node_iter_verify(struct btree_node_iter *, struct btree *);
void bch2_verify_insert_pos(struct btree *, struct bkey_packed *,
struct bkey_packed *, unsigned);
static inline void __bch2_verify_btree_nr_keys(struct btree *b) {}
static inline void bch2_btree_node_iter_verify(struct btree_node_iter *iter,
struct btree *b) {}
static inline void bch2_verify_insert_pos(struct btree *b,
struct bkey_packed *where,
struct bkey_packed *insert,
unsigned clobber_u64s) {}
static inline void bch2_verify_btree_nr_keys(struct btree *b)
if (bch2_debug_check_btree_accounting)
#endif /* _BCACHEFS_BSET_H */