- 根目录:
- drivers
- md
- bcache
- bset.h
#ifndef _BCACHE_BSET_H
#define _BCACHE_BSET_H
#include <linux/bcache.h>
#include <linux/kernel.h>
#include <linux/types.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 4U
struct bset_tree {
/*
* We construct a binary tree in an array as if the array
* started at 1, so that things line up on the same cachelines
* better: see comments in bset.c at cacheline_to_bkey() for
* details
*/
/* size of the binary tree and prev array */
unsigned size;
/* function of size - precalculated for to_inorder() */
unsigned extra;
/* copy of the last key in the set */
struct bkey end;
struct bkey_float *tree;
/*
* The nodes in the bset tree point to specific keys - this
* array holds the sizes of the previous key.
*
* Conceptually it's a member of struct bkey_float, but we want
* to keep bkey_float to 4 bytes and prev isn't used in the fast
* path.
*/
uint8_t *prev;
/* The actual btree node, with pointers to each sorted set */
struct bset *data;
};
struct btree_keys_ops {
bool (*sort_cmp)(struct btree_iter_set,
struct btree_iter_set);
struct bkey *(*sort_fixup)(struct btree_iter *, struct bkey *);
bool (*insert_fixup)(struct btree_keys *, struct bkey *,
struct btree_iter *, struct bkey *);
bool (*key_invalid)(struct btree_keys *,
const struct bkey *);
bool (*key_bad)(struct btree_keys *, const struct bkey *);
bool (*key_merge)(struct btree_keys *,
struct bkey *, struct bkey *);
void (*key_to_text)(char *, size_t, const struct bkey *);
void (*key_dump)(struct btree_keys *, const struct bkey *);
/*
* Only used for deciding whether to use START_KEY(k) or just the key
* itself in a couple places
*/
bool is_extents;
};
struct btree_keys {
const struct btree_keys_ops *ops;
uint8_t page_order;
uint8_t nsets;
unsigned last_set_unwritten:1;
bool *expensive_debug_checks;
/*
* Sets of sorted keys - the real btree node - plus a binary search tree
*
* set[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 set[MAX_BSETS];
};
static inline struct bset_tree *bset_tree_last(struct btree_keys *b)
{
return b->set + b->nsets;
}
static inline bool bset_written(struct btree_keys *b, struct bset_tree *t)
{
return t <= b->set + b->nsets - b->last_set_unwritten;
}
static inline bool bkey_written(struct btree_keys *b, struct bkey *k)
{
return !b->last_set_unwritten || k < b->set[b->nsets].data->start;
}
static inline unsigned bset_byte_offset(struct btree_keys *b, struct bset *i)
{
return ((size_t) i) - ((size_t) b->set->data);
}
static inline unsigned bset_sector_offset(struct btree_keys *b, struct bset *i)
{
return bset_byte_offset(b, i) >> 9;
}
#define __set_bytes(i, k) (sizeof(*(i)) + (k) * sizeof(uint64_t))
#define set_bytes(i) __set_bytes(i, i->keys)
#define __set_blocks(i, k, block_bytes) \
DIV_ROUND_UP(__set_bytes(i, k), block_bytes)
#define set_blocks(i, block_bytes) \
__set_blocks(i, (i)->keys, block_bytes)
static inline size_t bch_btree_keys_u64s_remaining(struct btree_keys *b)
{
struct bset_tree *t = bset_tree_last(b);
BUG_ON((PAGE_SIZE << b->page_order) <
(bset_byte_offset(b, t->data) + set_bytes(t->data)));
if (!b->last_set_unwritten)
return 0;
return ((PAGE_SIZE << b->page_order) -
(bset_byte_offset(b, t->data) + set_bytes(t->data))) /
sizeof(u64);
}
static inline struct bset *bset_next_set(struct btree_keys *b,
unsigned block_bytes)
{
struct bset *i = bset_tree_last(b)->data;
return ((void *) i) + roundup(set_bytes(i), block_bytes);
}
void bch_btree_keys_free(struct btree_keys *);
int bch_btree_keys_alloc(struct btree_keys *, unsigned, gfp_t);
void bch_btree_keys_init(struct btree_keys *, const struct btree_keys_ops *,
bool *);
void bch_bset_init_next(struct btree_keys *, struct bset *, uint64_t);
void bch_bset_build_written_tree(struct btree_keys *);
void bch_bset_fix_invalidated_key(struct btree_keys *, struct bkey *);
bool bch_bkey_try_merge(struct btree_keys *, struct bkey *, struct bkey *);
void bch_bset_insert(struct btree_keys *, struct bkey *, struct bkey *);
unsigned bch_btree_insert_key(struct btree_keys *, struct bkey *,
struct bkey *);
enum {
BTREE_INSERT_STATUS_NO_INSERT = 0,
BTREE_INSERT_STATUS_INSERT,
BTREE_INSERT_STATUS_BACK_MERGE,
BTREE_INSERT_STATUS_OVERWROTE,
BTREE_INSERT_STATUS_FRONT_MERGE,
};
/* Btree key iteration */
struct btree_iter {
size_t size, used;
#ifdef CONFIG_BCACHE_DEBUG
struct btree_keys *b;
#endif
struct btree_iter_set {
struct bkey *k, *end;
} data[MAX_BSETS];
};
typedef bool (*ptr_filter_fn)(struct btree_keys *, const struct bkey *);
struct bkey *bch_btree_iter_next(struct btree_iter *);
struct bkey *bch_btree_iter_next_filter(struct btree_iter *,
struct btree_keys *, ptr_filter_fn);
void bch_btree_iter_push(struct btree_iter *, struct bkey *, struct bkey *);
struct bkey *bch_btree_iter_init(struct btree_keys *, struct btree_iter *,
struct bkey *);
struct bkey *__bch_bset_search(struct btree_keys *, struct bset_tree *,
const struct bkey *);
/*
* 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)
{
return search ? __bch_bset_search(b, t, search) : t->data->start;
}
#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));)
/* Sorting */
struct bset_sort_state {
mempool_t *pool;
unsigned page_order;
unsigned crit_factor;
struct time_stats time;
};
void bch_bset_sort_state_free(struct bset_sort_state *);
int bch_bset_sort_state_init(struct bset_sort_state *, unsigned);
void bch_btree_sort_lazy(struct btree_keys *, struct bset_sort_state *);
void bch_btree_sort_into(struct btree_keys *, struct btree_keys *,
struct bset_sort_state *);
void bch_btree_sort_and_fix_extents(struct btree_keys *, struct btree_iter *,
struct bset_sort_state *);
void bch_btree_sort_partial(struct btree_keys *, unsigned,
struct bset_sort_state *);
static inline void bch_btree_sort(struct btree_keys *b,
struct bset_sort_state *state)
{
bch_btree_sort_partial(b, 0, state);
}
struct bset_stats {
size_t sets_written, sets_unwritten;
size_t bytes_written, bytes_unwritten;
size_t floats, failed;
};
void bch_btree_keys_stats(struct btree_keys *, struct bset_stats *);
/* Bkey utility code */
#define bset_bkey_last(i) bkey_idx((struct bkey *) (i)->d, (i)->keys)
static inline struct bkey *bset_bkey_idx(struct bset *i, unsigned idx)
{
return bkey_idx(i->start, idx);
}
static inline void bkey_init(struct bkey *k)
{
*k = ZERO_KEY;
}
static __always_inline int64_t bkey_cmp(const struct bkey *l,
const struct bkey *r)
{
return unlikely(KEY_INODE(l) != KEY_INODE(r))
? (int64_t) KEY_INODE(l) - (int64_t) KEY_INODE(r)
: (int64_t) KEY_OFFSET(l) - (int64_t) KEY_OFFSET(r);
}
void bch_bkey_copy_single_ptr(struct bkey *, const struct bkey *,
unsigned);
bool __bch_cut_front(const struct bkey *, struct bkey *);
bool __bch_cut_back(const struct bkey *, struct bkey *);
static inline bool bch_cut_front(const struct bkey *where, struct bkey *k)
{
BUG_ON(bkey_cmp(where, k) > 0);
return __bch_cut_front(where, k);
}
static inline bool bch_cut_back(const struct bkey *where, struct bkey *k)
{
BUG_ON(bkey_cmp(where, &START_KEY(k)) < 0);
return __bch_cut_back(where, k);
}
#define PRECEDING_KEY(_k) \
({ \
struct bkey *_ret = NULL; \
\
if (KEY_INODE(_k) || KEY_OFFSET(_k)) { \
_ret = &KEY(KEY_INODE(_k), KEY_OFFSET(_k), 0); \
\
if (!_ret->low) \
_ret->high--; \
_ret->low--; \
} \
\
_ret; \
})
static inline bool bch_ptr_invalid(struct btree_keys *b, const struct bkey *k)
{
return b->ops->key_invalid(b, k);
}
static inline bool bch_ptr_bad(struct btree_keys *b, const struct bkey *k)
{
return b->ops->key_bad(b, k);
}
static inline void bch_bkey_to_text(struct btree_keys *b, char *buf,
size_t size, const struct bkey *k)
{
return b->ops->key_to_text(buf, size, k);
}
static inline bool bch_bkey_equal_header(const struct bkey *l,
const struct bkey *r)
{
return (KEY_DIRTY(l) == KEY_DIRTY(r) &&
KEY_PTRS(l) == KEY_PTRS(r) &&
KEY_CSUM(l) == KEY_CSUM(r));
}
/* Keylists */
struct keylist {
union {
struct bkey *keys;
uint64_t *keys_p;
};
union {
struct bkey *top;
uint64_t *top_p;
};
/* Enough room for btree_split's keys without realloc */
#define KEYLIST_INLINE 16
uint64_t inline_keys[KEYLIST_INLINE];
};
static inline void bch_keylist_init(struct keylist *l)
{
l->top_p = l->keys_p = l->inline_keys;
}
static inline void bch_keylist_init_single(struct keylist *l, struct bkey *k)
{
l->keys = k;
l->top = bkey_next(k);
}
static inline void bch_keylist_push(struct keylist *l)
{
l->top = bkey_next(l->top);
}
static inline void bch_keylist_add(struct keylist *l, struct bkey *k)
{
bkey_copy(l->top, k);
bch_keylist_push(l);
}
static inline bool bch_keylist_empty(struct keylist *l)
{
return l->top == l->keys;
}
static inline void bch_keylist_reset(struct keylist *l)
{
l->top = l->keys;
}
static inline void bch_keylist_free(struct keylist *l)
{
if (l->keys_p != l->inline_keys)
kfree(l->keys_p);
}
static inline size_t bch_keylist_nkeys(struct keylist *l)
{
return l->top_p - l->keys_p;
}
static inline size_t bch_keylist_bytes(struct keylist *l)
{
return bch_keylist_nkeys(l) * sizeof(uint64_t);
}
struct bkey *bch_keylist_pop(struct keylist *);
void bch_keylist_pop_front(struct keylist *);
int __bch_keylist_realloc(struct keylist *, unsigned);
/* Debug stuff */
#ifdef CONFIG_BCACHE_DEBUG
int __bch_count_data(struct btree_keys *);
void __bch_check_keys(struct btree_keys *, const char *, ...);
void bch_dump_bset(struct btree_keys *, struct bset *, unsigned);
void bch_dump_bucket(struct btree_keys *);
#else
static inline int __bch_count_data(struct btree_keys *b) { return -1; }
static inline void __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 *, struct bset *, unsigned);
#endif
static inline bool btree_keys_expensive_checks(struct btree_keys *b)
{
#ifdef CONFIG_BCACHE_DEBUG
return *b->expensive_debug_checks;
#else
return false;
#endif
}
static inline int bch_count_data(struct btree_keys *b)
{
return btree_keys_expensive_checks(b) ? __bch_count_data(b) : -1;
}
#define bch_check_keys(b, ...) \
do { \
if (btree_keys_expensive_checks(b)) \
__bch_check_keys(b, __VA_ARGS__); \
} while (0)
#endif