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path: root/drivers/md/bcache/bset.h
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#ifndef _BCACHE_BSET_H
#define _BCACHE_BSET_H

#include <linux/bcache-kernel.h>
#include <linux/bcache.h>
#include <linux/kernel.h>
#include <linux/types.h>

#include "bkey.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, 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.
 *
 * 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_node_iter;
struct btree_node_iter_set;
struct bkey_float;

#define MAX_BSETS		3U

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		(*key_normalize)(struct btree_keys *, struct bkey *);
	bool		(*key_merge)(struct btree_keys *,
				     struct bkey *, struct bkey *);
	bool		(*key_merge_inline)(struct btree_keys *,
					    struct btree_node_iter *,
					    struct bkey *, struct bkey *);

	/*
	 * Only used for deciding whether to use bkey_start_pos(k) or just the
	 * key itself in a couple places
	 */
	bool		is_extents;
};

struct btree_keys {
	const struct btree_keys_ops	*ops;
	u8			page_order;
	u8			nsets;
	unsigned		last_set_unwritten:1;

	/*
	 * Amount of live metadata (i.e. size of node after a compaction) in
	 * units of u64s
	 */
	unsigned		nr_live_u64s;

	/*
	 * 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];
#ifdef CONFIG_BCACHE_DEBUG
	bool			*expensive_debug_checks;
#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 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, _u64s)	(sizeof(*(_i)) + (_u64s) * sizeof(u64))
#define set_bytes(_i)		__set_bytes(_i, (_i)->u64s)

#define __set_blocks(_i, _u64s, _block_bytes)				\
	DIV_ROUND_UP((size_t) __set_bytes((_i), (_u64s)), (_block_bytes))

#define set_blocks(_i, _block_bytes)					\
	__set_blocks((_i), (_i)->u64s, (_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 *);
void bch_bset_build_written_tree(struct btree_keys *);
void bch_bset_fix_invalidated_key(struct btree_keys *, struct bkey *);

void bch_bset_insert(struct btree_keys *, struct btree_node_iter *,
		     struct bkey *);

/* Bkey utility code */

struct bkey *bkey_prev(struct btree_keys *, struct bset_tree *, struct bkey *);

static inline struct bkey *bset_bkey_idx(struct bset *i, unsigned idx)
{
	return bkey_idx(i, idx);
}

/*
 * Tries to merge l and r: l should be lower than r
 * Returns true if we were able to merge. If we did merge, l will be the merged
 * key, r will be untouched.
 */
static inline bool bch_bkey_try_merge(struct btree_keys *b,
				      struct bkey *l, struct bkey *r)
{
	return b->ops->key_merge
		? b->ops->key_merge(b, l, r)
		: false;
}

static inline bool bch_bkey_try_merge_inline(struct btree_keys *b,
					     struct btree_node_iter *iter,
					     struct bkey *l, struct bkey *r)
{
	return b->ops->key_merge_inline
		? b->ops->key_merge_inline(b, iter, l, r)
		: false;
}

enum bch_extent_overlap {
	BCH_EXTENT_OVERLAP_FRONT,
	BCH_EXTENT_OVERLAP_BACK,
	BCH_EXTENT_OVERLAP_ALL,
	BCH_EXTENT_OVERLAP_MIDDLE,
};

/* Returns how k overlaps with m */
static inline enum bch_extent_overlap bch_extent_overlap(const struct bkey *k,
							 const struct bkey *m)
{
	if (bkey_cmp(k->p, m->p) < 0) {
		if (bkey_cmp(bkey_start_pos(k),
			     bkey_start_pos(m)) > 0)
			return BCH_EXTENT_OVERLAP_MIDDLE;
		else
			return BCH_EXTENT_OVERLAP_FRONT;
	} else {
		if (bkey_cmp(bkey_start_pos(k),
			     bkey_start_pos(m)) <= 0)
			return BCH_EXTENT_OVERLAP_ALL;
		else
			return BCH_EXTENT_OVERLAP_BACK;
	}
}

/* Btree key iteration */

struct btree_node_iter {
	u8		is_extents;

	unsigned	size:24;
	unsigned	used;

#ifdef CONFIG_BCACHE_DEBUG
	struct btree_keys *b;
#endif
	struct btree_node_iter_set {
		struct bkey *k, *end;
	} data[MAX_BSETS];
};

void bch_btree_node_iter_push(struct btree_node_iter *,
			      struct bkey *, struct bkey *);
void bch_btree_node_iter_init(struct btree_keys *, struct btree_node_iter *,
			      struct bpos);
void bch_btree_node_iter_init_from_start(struct btree_keys *,
					 struct btree_node_iter *);
struct bkey *bch_btree_node_iter_bset_pos(struct btree_node_iter *,
					  struct bset *);

void bch_btree_node_iter_sort(struct btree_node_iter *);
void bch_btree_node_iter_advance(struct btree_node_iter *);

static inline bool bch_btree_node_iter_end(struct btree_node_iter *iter)
{
	return !iter->used;
}

static inline struct bkey *bch_btree_node_iter_peek_all(struct btree_node_iter *iter)
{
	return bch_btree_node_iter_end(iter)
		? NULL
		: iter->data->k;
}

/* In debug mode, bch_btree_node_iter_next_all() does debug checks */

#ifdef CONFIG_BCACHE_DEBUG
struct bkey *bch_btree_node_iter_next_all(struct btree_node_iter *);
#else
static inline struct bkey *bch_btree_node_iter_next_all(struct btree_node_iter *iter)
{
	struct bkey *ret = bch_btree_node_iter_peek_all(iter);

	if (ret)
		bch_btree_node_iter_advance(iter);

	return ret;
}
#endif

static inline struct bkey *bch_btree_node_iter_next(struct btree_node_iter *iter)
{
	struct bkey *ret;

	do {
		ret = bch_btree_node_iter_next_all(iter);
	} while (ret && bkey_deleted(ret));

	return ret;
}

static inline struct bkey *bch_btree_node_iter_peek(struct btree_node_iter *iter)
{
	struct bkey *ret;

	while ((ret = bch_btree_node_iter_peek_all(iter)) &&
	       bkey_deleted(ret))
		bch_btree_node_iter_next_all(iter);

	return ret;
}

static inline struct bkey *
bch_btree_node_iter_peek_overlapping(struct btree_node_iter *iter,
				     struct bkey *end)
{
	struct bkey *ret;

	while ((ret = bch_btree_node_iter_peek_all(iter)) &&
	       (bkey_cmp(ret->p, bkey_start_pos(end)) <= 0))
		bch_btree_node_iter_next_all(iter);

	return ret && bkey_cmp(bkey_start_pos(ret), end->p) < 0 ? ret : NULL;
}

/*
 * Iterates over all _live_ keys - skipping deleted (and potentially
 * overlapping) keys
 */
#define for_each_btree_node_key(b, k, iter)				\
	for (bch_btree_node_iter_init_from_start((b), (iter));		\
	     ((k) = bch_btree_node_iter_next(iter));)

#define for_each_btree_node_key_all(b, k, iter)				\
	for (bch_btree_node_iter_init_from_start((b), (iter));		\
	     ((k) = bch_btree_node_iter_next_all(iter));)

/* Sorting */

struct bset_sort_state {
	mempool_t		*pool;

	unsigned		page_order;
	unsigned		crit_factor;

	struct time_stats	time;
};

typedef bool (*ptr_filter_fn)(struct btree_keys *, struct bkey *);

typedef void (*btree_keys_sort_fn)(struct btree_keys *, struct bset *,
				   struct btree_node_iter *iter);

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 *, ptr_filter_fn,
			 struct bset_sort_state *);
void bch_btree_sort_into(struct btree_keys *, struct btree_keys *,
			 ptr_filter_fn, struct bset_sort_state *);
void bch_btree_sort_and_fix_extents(struct btree_keys *, struct btree_node_iter *,
				    btree_keys_sort_fn, struct bset_sort_state *);
void bch_btree_sort_partial(struct btree_keys *, unsigned,
			    ptr_filter_fn, struct bset_sort_state *);

static inline void bch_btree_sort(struct btree_keys *b,
				  ptr_filter_fn filter,
				  struct bset_sort_state *state)
{
	bch_btree_sort_partial(b, 0, filter, 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 *);

size_t bch_btree_count_u64s(struct btree_keys *);

static inline void verify_nr_live_u64s(struct btree_keys *b)
{
#ifdef CONFIG_BCACHE_DEBUG
	BUG_ON(b->nr_live_u64s != bch_btree_count_u64s(b));
#endif
}

/* Debug stuff */

#ifdef CONFIG_BCACHE_DEBUG

s64 bch_count_data(struct btree_keys *);
void bch_dump_bucket(struct btree_keys *);
void bch_btree_node_iter_verify(struct btree_keys *, struct btree_node_iter *);

#else

static inline s64 bch_count_data(struct btree_keys *b) { return -1; }
static inline void bch_dump_bucket(struct btree_keys *b) {}
static inline void bch_btree_node_iter_verify(struct btree_keys *b,
					 struct btree_node_iter *iter) {}

#endif

void bch_dump_bset(struct btree_keys *, struct bset *, unsigned);

#endif