summaryrefslogtreecommitdiffstats
path: root/drivers/md/bcache/btree.h
blob: 767e755708964ce82f36dc88e28281b5c1b90177 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
#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 {
	atomic_t		*journal;

	/* If btree_split() frees a btree node, it writes a new pointer to that
	 * btree node indicating it was freed; it takes a refcount on
	 * c->prio_blocked because we can't write the gens until the new
	 * pointer is on disk. This allows btree_write_endio() to release the
	 * refcount that btree_split() took.
	 */
	int			prio_blocked;
};

struct btree {
	/* Hottest entries first */
	struct hlist_node	hash;

	/* Key/pointer for this btree node */
	BKEY_PADDED(key);

	/* Single bit - set when accessed, cleared by shrinker */
	unsigned long		accessed;
	unsigned long		seq;
	struct rw_semaphore	lock;
	struct cache_set	*c;
	struct btree		*parent;

	unsigned long		flags;
	uint16_t		written;	/* would be nice to kill */
	uint8_t			level;
	uint8_t			nsets;
	uint8_t			page_order;

	/*
	 * Set of sorted keys - the real btree node - plus a binary search tree
	 *
	 * sets[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	sets[MAX_BSETS];

	/* For outstanding btree writes, used as a lock - protects write_idx */
	struct closure_with_waitlist	io;

	struct list_head	list;
	struct delayed_work	work;

	struct btree_write	writes[2];
	struct bio		*bio;
};

#define BTREE_FLAG(flag)						\
static inline bool btree_node_ ## flag(struct btree *b)			\
{	return test_bit(BTREE_NODE_ ## flag, &b->flags); }		\
									\
static inline void set_btree_node_ ## flag(struct btree *b)		\
{	set_bit(BTREE_NODE_ ## flag, &b->flags); }			\

enum btree_flags {
	BTREE_NODE_io_error,
	BTREE_NODE_dirty,
	BTREE_NODE_write_idx,
};

BTREE_FLAG(io_error);
BTREE_FLAG(dirty);
BTREE_FLAG(write_idx);

static inline struct btree_write *btree_current_write(struct btree *b)
{
	return b->writes + btree_node_write_idx(b);
}

static inline struct btree_write *btree_prev_write(struct btree *b)
{
	return b->writes + (btree_node_write_idx(b) ^ 1);
}

static inline unsigned bset_offset(struct btree *b, struct bset *i)
{
	return (((size_t) i) - ((size_t) b->sets->data)) >> 9;
}

static inline struct bset *write_block(struct btree *b)
{
	return ((void *) b->sets[0].data) + b->written * block_bytes(b->c);
}

static inline bool bset_written(struct btree *b, struct bset_tree *t)
{
	return t->data < write_block(b);
}

static inline bool bkey_written(struct btree *b, struct bkey *k)
{
	return k < write_block(b)->start;
}

static inline void set_gc_sectors(struct cache_set *c)
{
	atomic_set(&c->sectors_to_gc, c->sb.bucket_size * c->nbuckets / 16);
}

static inline struct bkey *bch_btree_iter_init(struct btree *b,
					       struct btree_iter *iter,
					       struct bkey *search)
{
	return __bch_btree_iter_init(b, iter, search, b->sets);
}

static inline bool bch_ptr_invalid(struct btree *b, const struct bkey *k)
{
	if (b->level)
		return bch_btree_ptr_invalid(b->c, k);
	else
		return bch_extent_ptr_invalid(b->c, k);
}

void bkey_put(struct cache_set *c, struct bkey *k);

/* Looping macros */

#define for_each_cached_btree(b, c, iter)				\
	for (iter = 0;							\
	     iter < ARRAY_SIZE((c)->bucket_hash);			\
	     iter++)							\
		hlist_for_each_entry_rcu((b), (c)->bucket_hash + iter, hash)

#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));)

/* Recursing down the btree */

struct btree_op {
	/* Btree level at which we start taking write locks */
	short			lock;

	unsigned		insert_collision:1;
};

static inline void bch_btree_op_init(struct btree_op *op, int write_lock_level)
{
	memset(op, 0, sizeof(struct btree_op));
	op->lock = write_lock_level;
}

static inline void rw_lock(bool w, struct btree *b, int level)
{
	w ? down_write_nested(&b->lock, level + 1)
	  : down_read_nested(&b->lock, level + 1);
	if (w)
		b->seq++;
}

static inline void rw_unlock(bool w, struct btree *b)
{
	if (w)
		b->seq++;
	(w ? up_write : up_read)(&b->lock);
}

void bch_btree_node_read(struct btree *);
void bch_btree_node_write(struct btree *, struct closure *);

void bch_btree_set_root(struct btree *);
struct btree *bch_btree_node_alloc(struct cache_set *, int, bool);
struct btree *bch_btree_node_get(struct cache_set *, struct bkey *, int, bool);

int bch_btree_insert_check_key(struct btree *, struct btree_op *,
			       struct bkey *);
int bch_btree_insert(struct cache_set *, struct keylist *,
		     atomic_t *, struct bkey *);

int bch_gc_thread_start(struct cache_set *);
size_t bch_btree_gc_finish(struct cache_set *);
void bch_moving_gc(struct cache_set *);
int bch_btree_check(struct cache_set *);
uint8_t __bch_btree_mark_key(struct cache_set *, int, struct bkey *);

static inline void wake_up_gc(struct cache_set *c)
{
	if (c->gc_thread)
		wake_up_process(c->gc_thread);
}

#define MAP_DONE	0
#define MAP_CONTINUE	1

#define MAP_ALL_NODES	0
#define MAP_LEAF_NODES	1

#define MAP_END_KEY	1

typedef int (btree_map_nodes_fn)(struct btree_op *, struct btree *);
int __bch_btree_map_nodes(struct btree_op *, struct cache_set *,
			  struct bkey *, btree_map_nodes_fn *, int);

static inline int bch_btree_map_nodes(struct btree_op *op, struct cache_set *c,
				      struct bkey *from, btree_map_nodes_fn *fn)
{
	return __bch_btree_map_nodes(op, c, from, fn, MAP_ALL_NODES);
}

static inline int bch_btree_map_leaf_nodes(struct btree_op *op,
					   struct cache_set *c,
					   struct bkey *from,
					   btree_map_nodes_fn *fn)
{
	return __bch_btree_map_nodes(op, c, from, fn, MAP_LEAF_NODES);
}

typedef int (btree_map_keys_fn)(struct btree_op *, struct btree *,
				struct bkey *);
int bch_btree_map_keys(struct btree_op *, struct cache_set *,
		       struct bkey *, btree_map_keys_fn *, int);

typedef bool (keybuf_pred_fn)(struct keybuf *, struct bkey *);

void bch_keybuf_init(struct keybuf *);
void bch_refill_keybuf(struct cache_set *, struct keybuf *,
		       struct bkey *, keybuf_pred_fn *);
bool bch_keybuf_check_overlapping(struct keybuf *, struct bkey *,
				  struct bkey *);
void bch_keybuf_del(struct keybuf *, struct keybuf_key *);
struct keybuf_key *bch_keybuf_next(struct keybuf *);
struct keybuf_key *bch_keybuf_next_rescan(struct cache_set *, struct keybuf *,
					  struct bkey *, keybuf_pred_fn *);

#endif
OpenPOWER on IntegriCloud