1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _BCACHE_BTREE_H
3 #define _BCACHE_BTREE_H
4
5 /*
6 * THE BTREE:
7 *
8 * At a high level, bcache's btree is relatively standard b+ tree. All keys and
9 * pointers are in the leaves; interior nodes only have pointers to the child
10 * nodes.
11 *
12 * In the interior nodes, a struct bkey always points to a child btree node, and
13 * the key is the highest key in the child node - except that the highest key in
14 * an interior node is always MAX_KEY. The size field refers to the size on disk
15 * of the child node - this would allow us to have variable sized btree nodes
16 * (handy for keeping the depth of the btree 1 by expanding just the root).
17 *
18 * Btree nodes are themselves log structured, but this is hidden fairly
19 * thoroughly. Btree nodes on disk will in practice have extents that overlap
20 * (because they were written at different times), but in memory we never have
21 * overlapping extents - when we read in a btree node from disk, the first thing
22 * we do is resort all the sets of keys with a mergesort, and in the same pass
23 * we check for overlapping extents and adjust them appropriately.
24 *
25 * struct btree_op is a central interface to the btree code. It's used for
26 * specifying read vs. write locking, and the embedded closure is used for
27 * waiting on IO or reserve memory.
28 *
29 * BTREE CACHE:
30 *
31 * Btree nodes are cached in memory; traversing the btree might require reading
32 * in btree nodes which is handled mostly transparently.
33 *
34 * bch_btree_node_get() looks up a btree node in the cache and reads it in from
35 * disk if necessary. This function is almost never called directly though - the
36 * btree() macro is used to get a btree node, call some function on it, and
37 * unlock the node after the function returns.
38 *
39 * The root is special cased - it's taken out of the cache's lru (thus pinning
40 * it in memory), so we can find the root of the btree by just dereferencing a
41 * pointer instead of looking it up in the cache. This makes locking a bit
42 * tricky, since the root pointer is protected by the lock in the btree node it
43 * points to - the btree_root() macro handles this.
44 *
45 * In various places we must be able to allocate memory for multiple btree nodes
46 * in order to make forward progress. To do this we use the btree cache itself
47 * as a reserve; if __get_free_pages() fails, we'll find a node in the btree
48 * cache we can reuse. We can't allow more than one thread to be doing this at a
49 * time, so there's a lock, implemented by a pointer to the btree_op closure -
50 * this allows the btree_root() macro to implicitly release this lock.
51 *
52 * BTREE IO:
53 *
54 * Btree nodes never have to be explicitly read in; bch_btree_node_get() handles
55 * this.
56 *
57 * For writing, we have two btree_write structs embeddded in struct btree - one
58 * write in flight, and one being set up, and we toggle between them.
59 *
60 * Writing is done with a single function - bch_btree_write() really serves two
61 * different purposes and should be broken up into two different functions. When
62 * passing now = false, it merely indicates that the node is now dirty - calling
63 * it ensures that the dirty keys will be written at some point in the future.
64 *
65 * When passing now = true, bch_btree_write() causes a write to happen
66 * "immediately" (if there was already a write in flight, it'll cause the write
67 * to happen as soon as the previous write completes). It returns immediately
68 * though - but it takes a refcount on the closure in struct btree_op you passed
69 * to it, so a closure_sync() later can be used to wait for the write to
70 * complete.
71 *
72 * This is handy because btree_split() and garbage collection can issue writes
73 * in parallel, reducing the amount of time they have to hold write locks.
74 *
75 * LOCKING:
76 *
77 * When traversing the btree, we may need write locks starting at some level -
78 * inserting a key into the btree will typically only require a write lock on
79 * the leaf node.
80 *
81 * This is specified with the lock field in struct btree_op; lock = 0 means we
82 * take write locks at level <= 0, i.e. only leaf nodes. bch_btree_node_get()
83 * checks this field and returns the node with the appropriate lock held.
84 *
85 * If, after traversing the btree, the insertion code discovers it has to split
86 * then it must restart from the root and take new locks - to do this it changes
87 * the lock field and returns -EINTR, which causes the btree_root() macro to
88 * loop.
89 *
90 * Handling cache misses require a different mechanism for upgrading to a write
91 * lock. We do cache lookups with only a read lock held, but if we get a cache
92 * miss and we wish to insert this data into the cache, we have to insert a
93 * placeholder key to detect races - otherwise, we could race with a write and
94 * overwrite the data that was just written to the cache with stale data from
95 * the backing device.
96 *
97 * For this we use a sequence number that write locks and unlocks increment - to
98 * insert the check key it unlocks the btree node and then takes a write lock,
99 * and fails if the sequence number doesn't match.
100 */
101
102 #include "bset.h"
103 #include "debug.h"
104
105 struct btree_write {
106 atomic_t *journal;
107
108 /* If btree_split() frees a btree node, it writes a new pointer to that
109 * btree node indicating it was freed; it takes a refcount on
110 * c->prio_blocked because we can't write the gens until the new
111 * pointer is on disk. This allows btree_write_endio() to release the
112 * refcount that btree_split() took.
113 */
114 int prio_blocked;
115 };
116
117 struct btree {
118 /* Hottest entries first */
119 struct hlist_node hash;
120
121 /* Key/pointer for this btree node */
122 BKEY_PADDED(key);
123
124 /* Single bit - set when accessed, cleared by shrinker */
125 unsigned long accessed;
126 unsigned long seq;
127 struct rw_semaphore lock;
128 struct cache_set *c;
129 struct btree *parent;
130
131 struct mutex write_lock;
132
133 unsigned long flags;
134 uint16_t written; /* would be nice to kill */
135 uint8_t level;
136
137 struct btree_keys keys;
138
139 /* For outstanding btree writes, used as a lock - protects write_idx */
140 struct closure io;
141 struct semaphore io_mutex;
142
143 struct list_head list;
144 struct delayed_work work;
145
146 struct btree_write writes[2];
147 struct bio *bio;
148 };
149
150 #define BTREE_FLAG(flag) \
151 static inline bool btree_node_ ## flag(struct btree *b) \
152 { return test_bit(BTREE_NODE_ ## flag, &b->flags); } \
153 \
154 static inline void set_btree_node_ ## flag(struct btree *b) \
155 { set_bit(BTREE_NODE_ ## flag, &b->flags); }
156
157 enum btree_flags {
158 BTREE_NODE_io_error,
159 BTREE_NODE_dirty,
160 BTREE_NODE_write_idx,
161 BTREE_NODE_journal_flush,
162 };
163
164 BTREE_FLAG(io_error);
165 BTREE_FLAG(dirty);
166 BTREE_FLAG(write_idx);
167 BTREE_FLAG(journal_flush);
168
169 static inline struct btree_write *btree_current_write(struct btree *b)
170 {
171 return b->writes + btree_node_write_idx(b);
172 }
173
174 static inline struct btree_write *btree_prev_write(struct btree *b)
175 {
176 return b->writes + (btree_node_write_idx(b) ^ 1);
177 }
178
179 static inline struct bset *btree_bset_first(struct btree *b)
180 {
181 return b->keys.set->data;
182 }
183
184 static inline struct bset *btree_bset_last(struct btree *b)
185 {
186 return bset_tree_last(&b->keys)->data;
187 }
188
189 static inline unsigned int bset_block_offset(struct btree *b, struct bset *i)
190 {
191 return bset_sector_offset(&b->keys, i) >> b->c->block_bits;
192 }
193
194 static inline void set_gc_sectors(struct cache_set *c)
195 {
196 atomic_set(&c->sectors_to_gc, c->sb.bucket_size * c->nbuckets / 16);
197 }
198
199 void bkey_put(struct cache_set *c, struct bkey *k);
200
201 /* Looping macros */
202
203 #define for_each_cached_btree(b, c, iter) \
204 for (iter = 0; \
205 iter < ARRAY_SIZE((c)->bucket_hash); \
206 iter++) \
207 hlist_for_each_entry_rcu((b), (c)->bucket_hash + iter, hash)
208
209 /* Recursing down the btree */
210
211 struct btree_op {
212 /* for waiting on btree reserve in btree_split() */
213 wait_queue_entry_t wait;
214
215 /* Btree level at which we start taking write locks */
216 short lock;
217
218 unsigned int insert_collision:1;
219 };
220
221 static inline void bch_btree_op_init(struct btree_op *op, int write_lock_level)
222 {
223 memset(op, 0, sizeof(struct btree_op));
224 init_wait(&op->wait);
225 op->lock = write_lock_level;
226 }
227
228 static inline void rw_lock(bool w, struct btree *b, int level)
229 {
230 w ? down_write_nested(&b->lock, level + 1)
231 : down_read_nested(&b->lock, level + 1);
232 if (w)
233 b->seq++;
234 }
235
236 static inline void rw_unlock(bool w, struct btree *b)
237 {
238 if (w)
239 b->seq++;
240 (w ? up_write : up_read)(&b->lock);
241 }
242
243 void bch_btree_node_read_done(struct btree *b);
244 void __bch_btree_node_write(struct btree *b, struct closure *parent);
245 void bch_btree_node_write(struct btree *b, struct closure *parent);
246
247 void bch_btree_set_root(struct btree *b);
248 struct btree *__bch_btree_node_alloc(struct cache_set *c, struct btree_op *op,
249 int level, bool wait,
250 struct btree *parent);
251 struct btree *bch_btree_node_get(struct cache_set *c, struct btree_op *op,
252 struct bkey *k, int level, bool write,
253 struct btree *parent);
254
255 int bch_btree_insert_check_key(struct btree *b, struct btree_op *op,
256 struct bkey *check_key);
257 int bch_btree_insert(struct cache_set *c, struct keylist *keys,
258 atomic_t *journal_ref, struct bkey *replace_key);
259
260 int bch_gc_thread_start(struct cache_set *c);
261 void bch_initial_gc_finish(struct cache_set *c);
262 void bch_moving_gc(struct cache_set *c);
263 int bch_btree_check(struct cache_set *c);
264 void bch_initial_mark_key(struct cache_set *c, int level, struct bkey *k);
265
266 static inline void wake_up_gc(struct cache_set *c)
267 {
268 wake_up(&c->gc_wait);
269 }
270
271 static inline void force_wake_up_gc(struct cache_set *c)
272 {
273 /*
274 * Garbage collection thread only works when sectors_to_gc < 0,
275 * calling wake_up_gc() won't start gc thread if sectors_to_gc is
276 * not a nagetive value.
277 * Therefore sectors_to_gc is set to -1 here, before waking up
278 * gc thread by calling wake_up_gc(). Then gc_should_run() will
279 * give a chance to permit gc thread to run. "Give a chance" means
280 * before going into gc_should_run(), there is still possibility
281 * that c->sectors_to_gc being set to other positive value. So
282 * this routine won't 100% make sure gc thread will be woken up
283 * to run.
284 */
285 atomic_set(&c->sectors_to_gc, -1);
286 wake_up_gc(c);
287 }
288
289 #define MAP_DONE 0
290 #define MAP_CONTINUE 1
291
292 #define MAP_ALL_NODES 0
293 #define MAP_LEAF_NODES 1
294
295 #define MAP_END_KEY 1
296
297 typedef int (btree_map_nodes_fn)(struct btree_op *b_op, struct btree *b);
298 int __bch_btree_map_nodes(struct btree_op *op, struct cache_set *c,
299 struct bkey *from, btree_map_nodes_fn *fn, int flags);
300
301 static inline int bch_btree_map_nodes(struct btree_op *op, struct cache_set *c,
302 struct bkey *from, btree_map_nodes_fn *fn)
303 {
304 return __bch_btree_map_nodes(op, c, from, fn, MAP_ALL_NODES);
305 }
306
307 static inline int bch_btree_map_leaf_nodes(struct btree_op *op,
308 struct cache_set *c,
309 struct bkey *from,
310 btree_map_nodes_fn *fn)
311 {
312 return __bch_btree_map_nodes(op, c, from, fn, MAP_LEAF_NODES);
313 }
314
315 typedef int (btree_map_keys_fn)(struct btree_op *op, struct btree *b,
316 struct bkey *k);
317 int bch_btree_map_keys(struct btree_op *op, struct cache_set *c,
318 struct bkey *from, btree_map_keys_fn *fn, int flags);
319
320 typedef bool (keybuf_pred_fn)(struct keybuf *buf, struct bkey *k);
321
322 void bch_keybuf_init(struct keybuf *buf);
323 void bch_refill_keybuf(struct cache_set *c, struct keybuf *buf,
324 struct bkey *end, keybuf_pred_fn *pred);
325 bool bch_keybuf_check_overlapping(struct keybuf *buf, struct bkey *start,
326 struct bkey *end);
327 void bch_keybuf_del(struct keybuf *buf, struct keybuf_key *w);
328 struct keybuf_key *bch_keybuf_next(struct keybuf *buf);
329 struct keybuf_key *bch_keybuf_next_rescan(struct cache_set *c,
330 struct keybuf *buf,
331 struct bkey *end,
332 keybuf_pred_fn *pred);
333 void bch_update_bucket_in_use(struct cache_set *c, struct gc_stat *stats);
334 #endif