1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _BCACHE_JOURNAL_H
3 #define _BCACHE_JOURNAL_H
4
5 /*
6 * THE JOURNAL:
7 *
8 * The journal is treated as a circular buffer of buckets - a journal entry
9 * never spans two buckets. This means (not implemented yet) we can resize the
10 * journal at runtime, and will be needed for bcache on raw flash support.
11 *
12 * Journal entries contain a list of keys, ordered by the time they were
13 * inserted; thus journal replay just has to reinsert the keys.
14 *
15 * We also keep some things in the journal header that are logically part of the
16 * superblock - all the things that are frequently updated. This is for future
17 * bcache on raw flash support; the superblock (which will become another
18 * journal) can't be moved or wear leveled, so it contains just enough
19 * information to find the main journal, and the superblock only has to be
20 * rewritten when we want to move/wear level the main journal.
21 *
22 * Currently, we don't journal BTREE_REPLACE operations - this will hopefully be
23 * fixed eventually. This isn't a bug - BTREE_REPLACE is used for insertions
24 * from cache misses, which don't have to be journaled, and for writeback and
25 * moving gc we work around it by flushing the btree to disk before updating the
26 * gc information. But it is a potential issue with incremental garbage
27 * collection, and it's fragile.
28 *
29 * OPEN JOURNAL ENTRIES:
30 *
31 * Each journal entry contains, in the header, the sequence number of the last
32 * journal entry still open - i.e. that has keys that haven't been flushed to
33 * disk in the btree.
34 *
35 * We track this by maintaining a refcount for every open journal entry, in a
36 * fifo; each entry in the fifo corresponds to a particular journal
37 * entry/sequence number. When the refcount at the tail of the fifo goes to
38 * zero, we pop it off - thus, the size of the fifo tells us the number of open
39 * journal entries
40 *
41 * We take a refcount on a journal entry when we add some keys to a journal
42 * entry that we're going to insert (held by struct btree_op), and then when we
43 * insert those keys into the btree the btree write we're setting up takes a
44 * copy of that refcount (held by struct btree_write). That refcount is dropped
45 * when the btree write completes.
46 *
47 * A struct btree_write can only hold a refcount on a single journal entry, but
48 * might contain keys for many journal entries - we handle this by making sure
49 * it always has a refcount on the _oldest_ journal entry of all the journal
50 * entries it has keys for.
51 *
52 * JOURNAL RECLAIM:
53 *
54 * As mentioned previously, our fifo of refcounts tells us the number of open
55 * journal entries; from that and the current journal sequence number we compute
56 * last_seq - the oldest journal entry we still need. We write last_seq in each
57 * journal entry, and we also have to keep track of where it exists on disk so
58 * we don't overwrite it when we loop around the journal.
59 *
60 * To do that we track, for each journal bucket, the sequence number of the
61 * newest journal entry it contains - if we don't need that journal entry we
62 * don't need anything in that bucket anymore. From that we track the last
63 * journal bucket we still need; all this is tracked in struct journal_device
64 * and updated by journal_reclaim().
65 *
66 * JOURNAL FILLING UP:
67 *
68 * There are two ways the journal could fill up; either we could run out of
69 * space to write to, or we could have too many open journal entries and run out
70 * of room in the fifo of refcounts. Since those refcounts are decremented
71 * without any locking we can't safely resize that fifo, so we handle it the
72 * same way.
73 *
74 * If the journal fills up, we start flushing dirty btree nodes until we can
75 * allocate space for a journal write again - preferentially flushing btree
76 * nodes that are pinning the oldest journal entries first.
77 */
78
79 /*
80 * Only used for holding the journal entries we read in btree_journal_read()
81 * during cache_registration
82 */
83 struct journal_replay {
84 struct list_head list;
85 atomic_t *pin;
86 struct jset j;
87 };
88
89 /*
90 * We put two of these in struct journal; we used them for writes to the
91 * journal that are being staged or in flight.
92 */
93 struct journal_write {
94 struct jset *data;
95 #define JSET_BITS 3
96
97 struct cache_set *c;
98 struct closure_waitlist wait;
99 bool dirty;
100 bool need_write;
101 };
102
103 /* Embedded in struct cache_set */
104 struct journal {
105 spinlock_t lock;
106 spinlock_t flush_write_lock;
107 bool btree_flushing;
108 /* used when waiting because the journal was full */
109 struct closure_waitlist wait;
110 struct closure io;
111 int io_in_flight;
112 struct delayed_work work;
113
114 /* Number of blocks free in the bucket(s) we're currently writing to */
115 unsigned int blocks_free;
116 uint64_t seq;
117 DECLARE_FIFO(atomic_t, pin);
118
119 BKEY_PADDED(key);
120
121 struct journal_write w[2], *cur;
122 };
123
124 /*
125 * Embedded in struct cache. First three fields refer to the array of journal
126 * buckets, in cache_sb.
127 */
128 struct journal_device {
129 /*
130 * For each journal bucket, contains the max sequence number of the
131 * journal writes it contains - so we know when a bucket can be reused.
132 */
133 uint64_t seq[SB_JOURNAL_BUCKETS];
134
135 /* Journal bucket we're currently writing to */
136 unsigned int cur_idx;
137
138 /* Last journal bucket that still contains an open journal entry */
139 unsigned int last_idx;
140
141 /* Next journal bucket to be discarded */
142 unsigned int discard_idx;
143
144 #define DISCARD_READY 0
145 #define DISCARD_IN_FLIGHT 1
146 #define DISCARD_DONE 2
147 /* 1 - discard in flight, -1 - discard completed */
148 atomic_t discard_in_flight;
149
150 struct work_struct discard_work;
151 struct bio discard_bio;
152 struct bio_vec discard_bv;
153
154 /* Bio for journal reads/writes to this device */
155 struct bio bio;
156 struct bio_vec bv[8];
157 };
158
159 #define BTREE_FLUSH_NR 8
160
161 #define journal_pin_cmp(c, l, r) \
162 (fifo_idx(&(c)->journal.pin, (l)) > fifo_idx(&(c)->journal.pin, (r)))
163
164 #define JOURNAL_PIN 20000
165
166 #define journal_full(j) \
167 (!(j)->blocks_free || fifo_free(&(j)->pin) <= 1)
168
169 struct closure;
170 struct cache_set;
171 struct btree_op;
172 struct keylist;
173
174 atomic_t *bch_journal(struct cache_set *c,
175 struct keylist *keys,
176 struct closure *parent);
177 void bch_journal_next(struct journal *j);
178 void bch_journal_mark(struct cache_set *c, struct list_head *list);
179 void bch_journal_meta(struct cache_set *c, struct closure *cl);
180 int bch_journal_read(struct cache_set *c, struct list_head *list);
181 int bch_journal_replay(struct cache_set *c, struct list_head *list);
182
183 void bch_journal_free(struct cache_set *c);
184 int bch_journal_alloc(struct cache_set *c);
185
186 #endif /* _BCACHE_JOURNAL_H */