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