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 */ 82 struct 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 */ 92 struct journal_write { 93 struct jset *data; 94 #define JSET_BITS 3 95 96 struct cache_set *c; 97 struct closure_waitlist wait; 98 bool need_write; 99 }; 100 101 /* Embedded in struct cache_set */ 102 struct journal { 103 spinlock_t lock; 104 /* used when waiting because the journal was full */ 105 struct closure_waitlist wait; 106 struct closure io; 107 struct delayed_work work; 108 109 /* Number of blocks free in the bucket(s) we're currently writing to */ 110 unsigned blocks_free; 111 uint64_t seq; 112 DECLARE_FIFO(atomic_t, pin); 113 114 BKEY_PADDED(key); 115 116 struct journal_write w[2], *cur; 117 }; 118 119 /* 120 * Embedded in struct cache. First three fields refer to the array of journal 121 * buckets, in cache_sb. 122 */ 123 struct journal_device { 124 /* 125 * For each journal bucket, contains the max sequence number of the 126 * journal writes it contains - so we know when a bucket can be reused. 127 */ 128 uint64_t seq[SB_JOURNAL_BUCKETS]; 129 130 /* Journal bucket we're currently writing to */ 131 unsigned cur_idx; 132 133 /* Last journal bucket that still contains an open journal entry */ 134 unsigned last_idx; 135 136 /* Next journal bucket to be discarded */ 137 unsigned discard_idx; 138 139 #define DISCARD_READY 0 140 #define DISCARD_IN_FLIGHT 1 141 #define DISCARD_DONE 2 142 /* 1 - discard in flight, -1 - discard completed */ 143 atomic_t discard_in_flight; 144 145 struct work_struct discard_work; 146 struct bio discard_bio; 147 struct bio_vec discard_bv; 148 149 /* Bio for journal reads/writes to this device */ 150 struct bio bio; 151 struct bio_vec bv[8]; 152 }; 153 154 #define journal_pin_cmp(c, l, r) \ 155 (fifo_idx(&(c)->journal.pin, (l)) > fifo_idx(&(c)->journal.pin, (r))) 156 157 #define JOURNAL_PIN 20000 158 159 #define journal_full(j) \ 160 (!(j)->blocks_free || fifo_free(&(j)->pin) <= 1) 161 162 struct closure; 163 struct cache_set; 164 struct btree_op; 165 struct keylist; 166 167 atomic_t *bch_journal(struct cache_set *, struct keylist *, struct closure *); 168 void bch_journal_next(struct journal *); 169 void bch_journal_mark(struct cache_set *, struct list_head *); 170 void bch_journal_meta(struct cache_set *, struct closure *); 171 int bch_journal_read(struct cache_set *, struct list_head *); 172 int bch_journal_replay(struct cache_set *, struct list_head *); 173 174 void bch_journal_free(struct cache_set *); 175 int bch_journal_alloc(struct cache_set *); 176 177 #endif /* _BCACHE_JOURNAL_H */ 178