drivers/md/bcache/journal.h

   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 */