LXR linux/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 */
  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