180 lines
6.2 KiB
C
180 lines
6.2 KiB
C
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#ifndef _BCACHE_JOURNAL_H
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#define _BCACHE_JOURNAL_H
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/*
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* THE JOURNAL:
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*
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* The journal is treated as a circular buffer of buckets - a journal entry
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* never spans two buckets. This means (not implemented yet) we can resize the
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* journal at runtime, and will be needed for bcache on raw flash support.
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*
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* Journal entries contain a list of keys, ordered by the time they were
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* inserted; thus journal replay just has to reinsert the keys.
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*
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* We also keep some things in the journal header that are logically part of the
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* superblock - all the things that are frequently updated. This is for future
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* bcache on raw flash support; the superblock (which will become another
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* journal) can't be moved or wear leveled, so it contains just enough
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* information to find the main journal, and the superblock only has to be
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* rewritten when we want to move/wear level the main journal.
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*
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* Currently, we don't journal BTREE_REPLACE operations - this will hopefully be
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* fixed eventually. This isn't a bug - BTREE_REPLACE is used for insertions
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* from cache misses, which don't have to be journaled, and for writeback and
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* moving gc we work around it by flushing the btree to disk before updating the
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* gc information. But it is a potential issue with incremental garbage
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* collection, and it's fragile.
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*
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* OPEN JOURNAL ENTRIES:
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*
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* Each journal entry contains, in the header, the sequence number of the last
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* journal entry still open - i.e. that has keys that haven't been flushed to
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* disk in the btree.
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*
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* We track this by maintaining a refcount for every open journal entry, in a
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* fifo; each entry in the fifo corresponds to a particular journal
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* entry/sequence number. When the refcount at the tail of the fifo goes to
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* zero, we pop it off - thus, the size of the fifo tells us the number of open
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* journal entries
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*
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* We take a refcount on a journal entry when we add some keys to a journal
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* entry that we're going to insert (held by struct btree_op), and then when we
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* insert those keys into the btree the btree write we're setting up takes a
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* copy of that refcount (held by struct btree_write). That refcount is dropped
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* when the btree write completes.
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*
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* A struct btree_write can only hold a refcount on a single journal entry, but
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* might contain keys for many journal entries - we handle this by making sure
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* it always has a refcount on the _oldest_ journal entry of all the journal
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* entries it has keys for.
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*
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* JOURNAL RECLAIM:
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*
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* As mentioned previously, our fifo of refcounts tells us the number of open
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* journal entries; from that and the current journal sequence number we compute
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* last_seq - the oldest journal entry we still need. We write last_seq in each
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* journal entry, and we also have to keep track of where it exists on disk so
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* we don't overwrite it when we loop around the journal.
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*
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* To do that we track, for each journal bucket, the sequence number of the
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* newest journal entry it contains - if we don't need that journal entry we
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* don't need anything in that bucket anymore. From that we track the last
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* journal bucket we still need; all this is tracked in struct journal_device
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* and updated by journal_reclaim().
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*
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* JOURNAL FILLING UP:
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*
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* There are two ways the journal could fill up; either we could run out of
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* space to write to, or we could have too many open journal entries and run out
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* of room in the fifo of refcounts. Since those refcounts are decremented
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* without any locking we can't safely resize that fifo, so we handle it the
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* same way.
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*
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* If the journal fills up, we start flushing dirty btree nodes until we can
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* allocate space for a journal write again - preferentially flushing btree
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* nodes that are pinning the oldest journal entries first.
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*/
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/*
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* Only used for holding the journal entries we read in btree_journal_read()
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* during cache_registration
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*/
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struct journal_replay {
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struct list_head list;
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atomic_t *pin;
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struct jset j;
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};
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/*
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* We put two of these in struct journal; we used them for writes to the
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* journal that are being staged or in flight.
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*/
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struct journal_write {
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struct jset *data;
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#define JSET_BITS 3
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struct cache_set *c;
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struct closure_waitlist wait;
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bool dirty;
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bool need_write;
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};
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/* Embedded in struct cache_set */
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struct journal {
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spinlock_t lock;
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/* used when waiting because the journal was full */
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struct closure_waitlist wait;
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struct closure io;
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int io_in_flight;
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struct delayed_work work;
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/* Number of blocks free in the bucket(s) we're currently writing to */
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unsigned blocks_free;
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uint64_t seq;
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DECLARE_FIFO(atomic_t, pin);
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BKEY_PADDED(key);
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struct journal_write w[2], *cur;
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};
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/*
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* Embedded in struct cache. First three fields refer to the array of journal
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* buckets, in cache_sb.
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*/
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struct journal_device {
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/*
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* For each journal bucket, contains the max sequence number of the
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* journal writes it contains - so we know when a bucket can be reused.
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*/
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uint64_t seq[SB_JOURNAL_BUCKETS];
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/* Journal bucket we're currently writing to */
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unsigned cur_idx;
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/* Last journal bucket that still contains an open journal entry */
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unsigned last_idx;
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/* Next journal bucket to be discarded */
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unsigned discard_idx;
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#define DISCARD_READY 0
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#define DISCARD_IN_FLIGHT 1
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#define DISCARD_DONE 2
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/* 1 - discard in flight, -1 - discard completed */
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atomic_t discard_in_flight;
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struct work_struct discard_work;
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struct bio discard_bio;
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struct bio_vec discard_bv;
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/* Bio for journal reads/writes to this device */
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struct bio bio;
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struct bio_vec bv[8];
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};
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#define journal_pin_cmp(c, l, r) \
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(fifo_idx(&(c)->journal.pin, (l)) > fifo_idx(&(c)->journal.pin, (r)))
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#define JOURNAL_PIN 20000
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#define journal_full(j) \
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(!(j)->blocks_free || fifo_free(&(j)->pin) <= 1)
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struct closure;
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struct cache_set;
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struct btree_op;
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struct keylist;
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atomic_t *bch_journal(struct cache_set *, struct keylist *, struct closure *);
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void bch_journal_next(struct journal *);
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void bch_journal_mark(struct cache_set *, struct list_head *);
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void bch_journal_meta(struct cache_set *, struct closure *);
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int bch_journal_read(struct cache_set *, struct list_head *);
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int bch_journal_replay(struct cache_set *, struct list_head *);
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void bch_journal_free(struct cache_set *);
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int bch_journal_alloc(struct cache_set *);
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#endif /* _BCACHE_JOURNAL_H */
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