Release 4.7 drivers/md/bcache/journal.h
#ifndef _BCACHE_JOURNAL_H
#define _BCACHE_JOURNAL_H
/*
* THE JOURNAL:
*
* The journal is treated as a circular buffer of buckets - a journal entry
* never spans two buckets. This means (not implemented yet) we can resize the
* journal at runtime, and will be needed for bcache on raw flash support.
*
* Journal entries contain a list of keys, ordered by the time they were
* inserted; thus journal replay just has to reinsert the keys.
*
* We also keep some things in the journal header that are logically part of the
* superblock - all the things that are frequently updated. This is for future
* bcache on raw flash support; the superblock (which will become another
* journal) can't be moved or wear leveled, so it contains just enough
* information to find the main journal, and the superblock only has to be
* rewritten when we want to move/wear level the main journal.
*
* Currently, we don't journal BTREE_REPLACE operations - this will hopefully be
* fixed eventually. This isn't a bug - BTREE_REPLACE is used for insertions
* from cache misses, which don't have to be journaled, and for writeback and
* moving gc we work around it by flushing the btree to disk before updating the
* gc information. But it is a potential issue with incremental garbage
* collection, and it's fragile.
*
* OPEN JOURNAL ENTRIES:
*
* Each journal entry contains, in the header, the sequence number of the last
* journal entry still open - i.e. that has keys that haven't been flushed to
* disk in the btree.
*
* We track this by maintaining a refcount for every open journal entry, in a
* fifo; each entry in the fifo corresponds to a particular journal
* entry/sequence number. When the refcount at the tail of the fifo goes to
* zero, we pop it off - thus, the size of the fifo tells us the number of open
* journal entries
*
* We take a refcount on a journal entry when we add some keys to a journal
* entry that we're going to insert (held by struct btree_op), and then when we
* insert those keys into the btree the btree write we're setting up takes a
* copy of that refcount (held by struct btree_write). That refcount is dropped
* when the btree write completes.
*
* A struct btree_write can only hold a refcount on a single journal entry, but
* might contain keys for many journal entries - we handle this by making sure
* it always has a refcount on the _oldest_ journal entry of all the journal
* entries it has keys for.
*
* JOURNAL RECLAIM:
*
* As mentioned previously, our fifo of refcounts tells us the number of open
* journal entries; from that and the current journal sequence number we compute
* last_seq - the oldest journal entry we still need. We write last_seq in each
* journal entry, and we also have to keep track of where it exists on disk so
* we don't overwrite it when we loop around the journal.
*
* To do that we track, for each journal bucket, the sequence number of the
* newest journal entry it contains - if we don't need that journal entry we
* don't need anything in that bucket anymore. From that we track the last
* journal bucket we still need; all this is tracked in struct journal_device
* and updated by journal_reclaim().
*
* JOURNAL FILLING UP:
*
* There are two ways the journal could fill up; either we could run out of
* space to write to, or we could have too many open journal entries and run out
* of room in the fifo of refcounts. Since those refcounts are decremented
* without any locking we can't safely resize that fifo, so we handle it the
* same way.
*
* If the journal fills up, we start flushing dirty btree nodes until we can
* allocate space for a journal write again - preferentially flushing btree
* nodes that are pinning the oldest journal entries first.
*/
/*
* Only used for holding the journal entries we read in btree_journal_read()
* during cache_registration
*/
struct journal_replay {
struct list_head list;
atomic_t *pin;
struct jset j;
};
/*
* We put two of these in struct journal; we used them for writes to the
* journal that are being staged or in flight.
*/
struct journal_write {
struct jset *data;
#define JSET_BITS 3
struct cache_set *c;
struct closure_waitlist wait;
bool dirty;
bool need_write;
};
/* Embedded in struct cache_set */
struct journal {
spinlock_t lock;
/* used when waiting because the journal was full */
struct closure_waitlist wait;
struct closure io;
int io_in_flight;
struct delayed_work work;
/* Number of blocks free in the bucket(s) we're currently writing to */
unsigned blocks_free;
uint64_t seq;
DECLARE_FIFO(atomic_t, pin);
BKEY_PADDED(key);
struct journal_write w[2], *cur;
};
/*
* Embedded in struct cache. First three fields refer to the array of journal
* buckets, in cache_sb.
*/
struct journal_device {
/*
* For each journal bucket, contains the max sequence number of the
* journal writes it contains - so we know when a bucket can be reused.
*/
uint64_t seq[SB_JOURNAL_BUCKETS];
/* Journal bucket we're currently writing to */
unsigned cur_idx;
/* Last journal bucket that still contains an open journal entry */
unsigned last_idx;
/* Next journal bucket to be discarded */
unsigned discard_idx;
#define DISCARD_READY 0
#define DISCARD_IN_FLIGHT 1
#define DISCARD_DONE 2
/* 1 - discard in flight, -1 - discard completed */
atomic_t discard_in_flight;
struct work_struct discard_work;
struct bio discard_bio;
struct bio_vec discard_bv;
/* Bio for journal reads/writes to this device */
struct bio bio;
struct bio_vec bv[8];
};
#define journal_pin_cmp(c, l, r) \
(fifo_idx(&(c)->journal.pin, (l)) > fifo_idx(&(c)->journal.pin, (r)))
#define JOURNAL_PIN 20000
#define journal_full(j) \
(!(j)->blocks_free || fifo_free(&(j)->pin) <= 1)
struct closure;
struct cache_set;
struct btree_op;
struct keylist;
atomic_t *bch_journal(struct cache_set *, struct keylist *, struct closure *);
void bch_journal_next(struct journal *);
void bch_journal_mark(struct cache_set *, struct list_head *);
void bch_journal_meta(struct cache_set *, struct closure *);
int bch_journal_read(struct cache_set *, struct list_head *);
int bch_journal_replay(struct cache_set *, struct list_head *);
void bch_journal_free(struct cache_set *);
int bch_journal_alloc(struct cache_set *);
#endif /* _BCACHE_JOURNAL_H */
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