drivers/md/bcache/journal.h - maze/linux - Git at Google

 #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			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 */
	#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 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 */