blob: f4dcca4493913fa91a36560aa4fb9aa21e4d9f86 [file] [log] [blame]
/* SPDX-License-Identifier: GPL-2.0 */
* At a high level, bcache's btree is relatively standard b+ tree. All keys and
* pointers are in the leaves; interior nodes only have pointers to the child
* nodes.
* In the interior nodes, a struct bkey always points to a child btree node, and
* the key is the highest key in the child node - except that the highest key in
* an interior node is always MAX_KEY. The size field refers to the size on disk
* of the child node - this would allow us to have variable sized btree nodes
* (handy for keeping the depth of the btree 1 by expanding just the root).
* Btree nodes are themselves log structured, but this is hidden fairly
* thoroughly. Btree nodes on disk will in practice have extents that overlap
* (because they were written at different times), but in memory we never have
* overlapping extents - when we read in a btree node from disk, the first thing
* we do is resort all the sets of keys with a mergesort, and in the same pass
* we check for overlapping extents and adjust them appropriately.
* struct btree_op is a central interface to the btree code. It's used for
* specifying read vs. write locking, and the embedded closure is used for
* waiting on IO or reserve memory.
* Btree nodes are cached in memory; traversing the btree might require reading
* in btree nodes which is handled mostly transparently.
* bch_btree_node_get() looks up a btree node in the cache and reads it in from
* disk if necessary. This function is almost never called directly though - the
* btree() macro is used to get a btree node, call some function on it, and
* unlock the node after the function returns.
* The root is special cased - it's taken out of the cache's lru (thus pinning
* it in memory), so we can find the root of the btree by just dereferencing a
* pointer instead of looking it up in the cache. This makes locking a bit
* tricky, since the root pointer is protected by the lock in the btree node it
* points to - the btree_root() macro handles this.
* In various places we must be able to allocate memory for multiple btree nodes
* in order to make forward progress. To do this we use the btree cache itself
* as a reserve; if __get_free_pages() fails, we'll find a node in the btree
* cache we can reuse. We can't allow more than one thread to be doing this at a
* time, so there's a lock, implemented by a pointer to the btree_op closure -
* this allows the btree_root() macro to implicitly release this lock.
* Btree nodes never have to be explicitly read in; bch_btree_node_get() handles
* this.
* For writing, we have two btree_write structs embeddded in struct btree - one
* write in flight, and one being set up, and we toggle between them.
* Writing is done with a single function - bch_btree_write() really serves two
* different purposes and should be broken up into two different functions. When
* passing now = false, it merely indicates that the node is now dirty - calling
* it ensures that the dirty keys will be written at some point in the future.
* When passing now = true, bch_btree_write() causes a write to happen
* "immediately" (if there was already a write in flight, it'll cause the write
* to happen as soon as the previous write completes). It returns immediately
* though - but it takes a refcount on the closure in struct btree_op you passed
* to it, so a closure_sync() later can be used to wait for the write to
* complete.
* This is handy because btree_split() and garbage collection can issue writes
* in parallel, reducing the amount of time they have to hold write locks.
* When traversing the btree, we may need write locks starting at some level -
* inserting a key into the btree will typically only require a write lock on
* the leaf node.
* This is specified with the lock field in struct btree_op; lock = 0 means we
* take write locks at level <= 0, i.e. only leaf nodes. bch_btree_node_get()
* checks this field and returns the node with the appropriate lock held.
* If, after traversing the btree, the insertion code discovers it has to split
* then it must restart from the root and take new locks - to do this it changes
* the lock field and returns -EINTR, which causes the btree_root() macro to
* loop.
* Handling cache misses require a different mechanism for upgrading to a write
* lock. We do cache lookups with only a read lock held, but if we get a cache
* miss and we wish to insert this data into the cache, we have to insert a
* placeholder key to detect races - otherwise, we could race with a write and
* overwrite the data that was just written to the cache with stale data from
* the backing device.
* For this we use a sequence number that write locks and unlocks increment - to
* insert the check key it unlocks the btree node and then takes a write lock,
* and fails if the sequence number doesn't match.
#include "bset.h"
#include "debug.h"
struct btree_write {
atomic_t *journal;
/* If btree_split() frees a btree node, it writes a new pointer to that
* btree node indicating it was freed; it takes a refcount on
* c->prio_blocked because we can't write the gens until the new
* pointer is on disk. This allows btree_write_endio() to release the
* refcount that btree_split() took.
int prio_blocked;
struct btree {
/* Hottest entries first */
struct hlist_node hash;
/* Key/pointer for this btree node */
unsigned long seq;
struct rw_semaphore lock;
struct cache_set *c;
struct btree *parent;
struct mutex write_lock;
unsigned long flags;
uint16_t written; /* would be nice to kill */
uint8_t level;
struct btree_keys keys;
/* For outstanding btree writes, used as a lock - protects write_idx */
struct closure io;
struct semaphore io_mutex;
struct list_head list;
struct delayed_work work;
struct btree_write writes[2];
struct bio *bio;
#define BTREE_FLAG(flag) \
static inline bool btree_node_ ## flag(struct btree *b) \
{ return test_bit(BTREE_NODE_ ## flag, &b->flags); } \
static inline void set_btree_node_ ## flag(struct btree *b) \
{ set_bit(BTREE_NODE_ ## flag, &b->flags); }
enum btree_flags {
static inline struct btree_write *btree_current_write(struct btree *b)
return b->writes + btree_node_write_idx(b);
static inline struct btree_write *btree_prev_write(struct btree *b)
return b->writes + (btree_node_write_idx(b) ^ 1);
static inline struct bset *btree_bset_first(struct btree *b)
return b->keys.set->data;
static inline struct bset *btree_bset_last(struct btree *b)
return bset_tree_last(&b->keys)->data;
static inline unsigned int bset_block_offset(struct btree *b, struct bset *i)
return bset_sector_offset(&b->keys, i) >> b->c->block_bits;
static inline void set_gc_sectors(struct cache_set *c)
atomic_set(&c->sectors_to_gc, c->sb.bucket_size * c->nbuckets / 16);
void bkey_put(struct cache_set *c, struct bkey *k);
/* Looping macros */
#define for_each_cached_btree(b, c, iter) \
for (iter = 0; \
iter < ARRAY_SIZE((c)->bucket_hash); \
iter++) \
hlist_for_each_entry_rcu((b), (c)->bucket_hash + iter, hash)
/* Recursing down the btree */
struct btree_op {
/* for waiting on btree reserve in btree_split() */
wait_queue_entry_t wait;
/* Btree level at which we start taking write locks */
short lock;
unsigned int insert_collision:1;
static inline void bch_btree_op_init(struct btree_op *op, int write_lock_level)
memset(op, 0, sizeof(struct btree_op));
op->lock = write_lock_level;
static inline void rw_lock(bool w, struct btree *b, int level)
w ? down_write_nested(&b->lock, level + 1)
: down_read_nested(&b->lock, level + 1);
if (w)
static inline void rw_unlock(bool w, struct btree *b)
if (w)
(w ? up_write : up_read)(&b->lock);
void bch_btree_node_read_done(struct btree *b);
void __bch_btree_node_write(struct btree *b, struct closure *parent);
void bch_btree_node_write(struct btree *b, struct closure *parent);
void bch_btree_set_root(struct btree *b);
struct btree *__bch_btree_node_alloc(struct cache_set *c, struct btree_op *op,
int level, bool wait,
struct btree *parent);
struct btree *bch_btree_node_get(struct cache_set *c, struct btree_op *op,
struct bkey *k, int level, bool write,
struct btree *parent);
int bch_btree_insert_check_key(struct btree *b, struct btree_op *op,
struct bkey *check_key);
int bch_btree_insert(struct cache_set *c, struct keylist *keys,
atomic_t *journal_ref, struct bkey *replace_key);
int bch_gc_thread_start(struct cache_set *c);
void bch_initial_gc_finish(struct cache_set *c);
void bch_moving_gc(struct cache_set *c);
int bch_btree_check(struct cache_set *c);
void bch_initial_mark_key(struct cache_set *c, int level, struct bkey *k);
static inline void wake_up_gc(struct cache_set *c)
static inline void force_wake_up_gc(struct cache_set *c)
* Garbage collection thread only works when sectors_to_gc < 0,
* calling wake_up_gc() won't start gc thread if sectors_to_gc is
* not a nagetive value.
* Therefore sectors_to_gc is set to -1 here, before waking up
* gc thread by calling wake_up_gc(). Then gc_should_run() will
* give a chance to permit gc thread to run. "Give a chance" means
* before going into gc_should_run(), there is still possibility
* that c->sectors_to_gc being set to other positive value. So
* this routine won't 100% make sure gc thread will be woken up
* to run.
atomic_set(&c->sectors_to_gc, -1);
#define MAP_DONE 0
#define MAP_CONTINUE 1
#define MAP_ALL_NODES 0
#define MAP_LEAF_NODES 1
#define MAP_END_KEY 1
typedef int (btree_map_nodes_fn)(struct btree_op *b_op, struct btree *b);
int __bch_btree_map_nodes(struct btree_op *op, struct cache_set *c,
struct bkey *from, btree_map_nodes_fn *fn, int flags);
static inline int bch_btree_map_nodes(struct btree_op *op, struct cache_set *c,
struct bkey *from, btree_map_nodes_fn *fn)
return __bch_btree_map_nodes(op, c, from, fn, MAP_ALL_NODES);
static inline int bch_btree_map_leaf_nodes(struct btree_op *op,
struct cache_set *c,
struct bkey *from,
btree_map_nodes_fn *fn)
return __bch_btree_map_nodes(op, c, from, fn, MAP_LEAF_NODES);
typedef int (btree_map_keys_fn)(struct btree_op *op, struct btree *b,
struct bkey *k);
int bch_btree_map_keys(struct btree_op *op, struct cache_set *c,
struct bkey *from, btree_map_keys_fn *fn, int flags);
typedef bool (keybuf_pred_fn)(struct keybuf *buf, struct bkey *k);
void bch_keybuf_init(struct keybuf *buf);
void bch_refill_keybuf(struct cache_set *c, struct keybuf *buf,
struct bkey *end, keybuf_pred_fn *pred);
bool bch_keybuf_check_overlapping(struct keybuf *buf, struct bkey *start,
struct bkey *end);
void bch_keybuf_del(struct keybuf *buf, struct keybuf_key *w);
struct keybuf_key *bch_keybuf_next(struct keybuf *buf);
struct keybuf_key *bch_keybuf_next_rescan(struct cache_set *c,
struct keybuf *buf,
struct bkey *end,
keybuf_pred_fn *pred);
void bch_update_bucket_in_use(struct cache_set *c, struct gc_stat *stats);